ICD-9-CM Volume 3

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The nervous system is a highly specialized network whose principal components are nerves called neurons. Neurons are interconnected to each other in complex arrangements, and have the property of conducting, using electrochemical signals, a great variety of stimuli both within the nervous tissue as well as from and towards most of the other tissues. Thus, neurons coordinate multiple functions in organisms. Nervous systems are found in many multicellular animals but differ greatly in complexity between species.

The human nervous system can be observed both with gross anatomy, (which describes the parts that are large enough to be seen with the plain eye,) and microanatomy, (which describes the system at a cellular level.) At gross anatomy, the nervous system can be grouped in distinct organs, these being actually stations which the neural pathways cross through. Thus, with a didactical purpose, these organs, according to their ubication, can be divided in two parts: the central nervous system (CNS) and the peripheral nervous system (PNS).

The central nervous system (CNS) represents the largest part of the nervous system, including the brain and the spinal cord. The CNS is contained within the dorsal cavity, with the brain within the cranial cavity, and the spinal cord in the spinal cavity. The CNS is covered by the meninges. The brain is also protected by the skull, and the spinal cord is also protected by the vertebrae. The nervous system can be connected into many systems that can function together. The two systems are central nervous system (CNS)and the peripheral nervous system (PNS).

The PNS consists of all the other nervous structures that do not lie within it. The large majority of what are commonly called nerves (which are actually axonal processes of nerve cells) are considered to be PNS.

The nervous system is, on a small scale, primarily made up of neurons. However, glial cells also play a major role.

Neurons

They are the core components of both the central nervous system & peripheral nervous system. Neurons are sensors that send electric messages to the Central Nervous System which send the electric messages back to the neurons telling them how to react, where the messages are finally sent back directly to the brain. These messages travel at a usual pace of 100 meters per second.

Glial cells are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the nervous system. In the human brain, glia are estimated to outnumber neurons by about 10 to 1.^[1]

Glial cells provide support and protection for neurons. They are thus known as the “glue” of the nervous system. The four main functions of glial cells are to surround neurons and hold them in place, to supply nutrients and oxygen to neurons, to insulate one neuron from another, and to destroy pathogens and remove dead neurons.

A less anatomical but much more functional division of the human nervous system is that classifying it according to the role that the different neural pathways play, regardless whether these cross through the CNS or the PNS:

The somatic nervous system is responsible for coordinating the body’s movements, and also for receiving external stimuli. It is the system that regulates activities that are under conscious control.

The autonomic nervous system is then split into the sympathetic division, parasympathetic division, and enteric division. The sympathetic nervous system responds to impending danger or stress, and is responsible for the increase of one’s heartbeat and blood pressure, among other physiological changes, along with the sense of excitement one feels due to the increase of adrenaline in the system. The parasympathetic nervous system, on the other hand, is evident when a person is resting and feels relaxed, and is responsible for such things as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels, and the stimulation of the digestive and genitourinary systems. The role of the enteric nervous system is to manage every aspect of digestion, from the esophagus to the stomach, small intestine and colon.

In turn, these pathways can be divided according to the direction in which they conduct stimuli:

• Afferent system by sensory neurons, which carry impulses from a receptor to the CNS
• Efferent system by motor neurons, which carry impulses from the CNS to an effector
• Relay system by relay neurons (also called interneurons), which transmit impulses between the sensory and motor neurones.

A useful mnemonic to remember the nature of Afferent vs Efferent is SAME DAVE: Sensory Afferent, Motor Efferent; Dorsal Afferent, Ventral Efferent

However, there are relay neurons in the CNS as well.

The junction between two neurones is called a synapse. There is a very narrow gap (about 20nm in width) between the neurons – the synaptic cleft, where an action potential is transmitted from one neuron to a neighboring one. They do this by relaying the message with the use of neurotransmitters which the next neuron then receives the electrical signal, known as a nerve impulse. The nerve impulse is determined by the neurotransmitter to then carry the message to its appropriate destination. These nerve impulses are a change in ion balance in the nerve cell, which the central nervous system can then interpret. The fact that the nervous system uses a mixture of electrical and chemical signals makes it incredibly fast, which is necessary to acknowledge the presence of danger. For example, a hand touching a hot stove. If the nervous system was only comprised of chemical signals, the body would not tell the arm to move fast enough to escape dangerous burns. So the speed of the nervous system is a necessity for life.

Some landmarks of embryonic neural development include the birth and differentiation of neurons from stem cell precursors, the migration of immature neurons from their birthplaces in the embryo to their final positions, outgrowth of axons from neurons and guidance of the motile growth cone through the embryo towards postsynaptic partners, the generation of synapses between these axons and their postsynaptic partners, and finally the lifelong changes in synapses which are thought to underlie learning and memory.

Many people have lost basic motor skills and other skills because of spinal chord injuries. If this portion is damaged, the biggest nerve and the most important one gets damaged. This leads to paralysis or other permanent damages.

The nervous system is able to make basic motor skills and other skills possible. The basic 5 senses of texture, taste, sight, smell,and hearing are powered by the nervous system. If disabled, basic motor skills may be lost.

The nervous system of all vertebrate animals, is often divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord.

Planaria, a type of flatworm, have dual nerve cords running along the length of the body and merging at the tail and the mouth. These nerve cords are connected by transverse nerves like the rungs of a ladder. These transverse nerves help coordinate the two sides of the animal. Two large ganglia at the head end function similar to a simple brain. Photoreceptors on the animal’s eyespots provide sensory information on light and dark.

The nervous system of the roundworm Caenorhabditis elegans has been mapped out to the cellular level. Every neuron and its cellular lineage has been recorded and most, if not all, of the neural connections are known. In this species, the nervous system is sexually dimorphic; the nervous systems of the two sexes, males and hermaphrodites, have different numbers of neurons and groups of neurons that perform sex-specific functions. In C. elegans, males have exactly 383 neurons, while hermaphrodites have exactly 302 neurons [2]

Arthropods, such as insects and crustaceans, have a nervous system made up of a series of ganglia, connected by a ventral nerve cord made up of two parallel connectives running along the length of the belly [3]. Typically, each body segment has one ganglion on each side, though some ganglia are fused to form the brain and other large ganglia [4].

The head segment contains the brain, also known as the supraesophageal ganglion. In the insect nervous system, the brain is anatomically divided into the protocerebrum, deutocerebrum, and tritocerebrum. Immediately behind the brain is the subesophageal ganglion, which is composed of three pairs of fused ganglia. It controls the mouthparts, the salivary glands and certain muscles.

Many arthropods have well-developed sensory organs, including compound eyes for vision and antennae for olfaction and pheromone sensation. The sensory information from these organs is processed by the brain.

Neural development in most species have many similarities neural development in humans.

• Neuroscience for Kids
• The Human Brain Project Homepage
• Kimball’s Biology Pages, CNS
• Kimball’s Biology Pages, PNS

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Editors-In-Chief: C. Michael Gibson, M.S., M.D. [1] and Stephanie Fernandez, M.D. [2]

The endocrine system is an integrated system of small organs that involve the release of extracellular signaling molecules known as hormones. The endocrine system is instrumental in regulating metabolism, growth and development and puberty, tissue function, and plays a part also in mood.^[1] The field of medicine that deals with disorders of endocrine glands is endocrinology, a branch of the wider field of internal medicine.

The Endocrine system is an information signal system much like the nervous system. However, the nervous system uses nerves to conduct information, whereas the endocrine system mainly uses blood vessels as information channels. Glands located in many regions of the body release into the bloodstream specific chemical messengers called hormones. Hormones regulate the many and varied functions of an organism, e.g., mood, growth and development, tissue function, and metabolism, as well as sending messages and acting on them.

The typical mode of cell signaling in the endocrine system is endocrine signaling. However, there are also other modes, i.e., paracrine, autocrine, and neuroendocrine signaling ^[2]. Purely neurocrine signaling between neurons, on the other hand, belongs completely to the nervous system.

A number of glands that signal each other in sequence is usually referred to as an axis, for example the Hypothalamic-pituitary-adrenal axis.

Typical endocrine glands are the pituitary, thyroid, and adrenal glands. Features of endocrine glands are, in general, their ductless nature, their vascularity, and usually the presence of intracellular vacuoles or granules storing their hormones. In contrast exocrine glands such as salivary glands, sweat glands, and glands within the gastrointestinal tract tend to be much less vascular and have ducts or a hollow lumen.

Other signaling can target the same cell.

Paracrine signaling is where the target cell is nearby.

Juxtacrine signals are transmitted along cell membranes via protein or lipid components integral to the membrane and are capable of affecting either the emitting cell or cells immediately adjacent.

Diseases of the endocrine system are common,^[3] including diseases such as diabetes mellitus, thyroid disease, and obesity. Endocrine disease is characterised by dysregulated hormone release (a productive Pituitary adenoma), inappropriate response to signalling (Hypothyroidism), lack or destruction of a gland (Diabetes mellitus type 1, diminished erythropoiesis in Chronic renal failure), or structural enlargement in a critical site such as the neck (Toxic multinodular goitre). Hypofunction of endocrine glands can occur as result of loss of reserve, hyposecretion, agenesis, atrophy, or active destruction. Hyperfunction can occur as result of hypersecretion, loss of suppression, hyperplastic, or neoplastic change, or hyperstimulation.

Endocrinopathies are classified as primary, secondary, or tertiary. Primary endocrine disease inhibits the action of downstream glands. Tertiary endocrine disease is associated with dysfunction of the hypothalamus and its releasing hormones.

Cancer can occur in endocrine glands, such as the thyroid, and hormones have been implicated in signalling distant tissues to proliferate, for example the Estrogen receptor has been shown to be involved in certain breast cancers. Endocrine, Paracrine, and autocrine signalling have all been implicated in proliferation, one of the required steps of oncogenesis.^[4]

This is a table of the glands of the endocrine system, and their secreted hormones

These originate either from the ovarian follicle or the corpus luteum.

• Releasing hormones
• Neuroendocrinology
• Nervous system
• Endocrine disruptor
• Major systems of the human body

• Journals Designed for Clinical Endocrinologists

• Islet cell antibody
• Binding of antibody to pancreas
• Kidshealth.org

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Eyes are organs that detect light. Different kinds of light-sensitive organs are found in a variety of animals. The simplest eyes do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms but hardly can be called vision. More complex eyes can distinguish shapes and colors. The visual fields of some such complex eyes largely overlap, to allow better depth perception (binocular vision), as in humans; and others are placed so as to minimize the overlap, such as in rabbits and chameleons.

In the human eye, light enters the pupil and is focused on the retina by the lens. Light-sensitive nerve cells called rods (for brightness) and cones (for color) react to the light. They interact with each other and send messages to the brain that indicate brightness, color, and contour.

The first proto-eyes evolved among animals 540 million years ago. Almost all animals have eyes, or descend from animals that did.

In most vertebrates and some mollusks, the eye works by allowing light to enter it and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris which regulates the intensity of the light that enters the eye. The eyes of cephalopods, fish, amphibians and snakes usually have fixed lens shapes, and focusing vision is achieved by telescoping the lens—similar to how a camera focuses.

Compound eyes are found among the arthropods and are composed of many simple facets which give a pixelated image (not multiple images, as is often believed). Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360-degree field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating multiple-image vision. With each eye viewing a different angle, a fused image from all the eyes is produced in the brain, providing very wide-angle, high-resolution images.

Possessing detailed hyperspectral color vision, the Mantis shrimp has been reported to have the world’s most complex color vision system.^[1] Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of lenses in one eye.

Some of the simplest eyes, called ocelli, can be found in animals like snails, who cannot actually “see” in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out of direct sunlight. Jumping spiders have simple eyes that are so large, supported by an array of other, smaller eyes, that they can get enough visual input to hunt and pounce on their prey. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which gives a rough image.

Biologists use the theory of evolution to explain the origin and development of eyes, as well as of organs in general.

The common origin (monophyly) of all animal eyes is established by shared anatomical and genetic features of all eyes; that is, all modern eyes, varied as they are, have their origins in a proto-eye evolved some 540 million years ago.^[2][3][4] The majority of the advancements in early eyes are believed to have taken only a few million years to develop, as the first predator to gain true imaging would have touched off an “arms race”,^[5] or rather, a phylogenetic radiation from the species with that first proto-eye, among the descendents of which, there may well have been an “arms race”. Prey animals and competing predators alike would be forced to rapidly match or exceed any such capabilities to survive. Hence multiple eye types and subtypes developed in parallel.

Vision in various animals shows adaptation to environmental requirements. For example, birds of prey have much greater visual acuity than humans, and some can see ultraviolet light. The different forms of eyes in, for example, vertebrates and mollusks are often cited as examples of parallel evolution, despite their distant common ancestry.

The earliest eyes, called “eyespots”, were simple patches of photoreceptor cells, or light-sensitive proteins in unicellular organisms, physically similar to the receptor patches for taste and smell. These eyespots could only sense ambient brightness: they could distinguish light and dark, but not the direction of the lightsource.^[6] This gradually changed as the eyespot depressed into a shallow “cup” shape, granting the ability to slightly discriminate directional brightness by using the angle at which the light hit certain cells to identify the source. The pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of slightly distinguishing dim shapes.^[7]

The thin overgrowth of transparent cells over the eye’s aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialize into a transparent humour that optimized color filtering, blocked harmful radiation, improved the eye’s refractive index, and allowed functionality outside of water. The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with the transparent crystallin protein.^[8]

The structure of the mammalian eye can be divided into three main layers or tunics whose names reflect their basic functions: the fibrous tunic, the vascular tunic, and the nervous tunic.^[9][10][11]

• The fibrous tunic, also known as the tunica fibrosa oculi, is the outer layer of the eyeball consisting of the cornea and sclera.^[12] The sclera gives the eye most of its white color. It consists of dense connective tissue filled with the protein collagen to both protect the inner components of the eye and maintain its shape.^[13]

• The vascular tunic, also known as the tunica vasculosa oculi, is the middle vascularized layer which includes the iris, ciliary body, and choroid.^[12][14][15] The choroid contains blood vessels that supply the retinal cells with necessary oxygen and remove the waste products of respiration. The choroid gives the inner eye a dark color, which prevents disruptive reflections within the eye.

• The nervous tunic, also known as the tunica nervosa oculi, is the inner sensory which includes the retina.^[12][15] The retina contains the photosensitive rod and cone cells and associated neurons. To maximise vision and light absorption, the retina is a relatively smooth (but curved) layer. It has two points at which it is different; the fovea and optic disc. The fovea is a dip in the retina directly opposite the lens, which is densely packed with cone cells. It is largely responsible for color vision in humans, and enables high acuity, such as is necessary in reading. The optic disc, sometimes referred to as the anatomical blind spot, is a point on the retina where the optic nerve pierces the retina to connect to the nerve cells on its inside. No photosensitive cells exist at this point, it is thus “blind”. In addition to the rods and cones, a small proportion (about 2% in humans) of the ganglion cells in the retina are photosensitive through the pigment melanopsin. They are generally most excitable by blue light, about 470 nm. Their information is sent to the SCN (suprachiasmatic nuclei), not to the visual center, through the retinohypothalamic tract, not via the optic nerve. It is these light signals which regulate circadian rhythms in mammals and several other animals. Many, but not all, totally blind individuals have their circadian rhythms adjusted daily in this way.

The mammalian eye can also be divided into two main segments: the anterior segment and the posterior segment.^[16]

The posterior segment is the back two-thirds of the eye that includes the anterior hyaloid membrane and all structures behind it: the vitreous humor, retina, choroid, and optic nerve.^[17] On the other side of the lens is the second humour, the vitreous humour, which is bounded on all sides: by the lens, ciliary body, suspensory ligaments and by the retina. It lets light through without refraction, helps maintain the shape of the eye and suspends the delicate lens. In some animals, the retina contains a reflective layer (the tapetum lucidum) which increases the amount of light each photosensitive cell perceives, allowing the animal to see better under low light conditions.

In many species, the eyes are inset in the portion of the skull known as the orbits or eyesockets. This placement of the eyes helps to protect them from injury.

In humans, the eyebrows redirect flowing substances (such as rainwater or sweat) away from the eye. Water in the eye can alter the refractive properties of the eye and blur vision. It can also wash away the tear fluid—along with it the protective lipid layer—and can alter corneal physiology, due to osmotic differences between tear fluid and freshwater. Osmotic effects are made apparent when swimming in freshwater pools, as the osmotic gradient draws “pool water” into the corneal tissue (the pool water is hypotonic), causing edema, and subsequently leaving the swimmer with “cloudy” or “misty” vision for a short period thereafter. The edema can be reversed by irrigating the eye with hypertonic saline which osmotically draws the excess water out of the eye.

In many animals, including humans, eyelids wipe the eye and prevent dehydration. They spread tears on the eyes, which contains substances which help fight bacterial infection as part of the immune system. Some aquatic animals have a second eyelid in each eye which refracts the light and helps them see clearly both above and below water. Most creatures will automatically react to a threat to its eyes (such as an object moving straight at the eye, or a bright light) by covering the eyes, and/or by turning the eyes away from the threat. Blinking the eyes is, of course, also a reflex.

In many animals, including humans, eyelashes prevent fine particles from entering the eye. Fine particles can be bacteria, but also simple dust which can cause irritation of the eye, and lead to tears and subsequent blurred vision.

The structure of the mammalian eye owes itself completely to the task of focusing light onto the retina. This light causes chemical changes in the photosensitive cells of the retina, the products of which trigger nerve impulses which travel to the brain.

The retina contains two forms of photosensitive cells important to vision—rods and cones. Though structurally and metabolically similar, their function is quite different. Rod cells are highly sensitive to light, allowing them to respond in dim light and dark conditions; however, they cannot detect color differences. These are the cells that allow humans and other animals to see by moonlight, or with very little available light (as in a dark room). Cone cells, conversely, need high light intensities to respond and have high visual acuity. Different cone cells respond to different wavelengths of light, which allows an organism to see color. The shift from cone vision to rod vision is why the darker conditions become, the less color objects seem to have.

The differences between rods and cones are useful; apart from enabling sight in both dim and light conditions, they have further advantages. The fovea, directly behind the lens, consists of mostly densely-packed cone cells. The fovea gives humans a highly detailed central vision, allowing reading, bird watching, or any other task which primarily requires staring at things. Its requirement for high intensity light does cause problems for astronomers, as they cannot see dim stars, or other celestial objects, using central vision because the light from these is not enough to stimulate cone cells. Because cone cells are all that exist directly in the fovea, astronomers have to look at stars through the “corner of their eyes” (averted vision) where rods also exist, and where the light is sufficient to stimulate cells, allowing an individual to observe faint objects.

Rods and cones are both photosensitive, but respond differently to different frequencies of light. They contain different pigmented photoreceptor proteins. Rod cells contain the protein rhodopsin and cone cells contain different proteins for each color-range. The process through which these proteins go is quite similar — upon being subjected to electromagnetic radiation of a particular wavelength and intensity, the protein breaks down into two constituent products. Rhodopsin, of rods, breaks down into opsin and retinal; iodopsin of cones breaks down into photopsin and retinal. The opsin in each opens ion channels on the cell membrane, which leads to hyperpolarization; this hyperpolarization of the cell leads to a release of transmitter molecules at the synapse.

Differences between the rhodopsin and the iodopsins is the reason why cones and rods enable organisms to see in dark and light conditions — each of the photoreceptor proteins requires a different light intensity to break down into the constituent products. Further, synaptic convergence means that several rod cells are connected to a single bipolar cell, which then connects to a single ganglion cell by which information is relayed to the visual cortex. This convergence is in direct contrast to the situation with cones, where each cone cell is connected to a single bipolar cell. This divergence results in the high visual acuity, or the high ability to distinguish detail, of cone cells compared to rods. If a ray of light were to reach just one rod cell, the cell’s reponse may not be enough to hyperpolarize the connected bipolar cell. But because several “converge” onto a bipolar cell, enough transmitter molecules reach the synapses of the bipolar cell to hyperpolarize it.

Furthermore, color is distinguishable due to the different iodopsins of cone cells; there are three different kinds, in normal human vision, which is why we need three different primary colors to make a color space.

Visual acuity is often measured in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measured by bar charts of different numbers of white–black stripe cycles. For example, if each pattern is 1.75 cm wide and is placed at 1 m distance from the eye, it will subtend an angle of 1 degree, so the number of white–black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a gray block, is then the measurement of visual acuity of the eye.

For a human eye with excellent acuity, the maximum theoretical resolution would be 50 CPD^[18] (1.2 minute of arc per line pair, or a 0.35 mm line pair, at 1 m). However, the eye can only resolve a contrast of 5%. Taking this into account, the eye can resolve a maximum resolution of 37 CPD, or 1.6 minute of arc per line pair (0.47 mm line pair, at 1 m). ^[19] A rat can resolve only about 1 to 2 CPD.^[20] A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eye’s central fovea region.

A maximum resolution of the human eye in good light of 1.6 minute of arc per line pair will correspond to 1.25 lines per minute of arc. Assuming two pixels per line pair (one pixel per line) and a square field of 120 degrees, this would be equivalent to approximately 120×60×1.25 = 9000 pixels in each of the X and Y dimensions, or about 81 megapixels.

However, the human eye itself has only a small spot of sharp vision in the middle of the retina, the fovea centralis, the rest of the field of view being progressively lower resolution as it gets further from the fovea. The angle of the sharp vision being just a few degrees in the middle of the view, the sharp area thus barely achieves even a single megapixel resolution. The experience of wide sharp human vision is in fact based on turning the eyes towards the current point of interest in the field of view, the brain thus perceiving an observation of a wide sharp field of view.

The narrow beam of sharp vision is easy to test by putting a fingertip on a newspaper and trying to read the text while staring at the fingertip — it is very difficult to read text that’s just a few centimeters away from the fingertip.

Human eyes respond to light with wavelength in the range of approximately 400 to 700 nm. Other animals have other ranges, with many such as birds including a significant ultraviolet (shorter than 400 nm) response.

The retina has a static contrast ratio of around 100:1 (about 6 1/2 stops). As soon as the eye moves (saccades) it re-adjusts its exposure both chemically and by adjusting the iris. Initial dark adaptation takes place in approximately four seconds of profound, uninterrupted darkness; full adaptation through adjustments in retinal chemistry (the Purkinje effect) are mostly complete in thirty minutes. Hence, a dynamic contrast ratio of about 1,000,000:1 (about 20 stops) is possible. The process is nonlinear and multifaceted, so an interruption by light nearly starts the adaptation process over again. Full adaptation is dependent on good blood flow; thus dark adaptation may be hampered by poor circulation, and vasoconstrictors like alcohol or tobacco.

The visual system in the brain is too slow to process that information if the images are slipping across the retina at more than a few degrees per second.^[21] Thus, for humans to be able to see while moving, the brain must compensate for the motion of the head by turning the eyes. Another complication for vision in frontal-eyed animals is the development of a small area of the retina with a very high visual acuity. This area is called the fovea, and covers about 2 degrees of visual angle in people. To get a clear view of the world, the brain must turn the eyes so that the image of the object of regard falls on the fovea. Eye movements are thus very important for visual perception, and any failure to make them correctly can lead to serious visual disabilities.

Having two eyes is an added complication, because the brain must point both of them accurately enough that the object of regard falls on corresponding points of the two retinas; otherwise, double vision would occur. The movements of different body parts are controlled by striated muscles acting around joints. The movements of the eye are no exception, but they have special advantages not shared by skeletal muscles and joints, and so are considerably different.

Each eye has six muscles that control its movements: the lateral rectus, the medial rectus, the inferior rectus, the superior rectus, the inferior oblique, and the superior oblique. When the muscles exert different tensions, a torque is exerted on the globe that causes it to turn, in almost pure rotation, with only about one millimeter of translation.^[22] Thus, the eye can be considered as undergoing rotations about a single point in the center of the eye. Once the human eye sustains damage to the optic nerve, the impulses will not be taken to the brain. Eye transplants can happen but the person receiving the transplant will not be able to see. As for the optic nerve, once it is damaged it cannot be fixed.

Rapid eye movement, or REM for short, typically refers to the stage during sleep during which the most vivid dreams occur. During this stage, the eyes move rapidly. It is not in itself a unique form of eye movement.

Saccades are quick, simultaneous movements of both eyes in the same direction controlled by the frontal lobe of the brain.

Even when looking intently at a single spot, the eyes drift around. This ensures that individual photosensitive cells are continually stimulated in different degrees. Without changing input, these cells would otherwise stop generating output. Microsaccades move the eye no more than a total of 0.2° in adult humans.

The vestibulo-ocular reflex is a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual field. For example, when the head moves to the right, the eyes move to the left, and vice versa.

The eyes can also follow a moving object around. This tracking is less accurate than the vestibulo-ocular reflex, as it requires the brain to process incoming visual information and supply feedback. Following an object moving at constant speed is relatively easy, though the eyes will often make saccadic jerks to keep up. The smooth pursuit movement can move the eye at up to 100°/s in adult humans.

It is more difficult to visually estimate speed in low light conditions or while moving, unless there is another point of reference for determining speed.

The optokinetic reflex is a combination of a saccade and smooth pursuit movement. When, for example, looking out of the window in a moving train, the eyes can focus on a ‘moving’ tree for a short moment (through smooth pursuit), until the tree moves out of the field of vision. At this point, the optokinetic reflex kicks in, and moves the eye back to the point where it first saw the tree (through a saccade).

File:Stereogram Tut Eye Convergence.png

When a creature with binocular vision looks at an object, the eyes must rotate around a vertical axis so that the projection of the image is in the centre of the retina in both eyes. To look at an object closer by, the eyes rotate ‘towards each other’ (convergence), while for an object farther away they rotate ‘away from each other’ (divergence). Exaggerated convergence is called cross eyed viewing (focusing on the nose for example) . When looking into the distance, or when ‘staring into nothingness’, the eyes neither converge nor diverge.

Vergence movements are closely connected to accommodation of the eye. Under normal conditions, changing the focus of the eyes to look at an object at a different distance will automatically cause vergence and accommodation.

To see clearly, the lens will be pulled flatter or allowed to regain its thicker form.

There are many diseases, disorders, and age-related changes that may affect the eyes and surrounding structures.

As the eye ages certain changes occur that can be attributed solely to the aging process. Most of these anatomic and physiologic processes follow a gradual decline. With aging, the quality of vision worsens due to reasons independent of aging eye diseases. While there are many changes of significance in the nondiseased eye, the most functionally important changes seem to be a reduction in pupil size and the loss of accommodation or focusing capability (presbyopia). The area of the pupil governs the amount of light that can reach the retina. The extent to which the pupil dilates also decreases with age. Because of the smaller pupil size, older eyes receive much less light at the retina. In comparison to younger people, it is as though older persons wear medium-density sunglasses in bright light and extremely dark glasses in dim light. Therefore, for any detailed visually guided tasks on which performance varies with illumination, older persons require extra lighting. Certain ocular diseases can come from sexually transmitted diseases such as herpes and genital warts. If contact between eye and area of infection occurs, the STD will be transmitted to the eye.^[23]

With aging a prominent white ring develops in the periphery of the cornea- called arcus senilis. Aging causes laxity and downward shift of eyelid tissues and atrophy of the orbital fat. These changes contribute to the etiology of several eyelid disorders such as ectropion, entropion, dermatochalasis, and ptosis. The vitreous gel undergoes liquefaction (posterior vitreous detachment or PVD) and its opacities—visible as floaters—gradually increase in number.

Various eye care professionals, including ophthalmologists, optometrists, and opticians, are involved in the treatment and management of ocular and vision disorders. A Snellen chart is one type of eye chart used to measure visual acuity. At the conclusion of an eye examination, an eye doctor may provide the patient with an eyeglass prescription for corrective lenses

Accidents involving common household products cause 125,000 eye injuries each year in the U.S.^[24] More than 40,000 people a year suffer eye injuries while playing sports.^[24] Sports-related eye injuries occur most frequently in baseball, basketball and racquet sports.^[24]

Each day about 2000 U.S. workers have a job-related eye injury that requires medical treatment.^[25] About one third of the injuries are treated in hospital emergency departments and more than 100 of these injuries result in one or more days of lost work.^[25] The majority of these injuries result from small particles or objects striking or abrading the eye. Examples include metal slivers, wood chips, dust, and cement chips that are ejected by tools, wind blown, or fall from above a worker. Some of these objects, such as nails, staples, or slivers of wood or metal penetrate the eyeball and result in a permanent loss of vision. Large objects may also strike the eye/face causing blunt force trauma to the eyeball or eye socket. Chemical burns to one or both eyes from splashes of industrial chemicals or cleaning products are common. Thermal burns to the eye occur as well. Among welders, their assistants, and nearby workers, UV radiation burns (welder’s flash) routinely damage workers’ eyes and surrounding tissue. In addition to common eye injuries, health care workers, laboratory staff, janitorial workers, animal handlers, and other workers may be at risk of acquiring infectious diseases via ocular exposure.^[25]

• Ophthalmology
• Eye exam
• Infant vision
• Annulus of Zinn
• Conjunctiva
• Macula
• Nictitating membrane
• Schlemm’s canal
• Trabecular meshwork

• “Anatomy”. History of Ophthalmology. Unknown parameter |accessdaymonth= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
• Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science, 4th ed. McGraw-Hill, New York (2000). ISBN 0-8385-7701-6

• DJO | Digital Journal of Ophthalmology
• Glossary of Eye Conditions
• Evolution of the Eye
• Diagram of the eye
• Webvision. The organisation of the retina and visual system.
• VisionSimulations.com | Images and vision simulators of various diseases and conditions of the eye
• Eyes and computers.
• Eyeatlas online (ophthalmological images) by Umberto Benelli, MD, PhD
• ClarkVision’s estimation of the resolution of the eye
• Video: Vision and How Our Eyes Work
• Summary of eye diseases and disorders
• Your Baby’s Eyes.
• National Institute for Occupational Safety and Health – Eye Safety

Template:Eye Template:Visual system Template:Human anatomical features Template:Muscles of orbit

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The ear is the sense organ that detects sounds. The vertebrate ear shows a common biology from fish to humans, with variations in structure according to order and species. It not only acts as a receiver for sound, but plays a major role in the sense of balance and body position. The ear is part of the auditory system.

The word “ear” may be used correctly to describe the entire organ or just the visible portion. In most animals, the visible ear is a flap of tissue that is also called the pinna. The pinna may be all that shows of the ear, but it serves only the first of many steps in hearing and plays no role in the sense of balance. In people, the pinna is often called the auricle. Vertebrates have a pair of ears, placed symmetrically on opposite sides of the head. This arrangement aids in the ability to localize sound sources.

Audition is the scientific name for the perception of sound. Sound is a form of energy that moves through air, water, and other matter, in waves of pressure. Sound is the means of auditory communication, including frog calls, bird songs and spoken language. Although the ear is the vertebrate sense organ that recognizes sound, it is the brain and central nervous system that “hears”. Sound waves are perceived by the brain through the firing of nerve cells in the auditory portion of the central nervous system. The ear changes sound pressure waves from the outside world into a signal of nerve impulses sent to the brain.

The outer part of the ear collects sound. That sound pressure is amplified through the middle portion of the ear and, in land animals, passed from the medium of air into a liquid medium. The change from air to liquid occurs because air surrounds the head and is contained in the ear canal and middle ear, but not in the inner ear. The inner ear is hollow, embedded in the temporal bone, the densest bone of the body. The hollow channels of the inner ear are filled with liquid, and contain a sensory epithelium that is studded with hair cells. The microscopic “hairs” of these cells are structural protein filaments that project out into the fluid. The hair cells are mechanoreceptors that release a chemical neurotransmitter when stimulated. Sound waves moving through fluid push the filaments; if the filaments bend over enough it causes the hair cells to fire. In this way sound waves are transformed into nerve impulses. In vision, the rods and cones of the retina play a similar role with light as the hair cells do with sound. The nerve impulses travel from the left and right ears through the eighth cranial nerve to both sides of the brain stem and up to the portion of the cerebral cortex dedicated to sound. This auditory part of the cerebral cortex is in the temporal lobe.

The part of the ear that is dedicated to sensing balance and position also sends impulses through the eighth cranial nerve, the VIIIth nerve’s Vestibular Portion. Those impulses are sent to the vestibular portion of the central nervous system. The human ear can generally hear sounds with frequencies between 20 Hz and 20 kHz (the audio range). Although the sensation of hearing requires an intact and functioning auditory portion of the central nervous system as well as a working ear, human deafness (extreme insensitivity to sound) most commonly occurs because of abnormalities of the inner ear, rather than the nerves or tracts of the central auditory system.^[1]

The shape of outer ear of mammals varies widely across species. However the inner workings of mammalian ears (including humans’) are very similar.

The outer ear is the most external portion of the ear. The outer ear includes the pinna (also called auricle), the ear canal, and the very most superficial layer of the ear drum (also called the tympanic membrane). In humans, and almost all vertebrates, the only visible portion of the ear is the outer ear. Although the word “ear” may properly refer to the pinna (the flesh covered cartilage appendage on either side of the head), this portion of the ear is not vital for hearing. The complicated design of the human outer ear does help capture sound (and imposes filtering that helps distinguish the direction of the sound source), but the most important functional aspect of the human outer ear is the ear canal itself. Unless the canal is open, hearing will be dampened. Ear wax (medical name – cerumen) is produced by glands in the skin of the outer portion of the ear canal. This outer ear canal skin is applied to cartilage; the thinner skin of the deep canal lies on the bone of the skull. Only the thicker cerumen-producing ear canal skin has hairs. The outer ear ends at the most superficial layer of the tympanic membrane. The tympanic membrane is commonly called the ear drum.

The pinna helps direct sound through the ear canal to the tympanic membrane (eardrum). The framework of the auricle consists of a single piece of yellow fibrocartilage with a complicated relief on the anterior, concave side and a fairly smooth configuration on the posterior, convex side. The Darwinian tubercle, which is present in some people, lies in the descending part of the helix and corresponds to the true ear tip of the long-eared mammals. The lobule merely contains subcutaneous tissue.^[2] In some animals with mobile pinnae (like the horse), each pinna can be aimed independently to better receive the sound. For these animals, the pinnae help localize the direction of the sound source. Human beings localize sound within the central nervous system, by comparing arrival-time differences and loudness from each ear, in brain circuits that are connected to both ears.

The auricles also have an effect on facial appearance. In Western societies, protruding ears (present in about 5% of ethnic Europeans) have been considered unattractive, particularly if asymmetric. The first surgery to reduce the projection of prominent ears was published in the medical literature in 1881.

The ears have also been ornamented with jewellery for thousands of years, traditionally by piercing of the earlobe. In some cultures, ornaments are placed to stretch and enlarge the earlobes to make them very large. Tearing of the earlobe from the weight of heavy earrings, or from traumatic pull of an earring (for example by snagging on a sweater being removed), is fairly common.^[3] The repair of such a tear is usually not difficult.

A cosmetic surgical procedure to reduce the size or change the shape of the ear is called an otoplasty. In the rare cases when no pinna is formed (atresia), or is extremely small (microtia) reconstruction the auricle is possible. Most often, a cartilage graft from another part of the body (generally, rib cartilage) is used to form the matrix of the ear, and skin grafts or rotation flaps are used to provide the covering skin. However, when babies are born without an auricle on one or both sides, or when the auricle is very tiny, the ear canal is ordinarily either small or absent, and the middle ear often has deformities. The initial medical intervention is aimed at assessing the baby’s hearing and the condition of the ear canal, as well as the middle and inner ear. Depending on the results of tests, reconstruction of the outer ear is done in stages, with planning for any possible repairs of the rest of the ear.^[4][5][6]

The middle ear, an air-filled cavity behind the ear drum (tympanic membrane), includes the three ear bones or ossicles: the malleus (or hammer), incus (or anvil), and stapes (or stirrup). The opening of the Eustachian tube is also within the middle ear. The malleus has a long process (the manubrium, or handle) that is attached to the mobile portion of the eardrum. The incus is the bridge between the malleus and stapes. The stapes is the smallest named bone in the human body. The three bones are arranged so that movement of the tympanic membrane causes movement of the malleus, which causes movement of the incus, which causes movement of the stapes. When the stapes footplate pushes on the oval window, it causes movement of fluid within the cochlea (a portion of the inner ear).

In humans and other land animals the middle ear (like the ear canal) is normally filled with air. Unlike the open ear canal, however, the air of the middle ear is not in direct contact with the atmosphere outside the body. The Eustachian tube connects from the chamber of the middle ear to the back of the pharynx. The middle ear is very much like a specialized paranasal sinus, called the tympanic cavity; it, like the paranasal sinuses, is a hollow mucosa-lined cavity in the skull that is ventilated through the nose. The mastoid portion of the human temporal bone, which can be felt as a bump in the skull behind the pinna, also contains air, which is ventilated through the middle ear. Template:Middle ear map Normally, the Eustachian tube is collapsed, but it gapes open both with swallowing and with positive pressure. When taking off in an airplane, the surrounding air pressure goes from higher (on the ground) to lower (in the sky). The air in the middle ear expands as the plane gains altitude, and pushes its way into the back of the nose and mouth. On the way down, the volume of air in the middle ear shrinks, and a slight vacuum is produced. Active opening of the Eustachian tube is required to equalize the pressure between the middle ear and the surrounding atmosphere as the plane descends. The diver also experiences this change in pressure, but with greater rates of pressure change; active opening of the Eustachian tube is required more frequently as the diver goes deeper into higher pressure.

The arrangement of the tympanic membrane and ossicles works to efficiently couple the sound from the opening of the ear canal to the cochlea. There are several simple mechanisms that combine to increase the sound pressure. The first is the “hydraulic principle”. The surface area of the tympanic membrane is many times that of the stapes footplate. Sound energy strikes the tympanic membrane and is concentrated to the smaller footplate. A second mechanism is the “lever principle”. The dimensions of the articulating ear ossicles lead to an increase in the force applied to the stapes footplate compared with that applied to the malleus. A third mechanism channels the sound pressure to one end of the cochlea, and protects the other end from being struck by sound waves. In humans, this is called “round window protection”, and will be more fully discussed in the next section.

Abnormalities such as impacted ear wax (occlusion of the external ear canal), fixed or missing ossicles, or holes in the tympanic membrane generally produce conductive hearing loss. Conductive hearing loss may also result from middle ear inflammation causing fluid build-up in the normally air-filled space. Tympanoplasty is the general name of the operation to repair the middle ear’s tympanic membrane and ossicles. Grafts from muscle fascia are ordinarily used to rebuild an intact ear drum. Sometimes artificial ear bones are placed to substitute for damaged ones, or a disrupted ossicular chain is rebuilt in order to conduct sound effectively.

Template:Inner ear map The inner ear includes both the organ of hearing (the cochlea) and a sense organ that is attuned to the effects of both gravity and motion (labyrinth or vestibular apparatus). The balance portion of the inner ear consists of three semi-circular canals and the vestibule. The inner ear is encased in the hardest bone of the body. Within this ivory hard bone, there are fluid-filled hollows. Within the cochlea are three fluid filled spaces: the tympanic canal, the vestibular canal, and the middle canal. The eighth cranial nerve comes from the brain stem to enter the inner ear. When sound strikes the ear drum, the movement is transferred to the footplate of the stapes, which presses into one of the fluid-filled ducts of the cochlea. The fluid inside this duct is moved, flowing against the receptor cells of the Organ of Corti, which fire. These stimulate the spiral ganglion, which sends information through the auditory portion of the eighth cranial nerve to the brain.

Hair cells are also the receptor cells involved in balance, although the hair cells of the auditory and vestibular systems of the ear are not identical. Vestibular hair cells are stimulated by movement of fluid in the semicircular canals and the utricle and saccule. Firing of vestibular hair cells stimulates the Vestibular portion of the eighth cranial nerve.^[7]

The auricle can be easily damaged. Because it is skin-covered cartilage, with only a thin padding of connective tissue, rough handling of the ear can cause enough swelling to jeopardize the blood-supply to its framework, the auricular cartilage. That entire cartilage framework is fed by a thin covering membrane called the perichondrium (meaning literally: around the cartilage). Any fluid from swelling or blood from injury that collects between the perichondrium and the underlying cartilage puts the cartilage in danger of being separated from its supply of nutrients. If portions of the cartilage starve and die, the ear never heals back into its normal shape. Instead, the cartilage becomes lumpy and distorted. Wrestler’s Ear is one term used to describe the result, because wrestling is one of the most common ways such an injury occurs. Cauliflower ear is another name for the same condition, because the thickened auricle can resemble that vegetable.

The lobule of the ear (ear lobe) is the one part of the human auricle that normally contains no cartilage. Instead, it is a wedge of adipose tissue (fat) covered by skin. There are many normal variations to the shape of the ear lobe, which may be small or large. Tears of the earlobe can be generally repaired with good results. Since there is no cartilage, there is not the risk of deformity from a blood clot or pressure injury to the ear lobe.

Other injuries to the external ear occur fairly frequently, and can leave a major deformity. Some of the more common ones include, laceration from glass, knives, and bite injuries, avulsion injuries, cancer, frostbite, and burns.

Ear canal injuries can come from firecrackers and other explosives, and mechanical trauma from placement of foreign bodies into the ear. The ear canal is most often self-traumatized from efforts at ear cleaning. The outer part of the ear canal rests on the flesh of the head; the inner part rests in the opening of the bony skull (called the external auditory meatus). The skin is very different on each part. The outer skin is thick, and contains glands as well as hair follicles. The glands make cerumen (also called ear wax). The skin of the outer part moves a bit if the pinna is pulled; it is only loosely applied to the underlying tissues. The skin of the bony canal, on the other hand, is not only among the most delicate skin in the human body, it is tightly applied to the underlying bone. A slender object used to blindly clean cerumen out of the ear often results instead with the wax being pushed in, and contact with the thin skin of the bony canal is likely to lead to laceration and bleeding.

Like outer ear trauma, middle ear trauma most often comes from blast injuries and insertion of foreign objects into the ear. Skull fractures that go through the part of the skull containing the ear structures (the temporal bone) can also cause damage to the middle ear. Small perforations of the tympanic membrane usually heal on their own, but large perforations may require grafting. Displacement of the ossicles will cause a conductive hearing loss that can only be corrected with surgery. Forcible displacement of the stapes into the inner ear can cause a sensory neural hearing loss that cannot be corrected even if the ossicles are put back into proper position. Because human skin has a top waterproof layer of dead skin cells that are constantly shedding, displacement of portions of the tympanic membrane or ear canal into the middle ear or deeper areas by trauma can be particularly traumatic. If the displaced skin lives within a closed area, the shed surface builds up over months and years and forms a cholesteatoma. The -oma ending of that word indicates a tumour in medical terminology, and although cholesteatoma is not a neoplasm (but a skin cyst), it can expand and erode the ear structures. The treatment for cholesteatoma is surgical.

There are two principal damage mechanisms to the inner ear in industrialized society, and both injure hair cells. The first is exposure to elevated sound levels (noise trauma), and the second is exposure to drugs and other substances (ototoxicity).

In 1972 the U.S. EPA told Congress that at least 34 million people were exposed to sound levels on a daily basis that are likely to lead to significant hearing loss.^[13] The worldwide implication for industrialized countries would place this exposed population in the hundreds of millions.

It has long been known that humans, and indeed other primates such as the orangutan and chimpanzee have ear muscles that are minimally developed and non-functional, yet still large enough to be easily identifiable.^[14] These undeveloped muscles are known as vestigial structures. A muscle that cannot move the ear, for whatever reason, can no longer be said to have any biological function. This serves as evidence of homology between related species. In humans there is variability in these muscles, such that some people are able to move their ears in various directions, and it has been said that it may be possible for others to gain such movement by repeated trials.^[14]

Only vertebrate animals have ears, although many invertebrates are able to detect sound using other kinds of sense organs. In insects, tympanal organs are used to hear distant sounds. They are not confined to the head, but can occur in different locations depending on the group of insects.^[15]

Simpler structures allow arthropods to detect near-at-hand sounds. Spiders and cockroaches, for example, have hairs on their legs which are used for detecting sound. Caterpillars may also have hairs on their body that perceive vibrations^[16] and allow them to respond to the sound.

Wikimedia Commons has media related to Ear.

• Protein behind hearing
• 3D Ear page
• Details of various ear problems
• Ear wiggling mechanism unmasked
• Cotton swabs can pose serious health risk: coroner from ctv.ca

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af:Oor ar:أذن ay:Jinchu az:Qulaq bar:Ohrwaschl bg:Ухо bn:কর্ণ (অঙ্গ) br:Skouarn bs:Uho ca:Orella cdo:Ngê cs:Ucho cy:Clust da:Øre de:Ohr diq:Goş el:Αυτί eo:Orelo et:Kõrv fi:Korva fiu-vro:Kõrv gd:Cluas gl:Orella he:אוזן hi:कान hr:Uho hu:Fül id:Telinga ig:Nti io:Orelo is:Eyra it:Orecchio jbo:kerlo ko:귀 la:Auris lt:Ausis ml:ചെവി mr:कान ms:Telinga nah:Nacaztli nl:Oor nn:Øyre no:Øre nrm:Ouothelle oc:Aurelha ps:غوږ qu:Rinri scn:Aricchiu simple:Ear sk:Ucho sl:Uho sq:Veshi sr:Уво su:Ceuli sv:Öra te:చెవి tg:Гӯш th:หู tl:Tainga uk:Вухо yi:אויער yo:Etí zh-min-nan:Hīⁿ

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Anatomically, a nose is a protuberance in vertebrates that houses the nostrils, or nares, which admit and expel air for respiration in conjunction with the mouth.

In most humans, it also houses the nosehairs, which catch airborne particles and prevent them from reaching the lungs. Within and behind the nose is the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passes through the pharynx, shared with the digestive system, and then into the rest of the respiratory system. In humans, the nose is located centrally on the face;on most other mammals, it is on the upper tip of the snout.

As an interface between the body and the external world, the nose and associated structures frequently perform additional functions concerned with conditioning entering air (for instance, by warming and/or humidifying it, also for flicking if moving and by mostly reclaiming moisture from the air before it is exhaled (as occurs most efficiently in camels).

In most mammals, the nose is the primary organ for smelling. As the animal sniffs, the air flows through the nose and over structures called turbinates in the nasal cavity. The turbulence caused by this disruption slows the air and directs it toward the olfactory epithelium. At the surface of the olfactory epithelium, odor molecules carried by the air contact olfactory receptor neurons which transduce the features of the molecule into non painful electrical impulses in the brain.

In cetaceans, the nose has been reduced to the nostrils, which have migrated to the top of the head, producing a more streamlined body shape and the ability to breathe while mostly submerged. Conversely, the elephant‘s nose has become elaborated into a long, muscular, manipulative organ called the trunk.

• Human nose
• Nasal bridge
• Nose-picking

ar:أنف an:Naso bs:Nos br:Fri bg:Нос (анатомия) ca:Nas cs:Nos cy:Trwyn da:Næse de:Nase dv:ނޭފަތް et:Nina el:Μύτη eo:Nazo eu:Sudur fa:بینی gd:Sròn ko:코 hr:Nos io:Nazo id:Hidung iu:ᕿᖓᖅ/qingaq it:Naso (anatomia) he:אף ku:Poz la:Nasus lt:Nosis jbo:nazbi hu:Orr mk:Нос ml:മൂക്ക് ms:Hidung nl:Neus no:Nese oc:Nas qu:Sinqa sq:Hunda scn:Nasu (anatumìa) simple:Nose sk:Nos sl:Nos fi:Nenä sv:Näsa tl:Ilong tg:Бинӣ uk:Ніс fiu-vro:Nõna yi:נאז zh-yue:鼻 diq:Pırnıke Template:Jb1 Template:WH Template:WS

Template:WikiDoc Cardiology News Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The circulatory system (or cardiovascular system) is an organ system that moves nutrients, gases, and wastes to and from cells, and helps stabilize body temperature and pH to maintain homeostasis. While humans, as well as other vertebrates have a closed circulatory system, some invertebrate groups have open circulatory system. The most primitive animal phyla lack circulatory systems.

The main components of the human circulatory system are the heart, the blood, and the blood vessels.

Furthermore, these components can either belong to the systemic circulation and the pulmonary circulation. The systemic circulation is the main part of the circulatory system, while the pulmonary system oxygenates the blood.

Systemic circulation is the portion of the cardiovascular system which carries oxygenated blood away from the heart, to the body, and returns deoxygenated blood back to the heart.

In the systemic circulation, arteries bring oxygenated blood to the tissues. As blood circulates through the body, oxygen diffuses from the blood into cells surrounding the capillaries, and carbon dioxide diffuses into the blood from the capillary cells. Veins bring deoxygenated blood back to the heart.

The release of oxygen from red blood cells or erythrocytes is regulated in mammals. It increases with an increase of carbon dioxide in tissues, an increase in temperature, or a decrease in pH. Such characteristics are exhibited by tissues undergoing high metabolism, as they require increased levels of oxygen.

Pulmonary circulation is the portion of the cardiovascular system which carries oxygen-depleted blood away from the heart, to the lungs, and returns oxygenated blood back to the heart.

De-oxygenated blood enters the right atrium of the heart and flows into the right ventricle where it is pumped through the pulmonary arteries to the lungs. Pulmonary veins return the now oxygen-rich blood to the heart, where it enters the left atrium before flowing into the left ventricle. From the left ventricle the oxygen-rich blood is pumped out via the aorta, and on to the rest of the body.

In the heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left ventricle, right atrium and right ventricle.

The circulatory systems of humans is closed, meaning that the blood never leaves the system of blood vessels. In contrast, oxygen and nutrients diffuse across the blood vessel layers and enters interstitial fluid, which carries oxygen and nutrients to the target cells, and carbon dioxide and wastes in the opposite direction.

The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms) and cephalopods (squid and octopus) are closed, just as in humans. Still, the systems of fish, amphibians, reptiles, and birds show various stages of the evolution of the circulatory system.

In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues. This is known as single circulation. The heart of fish is therefore only a single pump (consisting of two chambers). In amphibians and most reptiles, a double circulatory system is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart.

Birds and mammals show complete separation of the heart into two pumps, for a total of four heart chambers; it is thought that the four-chambered heart of birds evolved independently from that of mammals.

The open circulatory system is an arrangement of internal transport present in animals such as molluscs and arthropods, in which fluid (called hemolymph) in a cavity called the hemocoel bathes the organs directly and there is no distinction between blood and interstitial fluid; this combined fluid is called hemolymph or haemolymph. Muscular movements by the animal during locomotion can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the heart relaxes, blood is drawn back toward the heart through open-ended pores.

Hemolymph fills all of the interior hemocoel of the body and surrounds all cells. Hemolymph is composed of water, inorganic salts (mostly Na⁺, Cl^–, K⁺, Mg²⁺, and Ca²⁺), and organic compounds (mostly carbohydrates, proteins, and lipids). The primary oxygen transporter molecule is hemocyanin.

There are free-floating cells, the hemocytes, within the hemolymph. They play a role in the arthropod immune system.

Circulatory systems are absent in some animals, including flatworms (phylum Platyhelminthes). Their body cavity has no lining or enclosed fluid. Instead a muscular pharynx leads to an extensively branched digestive system that facilitates direct diffusion of nutrients to all cells. The flatworm’s dorso-ventrally flattened body shape also restricts the distance of any cell from the digestive system or the exterior of the organism. Oxygen can diffuse from the surrounding water into the cells, and carbon dioxide can diffuse out. Consequently every cell is able to obtain nutrients, water and oxygen without the need of a transport system.

• Electrocardiogram
• Sphygmomanometer
• Pulse meter
• Stethoscope
• Pulse

The valves of the heart were discovered by a physician of the Hippocratean school around the 4th century BC. However their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for transport of air.

Herophilus distinguished veins from arteries but thought that the pulse was a property of arteries themselves. Erasistratus observed that arteries that were cut during life bleed. He ascribed the fact to the phenomenon that air escaping from an artery is replaced with blood that entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood.

The 2nd century AD Greek physician, Galen knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart’s motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves.

Galen believed that the arterial blood was created by venous blood passing from the left ventricle to the right by passing through ‘pores’ in the interventricular septum, air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created ‘sooty’ vapors were created and passed to the lungs also via the pulmonary artery to be exhaled.

In 1242 the Arab physician Ibn al-Nafis became the first person to accurately describe the process of blood circulation in the human body, including pulmonary circulation. He stated:

“…the blood from the right chamber of the heart must arrive at the left chamber but there is no direct pathway between them. The thick septum of the heart is not perforated and does not have visible pores as some people thought or invisible pores as Galen thought. The blood from the right chamber must flow through the vena arteriosa (pulmonary artery) to the lungs, spread through its substances, be mingled there with air, pass through the arteria venosa (pulmonary vein) to reach the left chamber of the heart and there form the vital spirit…”

Contemporary drawings of this process have survived. In 1552, Michael Servetus described the same, and Realdo Colombo proved the concept, but it remained largely unknown in Europe.

Finally William Harvey, a pupil of Hieronymus Fabricius (who had earlier described the valves of the veins without recognizing their function), performed a sequence of experiments and announced in 1628 the discovery of the human circulatory system as his own and published an influential book about it. This work with its essentially correct exposition slowly convinced the medical world. Harvey was not able to identify the capillary system connecting arteries and veins; these were later described by Marcello Malpighi.

• Cardiology
• Lymphatic system
• Noise health effects
• Blood vessels
• Innate heat
• Cardiac muscle
• Major systems of the human body
• Heart
• Amato Lusitano
• William Harvey

• Iskandar, Albert Z. “Comprehensive Book on the Art of Medicine by Ibn al-Nafis”. Retrieved May 2, 2005.
• Nie Jing-bao, ” Refutation of the Claim that the Ancient Chinese described the Circulation of Blood,” New Zealand Journal of Asian Studies 3, 2 (December, 2001): 119-135

• The Circulatory System, a comprehensive overview
• The InVision Guide to a Healthy Heart An interactive website
• NCP Cardiovascular Medicine A Journal Covering Clinical Cardiovascular Medicine

Template:Organ systems

Template:Development of circulatory system

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ar:جهاز الدوران ast:Sistema cardiovascular bn:সংবহন তন্ত্র zh-min-nan:Sûn-khoân hē-thóng bs:Krvotok bg:Кръвообращение ca:Sistema cardiovascular cs:Oběhová soustava de:Blutkreislauf dv:ލޭދައުރުކުރާ ނިޒާމް eo:Kardiovaskula sistemo eu:Zirkulazio-aparatu gl:Aparello circulatorio hr:Krvožilni sustav id:Sistem kardiovaskular is:Blóðrásarkerfi it:Apparato circolatorio he:מחזור הדם pam:Circulatory system ku:Sîstema gera xwînê lv:Asinsrites orgānu sistēma lt:Kraujotakos sistema hu:Keringési rendszer mk:Циркулаторен систем nl:Hart- en vaatstelsel no:Sirkulasjonssystem nn:Kretsløpssystem qu:Sirk’a llika sq:Sistemi i qarkullimit të gjakut simple:Circulatory system sk:Obehová sústava sr:Крвни систем fi:Verenkierto sv:Kardiovaskulära systemet th:ระบบไหลเวียนโลหิต yi:בלוט צירקולאציע

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Blood is a specialized biological fluid consisting of red blood cells (also called RBCs or erythrocytes), white blood cells (also called leukocytes) and platelets (also called thrombocytes) suspended in a complex fluid medium known as blood plasma.

By far the most abundant cells in blood are red blood cells. These contain hemoglobin which gives blood its red color. The iron-containing heme portion of Hemoglobin facilitates hemoglobin-bound transportation of oxygen and carbon dioxide by selectively binding to these respiratory gasses and greatly increasing their solubility in blood. White blood cells help to resist infections, and platelets are important in the clotting of blood.

Blood is circulated around the body through blood vessels by the pumping action of the heart. Blood is pumped from the strong left ventricle of the heart through arteries to peripheral tissues and returns to the right atrium of the heart through veins, blood then enters the right ventricle and is pumped through the pulmonary artery to the lungs and returns to the left atrium through the pulmonary veins, blood then enters the left ventricle to be circulated again. Arterial blood carries oxygen from inhaled air in the lungs to all of the cells of the body, and venous blood carries carbon dioxide, produced as a waste product of metabolism by cells, to the lungs to be exhaled.

Medical terms related to blood often begin with hemo- or hemato- (BE: haemo- and haemato-) from the Greek word “haima” for “blood.” Anatomically, blood is considered a connective tissue from both its origin in the bones and its function.

• Supply of oxygen to tissues (bound to hemoglobin which is carried in red cells)
• Supply of nutrients such as glucose, amino acids and fatty acids (dissolved in the blood or bound to plasma proteins)
• Removal of waste such as carbon dioxide, urea and lactic acid
• Immunological functions, including circulation of white cells, and detection of foreign material by antibodies
• Coagulation, which is one part of the body’s self-repair mechanism
• Messenger functions, including the transport of hormones and the signalling of tissue damage
• Regulation of body pH (the normal pH of blood is in the range of 7.35 – 7.45)
• Regulation of core body temperature
• Hydraulic functions

Problems with blood composition or circulation can lead to downstream tissue dysfunction. The term ischaemia refers to tissue which is inadequately perfused with blood.

The blood is circulated around the lungs and body by the pumping action of the heart. Additional return pressure may be generated by gravity and the actions of skeletal muscles. In mammals, blood is in equilibrium with lymph, which is continuously formed from blood (by capillary ultrafiltration) and returned to the blood (via the thoracic duct). The lymphatic circulation may be thought of as the “second circulation”.

Blood accounts for 7% of the human body weight^[1], with an average density of approximately 1060 kg/m³, very close to pure water’s density of 1000 kg/m^3[2] The average adult has a blood volume of roughly 5 litres, composed of plasma (see below) and several kinds of cells (occasionally called corpuscles); these formed elements of the blood are erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets). The red blood cells constitute about 45% of whole blood by volume.

Each litre of blood contains:^[1]

• 5 × 10¹² erythrocytes (45.0% of blood volume) : In mammals, mature red blood cells lack a nucleus and organelles. They contain the blood’s hemoglobin and distribute oxygen. The red blood cells (together with endothelial vessel cells and some other cells) are also marked by glycoproteins that define the different blood types. The proportion of blood occupied by red blood cells is referred to as the hematocrit. The combined surface area of all the red cells in the human body would be roughly 2,000 times as great as the body’s exterior surface.^[3]
• 9 × 10⁹ leukocytes (1.0% of blood volume) : White blood cells are part of the immune system; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (pathogens) and foreign substances.
• 3 × 10¹¹ thrombocytes (<1.0% of blood volume) : Platelets are responsible for blood clotting (coagulation). They change fibrinogen into fibrin. This fibrin creates a mesh onto which red blood cells collect and clot. This clot stops more blood from leaving the body and also helps to prevent bacteria from entering the body.

The other 55% (making up a total of 2.7-3.0 litres in an average human) is blood plasma, a fluid that is the blood’s liquid medium, appearing golden-yellow in color. Blood plasma is essentially an aqueous solution containing 92% water, 8% blood plasma proteins, and trace amounts of other materials. Some components are:

• Serum albumin
• Blood clotting factors (to facilitate coagulation)
• Immunoglobulins (antibodies)
• Hormones
• Carbon dioxide
• Various other proteins
• Various electrolytes (mainly sodium and chloride)

Together, plasma and cells form a non-Newtonian fluid whose flow properties are uniquely adapted to the architecture of the blood vessels. The term serum refers to plasma from which the clotting proteins have been removed. Most of the protein remaining is albumin and immunoglobulins.

The normal pH of human arterial blood is approximately 7.40 (normal range is 7.35-7.45), a weak alkaline solution. Blood that has a pH below 7.35 is considered overly acidic, while blood pH above 7.45 is too alkaline. Blood pH along with arterial carbon dioxide tension (PaCO₂) and HCO₃ readings are helpful in determining the acid-base balance of the body. The respiratory system and urinary system normally control the acid-base balance of blood as part of homeostasis.

Blood cells are produced in the bone marrow; this process is termed hematopoiesis. The proteinaceous component (including clotting proteins) is produced overwhelmingly in the liver, while hormones are produced by the endocrine glands and the watery fraction is regulated by the hypothalamus and maintained by the kidney and indirectly by the gut.

Blood cells are degraded by the spleen and the Kupffer cells in the liver. The liver also clears some proteins, lipids and amino acids. The kidney actively secretes waste products into the urine. Healthy erythrocytes have a plasma half-life of 120 days before they are systematically replaced by new erythrocytes created by the process of hematopoiesis.

Blood oxygenation is measured in several ways, but the most important measure is the hemoglobin (Hb) saturation percentage. This is a non-linear (sigmoidal) function of the partial pressure of oxygen. About 98.5% of the oxygen in a sample of arterial blood in a healthy human breathing air at normal pressure is chemically combined with the Hb. Only 1.5% is physically dissolved in the other blood liquids and not connected to Hb. The hemoglobin molecule is the primary transporter of oxygen in mammals and many other species (for exceptions, see below).

With the exception of pulmonary and umbilical arteries and their corresponding veins, arteries carry oxygenated blood away from the heart and deliver it to the body via arterioles and capillaries, where the oxygen is consumed; afterwards, venules and veins carry deoxygenated blood back to the heart.

Differences in infrared absorption between oxygenated and deoxygenated blood form the basis for realtime oxygen saturation measurement in hospitals and ambulances.

Under normal conditions in humans at rest, hemoglobin in blood leaving the lungs is about 98-99% saturated with oxygen. In a healthy adult at rest, deoxygenated blood returning to the lungs is still approximately 75% saturated.^[4][5] Increased oxygen consumption during sustained exercise reduces the oxygen saturation of venous blood, which can reach less than 15% in a trained athlete; although breathing rate and blood flow increase to compensate, oxygen saturation in arterial blood can drop to 95% or less under these conditions.^[6] Oxygen saturation this low is considered dangerous in an individual at rest (for instance, during surgery under anesthesia): “As a general rule, any condition which leads to a sustained mixed venous saturation of less than 50% will be poorly tolerated and a mixed venous saturation of less than 30% should be viewed as a medical emergency.”^[7]

A fetus, receiving oxygen via the placenta, is exposed to much lower oxygen pressures (about 21% of the level found in an adult’s lungs) and so fetuses produce another form of hemoglobin with a much higher affinity for oxygen (hemoglobin F) in order to function under these conditions.^[8]

Substances other than oxygen can bind to the hemoglobin; in some cases this can cause irreversible damage to the body. Carbon monoxide for example is extremely dangerous when absorbed into the blood. When combined with the hemoglobin, it irreversibly makes carboxyhemoglobin which reduces the volume of oxygen that can be carried in the blood. This can very quickly cause suffocation, as oxygen is vital to many organisms (including humans). This damage can occur when smoking a cigarette (or similar item) or in event of a fire. Thus carbon monoxide is considered far more dangerous than the actual fire itself because it reduces the oxygen carrying content of the blood.

In insects, the blood (more properly called hemolymph) is not involved in the transport of oxygen. (Openings called tracheae allow oxygen from the air to diffuse directly to the tissues). Insect blood moves nutrients to the tissues and removes waste products in an open system.

Other invertebrates use respiratory proteins to increase the oxygen carrying capacity. Hemoglobin is the most common respiratory protein found in nature. Hemocyanin (blue) contains copper and is found in crustaceans and mollusks. It is thought that tunicates (sea squirts) might use vanabins (proteins containing vanadium) for respiratory pigment (bright green, blue, or orange).

In many invertebrates, these oxygen-carrying proteins are freely soluble in the blood; in vertebrates they are contained in specialized red blood cells, allowing for a higher concentration of respiratory pigments without increasing viscosity or damaging blood filtering organs like the kidneys.

Giant tube worms have extraordinary hemoglobins that allow them to live in extraordinary environments. These hemoglobins also carry sulfides normally fatal in other animals.

When systemic arterial blood flows through capillaries, carbon dioxide diffuses from the tissues into the blood. Some carbon dioxide is dissolved in the blood. Some carbon dioxide reacts with hemoglobin and other proteins to form carbamino compounds. The remaining carbon dioxide is converted to bicarbonate and hydrogen ions through the action of RBC carbonic anhydrase. Most carbon dioxide is transported through the blood in the form of bicarbonate ions.

Some oxyhemoglobin loses oxygen and becomes deoxyhemoglobin. Deoxyhemoglobin has a much greater affinity for hydrogen ion (H⁺) than does oxyhemoglobin so it binds most of the hydrogen ions.

Blood circulation transports heat through the body, and adjustments to this flow are an important part of thermoregulation. Increasing blood flow to the surface (e.g. during warm weather or strenuous exercise) causes warmer skin, resulting in faster heat loss, while decreasing surface blood flow conserves heat.

The restriction of blood flow can also be used in specialized tissues to cause engorgement resulting in an erection of that tissue. Examples of this would occur in a mammalian penis, clitoris or nipple.

Another example of a hydraulic function is the jumping spider, in which blood forced into the legs under pressure causes them to straighten for a powerful jump.

In humans and other hemoglobin-using creatures, oxygenated blood is bright red. This is due to oxygenated iron-containing hemoglobin found in the red blood cells. Deoxygenated blood is a darker shade of red, which can be seen during blood donation and when venous blood samples are taken.

The blood of most molluscs, and some arthropods such as horseshoe crabs, is blue. This is a result of its high content of copper-based hemocyanin instead of the iron-based hemoglobin found, for example, in mammals. While mammalian blood is never blue, there is a rare condition (sulfhemoglobinemia) that results in green blood. Skinks in the genus Prasinohaema have green blood due to a buildup of the waste product biliverdin.

Hippocratic medicine considered blood one of the four humors (together with phlegm, yellow bile and black bile). As many diseases were thought to be due to an excess of blood, bloodletting and leeching were a common intervention until the 19th century (it is still used for some rare blood disorders).

In classical Greek medicine, blood was associated with air, springtime, and with a merry and gluttonous (sanguine) personality. It was also believed to be produced exclusively by the liver.

Blood pressure and blood tests are amongst the most commonly performed diagnostic investigations that directly concern the blood.

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Problems with blood circulation and composition play a role in many diseases.

• Wounds can cause major blood loss (see bleeding). The thrombocytes cause the blood to coagulate, blocking relatively minor wounds, but larger ones must be repaired at speed to prevent exsanguination. Damage to the internal organs can cause severe internal bleeding, or hemorrhage.
• Circulation blockage can also create many medical conditions from ischemia in the short term to tissue necrosis and gangrene in the long term.
• Hemophilia is a genetic illness that causes dysfunction in one of the blood’s clotting mechanisms. This can allow otherwise inconsequential wounds to be life-threatening, but more commonly results in hemarthrosis, or bleeding into joint spaces, which can be crippling.
• Leukemia is a group of cancers of the blood-forming tissues.
• Major blood loss, whether traumatic or not (e.g. during surgery), as well as certain blood diseases like anemia and thalassemia, can require blood transfusion. Several countries have blood banks to fill the demand for transfusable blood. A person receiving a blood transfusion must have a blood type compatible with that of the donor.
• Overproduction of red blood cells is called polycythemia.
• Blood is an important vector of infection. HIV, the virus which causes AIDS, is transmitted through contact between blood, semen, or the bodily secretions of an infected person. Hepatitis B and C are transmitted primarily through blood contact. Owing to blood-borne infections, bloodstained objects are treated as a biohazard.
• Bacterial infection of the blood is bacteremia or sepsis. Viral Infection is viremia. Malaria and trypanosomiasis are blood-borne parasitic infections.

Blood transfusion is the most direct therapeutic use of blood. It is obtained from human donors by blood donation. As there are different blood types, and transfusion of the incorrect blood may cause severe complications, crossmatching is done to ascertain the correct type is transfused.

Other blood products administered intravenously are platelets, blood plasma, cryoprecipitate and specific coagulation factor concentrates.

Many forms of medication (from antibiotics to chemotherapy) are administered intravenously, as they are not readily or adequately absorbed by the digestive tract.

As stated above, some diseases are still treated by removing blood from the circulation, eg. haemochromatosis.

It is the fluid part of the blood that saves lives where severe blood loss occurs, other preparations can be given such as ringers atopical plasma volume expander as a non-blood alternative, and these alternatives where used are rivalling blood use when used.

• Blood substitutes often called Artificial blood
• List of human blood components
• blood phobia
• Medical technologist

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The digestive system is the organ system that breaks down and absorbs nutrients that are essential for growth and maintenance.

The digestive system includes the mouth, esophagus, stomach, pancreas, liver, gallbladder, duodenum, jejunum, ileum, (intestines), rectum, and anus.

This page contains links to all the parts of the digestive system.

• Overview at Colorado State University

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

The urinary system is the organ system that produces, stores, and eliminates urine. In humans it includes two kidneys, two ureters, the bladder, and the urethra. The analogous organ in invertebrates is the nephridium (in animals).

Typically, every human has two kidneys. The kidneys are bean-shaped organs about the size of a bar of soap. The kidneys lie in the abdomen, posterior or retroperitoneal to the organs of digestion, around or just below the ribcage and close to the lumbar spine. The kidneys are surrounded by what is called peri-nephric fat, and situated on the superior pole of each kidney is an adrenal gland. The kidneys receive their blood supply of 1.25 L/min (25% of the cardiac output) from the renal arteries which are fed by the Abdominal aorta. This is important because the kidneys’ main role is to filter water soluble waste products from the blood. The other attachment of the kidneys are at their functional endpoints the ureters, which lies more medial and runs down to the trigone of the bladder.

Functionally the kidney performs a number of tasks. In its role in the urinary system it concentrates urine, plays a crucial role in regulating electrolytes, and maintains acid-base homeostasis. The kidney excretes and re-absorbs electrolytes (e.g. sodium, potassium and calcium) under the influence of local and systemic hormones. pH balance is regulated by the excretion of bound acids and ammonium ions. In addition, they remove urea, a nitrogenous waste product from the metabolism of proteins from amino acids. The end point is a hyperosmolar solution carrying waste for storage in the bladder prior to urination.

Humans produce about 1.5 liters of urine over 24 hours, although this amount may vary according to circumstances. Because the rate of filtration at the kidney is proportional to the glomerular filtration rate, which is in turn related to the blood flow through the kidney, changes in body fluid status can affect kidney function. Hormones exogenous and endogenous to the kidney alter the amount of blood flowing through the glomerulus. Some medications interfere directly or indirectly with urine production. Diuretics achieve this by altering the amount of absorbed or excreted electrolytes or osmalites, which causes a diuresis.

The urinary bladder is a hollow muscular organ shaped like a balloon. It is located in the anterior pelvis. The bladder stores urine; it swells into a round shape when it is full and gets smaller when empty. In the absence of bladder disease, it can hold up to 500 mL (17 fl. oz.) of urine comfortably for two to five hours. The epithelial tissue associated with the bladder is called transitional epithelium. It allows the bladder to stretch to accommodate urine without rupturing the tissue.

Normally the bladder is sterile.

Sphincters (circular muscles) regulate the flow of urine from the bladder. The bladder itself has a muscular layer (detrusor muscle) that, when contracted, increases pressure on the bladder and creates urinary flow.

Urination is a conscious process, generally initiated by stretch receptors in the bladder wall which signal to the brain that the bladder is full. This is felt as an urge to urinate. When urination is initiated, the sphincter relaxes and the detrusor muscle contracts, producing urinary flow.

The endpoint of the urinary system is the urethra. Typically the urethra in humans is colonised by commensal bacteria below the external urethral sphincter. The urethra emerges from the end of the penis in males and between the clitoris and vagina in females.

Kidney diseases are normally investigated and treated by nephrologists, while the specialty of urology deals with problems in the other organs. Gynecologists may deal with problems of incontinence in women.

Diseases of other bodily systems also have a direct effect on urogenital function. For instance it has been shown that protein released by the kidneys in diabetes mellitus sensitises the kidney to the damaging effects of hypertension^[1].

Diabetes also can have a direct effect in micturition due to peripheral neuropathies which occur in some individuals with poorly controlled diabetics.

Renal failure is defined by functional impairment of the kidney. Renal failure can be acute or chronic, and can be further broken down into categories of pre-renal, intrinsic renal and post-renal.

Pre-renal failure refers to impairment of supply of blood to the functional nephrons including renal artery stenosis. Intrinsic renal diseases are the classic diseases of the kidney including drug toxicity and nephritis. Post-renal failure is outlet obstruction after the kidney, such as a renal stone or prostatic bladder outlet obstruction.

Renal failure may require medication, dietary and lifestyle modification and dialysis.

Primary renal cell carcinomas as well as metastatic cancers can affect the kidney.

The causes of diseases of the body are common to the urinary tract. Structural and or traumatic change can lead to hemorrhage, functional blockage or inflammation. Colonisation by bacteria, protozoa or fungi can cause infection. Uncontrolled cell growth can cause neoplasia.

For example:

• Urinary tract infections (UTIs), interstitial cystitis
• incontinence (involuntary loss of urine), benign prostatic hyperplasia (where the prostate overgrows), prostatitis (inflammation of the prostate).
• Transitional cell carcinoma (bladder cancer), renal cell carcinoma (kidney cancer), and prostate cancer are examples of neoplasms affecting the urinary system.

The term “uropathy” refers to a disease of the urinary tract, while “nephropathy” refers to a disease of the kidney.

Biochemical blood tests determine the amount of typical markers of renal function in the blood serum, for instance serum urea and serum creatinine. Biochemistry can also be used to determine serum electrolytes. Special biochemical tests (arterial blood gas) can determine the amount of dissolved gases in the blood, indicating if pH imbalances are acute or chronic.

Urinalysis is a test that studies the content of urine for abnormal substances such as protein or signs of infection.

• A Full Ward Test, also known as dipstick urinalysis, involves the dipping of a biochemically active test strip into the urine specimen to determine levels of tell-tale chemicals in the urine.
• Urinalysis can also involve MC&S microscopy , culture and sensitivity

Urodynamic tests evaluate the storage of urine in the bladder and the flow of urine from the bladder through the urethra. It may be performed in cases of incontinence or neurological problems affecting the urinary tract.

Ultrasound is commonly performed to investigate problems of the kidney and/or urinary tract.

Radiology:

• KUB is plain radiography of the urinary system, e.g. to identify kidney stones.
• An intravenous pyelogram studies the shape of the urinary system.
• CAT scans and MRI can also be useful in localising urinary tract pathology.

• Urothelium
• Major systems of the human body

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The human male reproductive system is a series of organs located outside of the body and around the pelvic region of a male that contribute towards the reproductive process.

The male contributes to reproduction by producing spermatozoa. The spermatozoa then fertilize the egg in the female body and the fertilized egg (zygote) gradually develops into a fetus, which is later born as a child.

The testes hang outside the abdominal cavity of the male within the scrotum. They begin their development in the abdominal cavity but descend into the scrotal sacs during the last 2 months of fetal development. This is required for the production of sperm because internal body temperatures are too high to produce viable sperm.

In the body of an average male, there are two testicles located in a sac called the scrotum. On top of these organs is the epididymis, the “housing area” for sperm that has been produced. The tightly coiled epididymis (6 meters or 20 feet when unraveled) store sperm cells for up to 4 weeks, while they are learning to swim.

The penis has a long shaft and enlarged tip called the glans penis. The penis is the copulatory organ of the males. When the male is sexually aroused, the penis becomes erect and ready for intercourse. Erection is achieved because blood sinuses within the erectile tissue of the penis become filled with blood. The arteries of the penis are dilated while the veins are passively compressed so that blood flows into the erectile cartilage under pressure. The male penis is made of two different tissues, soft spongey tissue and cartilage. is a pelvic bone in the front top of the penis.

A mature spermatoza, or spermatozoon, has 3 distinct parts: a head, a mid-piece, and a tail. The tail is made up of microtubules that form cilia and flagella, and the mid-piece contains energy-producing mitochondria. The head contains 23 chromosomes within a nucleus. The tip of the nucleus is covered by a cap called the acrosome, which is believed to contain enzymes needed to breach the egg for fertilization. A normal human male usually produces several hundred million sperm per day. Sperm are continually produced throughout a male’s reproductive life, though production decreases with age.

During ejaculation, sperm leaves the penis in a fluid called seminal fluid. This fluid is produced by 3 types of glands, the seminal vesicles, the prostate gland, and Cowper’s glands (bulbourethral glands). Each component of a seminal fluid has a particular function. Sperm are more viable in a basic solution, so seminal fluid has a slightly basic pH. Seminal fluid also acts as an energy source for the sperm, and contains chemicals that cause the uterus to contract.There is a tiny gland that holds sperm.

• “What are the contents of semen?” at for-men-only-magazine.com

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The human female reproductive system contains two main parts: the vagina and uterus, which act as the receptacle for the male’s sperm, and the ovaries, which produce the female’s ova. All of these parts are always internal; the vagina meets the outside at the vulva, which also includes the labia, clitoris and urethra. The vagina is attached to the uterus through the cervix, while the uterus is attached to the ovaries via the Fallopian tubes. At certain intervals, the ovaries release an ovum, which passes through the fallopian tube into the uterus.

If, in this transit, it meets with sperm, the sperm penetrate and merge with the egg, fertilizing it. The fertilization usually occurs in the oviducts, but can happen in the uterus itself. The zygote then implants itself in the wall of the uterus, where it begins the processes of embryogenesis and morphogenesis. When developed enough to survive outside the womb, the cervix dilates and contractions of the uterus propel the fetus through the birth canal, which is the vagina.

The ova are larger than sperm and are generally all created by birth. Approximately every month, a process of oogenesis matures one ovum to be sent down the Fallopian tube attached to its ovary in anticipation of fertilization. If not fertilized, this egg is flushed out of the system through menstruation.

The vagina is the tubular tract leading from the uterus to the exterior of the body in female mammals, or to the cloaca in female birds and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the oviduct.

The vagina is the place where semen from the man is deposited into the woman’s body during sexual intercourse.

The cervix is the lower, narrow portion of the uterus where it joins with the top end of the vagina. It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall. Approximately half its length is visible; the remainder lies above the vagina beyond view.

The uterus or womb is the major female reproductive organ of humans. One end, the cervix, opens into the vagina; the other is connected on both sides to the fallopian tubes.

The uterus mostly consists of muscle, known as myometrium. Its major function is to accept a fertilized ovum which becomes implanted into the endometrium, and derives nourishment from blood vessels which develop exclusively for this purpose. The fertilized ovum becomes an embryo, develops into a fetus and gestates until childbirth.

The Fallopian tubes or oviducts are two very fine tubes leading from the ovaries of female mammals into the uterus.

On maturity of an ovum, the follicle and the ovary’s wall rupture, allowing the ovum to escape and enter the Fallopian tube. There it travels toward the uterus, pushed along by movements of cilia on the inner lining of the tubes. This trip takes hours or days. If the ovum is fertilized while in the Fallopian tube, then it normally implants in the endometrium when it reaches the uterus, which signals the beginning of pregnancy.

The ovaries are the place inside the female body where ova or eggs are produced. The process by which the ovum is released is called ovulation. The speed of ovulation is periodic and impacts directly to the length of a menstrual cycle.

After ovulation, the ovum is captured by the oviduct, where it travelled down the oviduct to the uterus, occasionally being fertilised on its way by an incoming sperm, leading to pregnancy.

The Fallopian tubes are often called the oviducts and they have small hairs (cilia) to help the egg cell travel.

• OBGYN.net – Obstetrics, Gynaecology, Infertility, Pregnancy, Birth, & Women’s Health top online resource

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Obstetrics (from the Latin obstare, “to stand by”) is the surgical specialty dealing with the care of a woman and her offspring during pregnancy, childbirth and the puerperium (the period shortly after birth). Midwifery is the equivalent non-surgical specialty. Most obstetricians are also gynaecologists. See Obstetrics and gynaecology.

The average gestational period for humans is 40 weeks by gestational age and 38 weeks by fertilization age. This is divided into three trimesters.

In obstetric practice, an obstetrician or midwife sees a pregnant woman on a regular basis to check the progress of the pregnancy, to verify the absence of ex-novo disease, to monitor the state of preexisting disease and its possible effect on the ongoing pregnancy. A woman’s schedule of antenatal appointment varies according to the presence of risk factors, such as diabetes, and local resources.

Some of the clinically and statistically more important risk factors that must be systematically excluded, especially in advancing pregnancy, are pre-eclampsia, abnormal placentation, abnormal fetal presentation and Intrauterine Growth Retardation.

For example, to identify pre-eclampsia, blood-pressure and albuminuria (level of urine protein) are checked at every opportunity.

Placenta praevia must be excluded (PP = low lying placenta that, at least partially, obstructs the birth canal and therefore warrants elective caesarean delivery); this can only be achieved with the use of an ultrasound scan.

In late pregnancy fetal presentation must be established: cepfalic presentation (head first) is the norm but the fetus may present feet-first or buttocks-first (breech), side-on (transverse), or at an angle (oblique presentation).

Intrauterine Growth Retardation is a general designation, where the fetus is smaller than expected when compared to its gestational age (in this case fetal growth parameters show a tendency to drop off from the 50th percentile eventually falling below the 10th percentile, when plotted on a fetal growth chart). Causes can be intrinsic (to the fetus) or extrinsic (maternal or placental problems).

First trimester: elevated β-hCG (human chorionic gonadotrophin) of up to 100,000 mIU/mL by 10 weeks GA is thought to contribute to morning sickness, fatigue, mood swings and food cravings. The symptoms can last through 12 to 16 weeks of gestation.

Second trimester: The abdomen shows an obvious swelling arising from the pelvis, starting the “obvious phase” of pregnancy. Hyperpigmentation, including linea nigra, may appear.

Third trimester: The mother may experience backaches due to increased strain. Typically, the curvature of the spine is changed as pregnancy evolves in order to counteract the change in weight distribution. The mother may also suffer mild urinary incontinence due to pressure on the bladder by the pregnant uterus, as well as heartburn(due to compression of the stomach).

• Bluish discoloration of vagina and cervix (Chadwick’s sign)
• Softening and cyanosis of cervix after 4 weeks (Goodell’s sign)
• Softening of uterus after 6 weeks (Hegar’s or Ladin’s sign)
• Breast swelling and tenderness
• Linea nigra from umbilicus to pubis
• Telangiectasias
• Palmar erythema
• Amenorrhea
• Nausea and vomiting
• Breast pain
• Fetal movement
• Sciatica (Pain caused by compression of the sciatic nerve)

During pregnancy, the woman undergoes many physiological changes, which are entirely normal, including cardiovascular, hematologic, metabolic, renal and respiratory changes that become very important in the event of complications.

The woman is the sole provider of nourishment for the embryo and later, the fetus, and so her plasma and blood volume slowly increase by 40-50% over the course of the pregnancy to accommodate the changes. This results in overall vasodilation, an increase in heart rate (15 beats/min more than usual), stroke volume, and cardiac output. Cardiac output increases by about 50%, mostly during the first trimester. The systemic vascular resistance also drops due to the smooth muscle relaxation caused by elevated progesterone, leading to a fall in blood pressure. Diastolic blood pressure consequently decreases between 12-26 weeks, and increases again to prepregnancy levels by 36 weeks. If the blood pressure remains abnormal beyond 36 weeks, the woman should be investigated for pre-eclampsia, a condition that precedes eclampsia.

• The plasma volume increases by 50% and the red blood cell volume increases only by 20-30%.
• Consequently, the hematocrit decreases.
• White blood cell count increases and may peak at over 20 mil/mL in stressful conditions.
• Decrease in platelet concentration to a minimal normal values of 100-150 mil/mL
• The pregnant woman also becomes hypercoagulable due to increased liver production of coagulation factors, mainly fibrinogen and factor VIII.

During pregnancy, both protein metabolism and carbohydrate metabolism are affected. One kilogram of extra protein is deposited, with half going to the fetus and placenta, and another half going to uterine contractile proteins, breast glandular tissue, plasma protein, and hemoglobin.

• Increased caloric requirement by 300 kcal/day
• Gain of 20 to 30 lb (10 to 15 kg)
• Increased protein requirement to 70 or 75 g/day
• Increased folate requirement from 0.4 to 0.8 mg/day (important in preventing neural tube defects)

All patients are advised to take prenatal vitamins to compensate for the increased nutritional requirements. The use of Omega 3 fatty acids supports mental and visual development of infants.^[1] Choline supplementation of research mammals supports mental development that lasts throughout life.^[2]

• nausea and vomiting (“morning sickness“) may be due to elevated Beta-hCG, which should resolve by 14 to 16 weeks
• prolonged gastric empty time
• decreased gastroesophageal sphincter tone, which can lead to acid reflux
• decreased colonic motility, which leads to increased water absorption and constipation

• Increase in kidney and ureter size
• Increased glomerular filtration rate (GFR) by 50%, which subsides around 20 weeks postpartum
  • Decreased BUN (blood urea nitrogen) and creatinine, and glucosuria (due to saturated tubular reabsorption)
    • Persistent glucosuria can suggest gestational diabetes
• Increased renin-angiotensin system, causing increased aldosterone levels
  • Plasma sodium does not change because this is offset by the increase in GFR

• Increased tidal volume (30-40%)
• Decreased total lung capacity (TLC) by 5% due to elevation of diaphragm from uteral compression
• Decreased expiratory reserve volume
• Increased minute ventilation (30-40%) which causes a decrease in PaCO2 and a compensated respiratory alkalosis

All of these changes can contribute to the dyspnea (shortness of breath) that a pregnant woman may experience.

• Increased estrogen, which is mainly produced in the placenta
  • Fetal well being is associated with maternal estrogen levels
  • Causes an increase in thyroxine-binding globulin (TBG)
• Increased human chorionic gonadotropin (β-hCG), which is produced by the placenta. This maintains progesterone production by the corpus luteum
• Human placental lactogen (hPL) is produced by the placenta and ensures nutrient supply to the fetus. It also causes lipolysis and is an insulin antagonist, which is a diabetogenic effect.
• Increased progesterone production, first by corpus luteum and later by the placenta. Its main course of action is to relax smooth muscle.
• Increased prolactin
• Increased alkaline phosphatase

• Lower back pain due to a shift in gravity
• Increased estrogen can cause spider angiomata and palmar erythema
• Increase melanocyte stimulating hormone (MSH) can cause hyperpigmentation of nipples, umbilicus, abdominal midline (linea nigra), perineum, and face (melasma or chloasma)

• Edema, or swelling, of the feet is common during pregnancy, partly because the enlarging uterus compresses veins and lymphatic drainage from the legs.

Prenatal care is important in screening for various complications of pregnancy. This includes routine office visits with physical exams and routine lab tests:

• complete blood count (CBC)
• blood type (blood transfusion may be needed in an emergency)
• general antibody screen (indirect Coombs test) for HDN
  • Rh D negative antenatal patients should receive RhoGam at 28 weeks to prevent Rh disease.
• Rapid plasma reagent (RPR) which screens for syphilis
• Rubella antibody screen
• Hepatitis B surface antigen
• Gonorrhea and Chlamydia culture
• PPD for tuberculosis
• Pap smear
• Urinalysis and culture
• HIV screen
• Group B Streptococcus screen — will receive IV penicillin if positive (if mother is allergic, alternative therapies include IV clindamycin or IV vancomycin)

• MSAFP/triple screen (maternal serum alpha-fetoprotein) – elevation correlated with neural tube defects and decrease correlated with Down’s syndrome
• ultrasound
• amniocentesis in older patients

• hematocrit (if low, mother will receive iron supplementation)
• Glucose loading test (OGTT, GLT, GTT) – screens for gestational diabetes; if > 140 mg/dL, a glucose tolerance test (GTT) is administered; a fasting glucose > 105 mg/dL suggests gestational diabetes.

See Complications of pregnancy

Common

• ultrasound is used for many functions:
  • Dating the gestational age of a pregnancy, most accurate in first trimester
  • Detecting fetal anomalies in the second trimester
  • biophysical profiles (BPP)
  • Blood flow velocity in umbilical cord — decrease/absence/reversal or diastolic blood flow in the umbilical artery is worrisome.
  • Congenital anomalies can be diagnosed with second trimester ultrasound
• Fetal karyotype for the screening of genetic diseases can be obtained via amniocentesis or chorionic villus sampling (CVS)

Uncommon

• Fetal hematocrit for the assessment of fetal anemia, Rh isoimmunization, or hydrops can be determined by percutaneous umbilical blood sampling (PUBS) which is done by placing a needle through the abdomen into the uterus and taking a portion of the umbilical cord.
• Fetal lung maturity is associated with how much surfactant the fetus is producing. Reduced production of surfactant indicates decreased lung maturity and is a high risk factor for neonatal respiratory distress syndrome (NRDS). Typically a lecithin:sphingomyelin ratio greater than 1.5 is associated with increased lung maturity.
• Nonstress test (NST) for fetal heart rate
• Oxytocin challenge test

Reasons to induce include:

1. pre-eclampsia
2. IUGR
3. diabetes
4. other general medical condition, such as renal disease
5. “postdates” – the pregnancy has lasted longer than 41 weeks after the last menstrual period

Induction may occur any time after 34 weeks of gestation if the risk to the fetus or mother is greater than the risk of delivering a premature fetus regardless of lung maturity.

If a woman does not eventually labour by 41-42 weeks, induction may be performed, as the placenta may become unstable after this date.

Induction may be achieved via several methods:

1. pessary of Prostin cream, prostaglandin E₂
2. iv. or oral administration of misoprostol
3. cervical insertion of a 30-mL Foley catheter
4. rupturing the amniotic membranes
5. intravenous infusion of synthetic oxytocin (Pitocin or Syntocinon)

During labor itself, the obstetrician may be called on to do a number of things:

1. monitor the progress of labor, by reviewing the nursing chart, performing vaginal examination, and assessing the trace produced by a fetal monitoring device (the cardiotocograph)
2. accelerate the progress of labor by infusion of the hormone oxytocin
3. provide pain relief, either by nitrous oxide (nowadays uncommon, at least in the U.S.), opiates, or by epidural anesthesia done by anaethestists, an anesthesiologist, or a nurse anesthetist.
4. surgically assisting labor, by forceps or the Ventouse (a suction cap applied to the fetus’ head)
5. Caesarean section, if vaginal delivery is decided against or appears too difficult. Caesarean section can either be elective, that is, arranged before labor, or decided during labor as an alternative to hours of waiting. True “emergency” Cesarean sections (where minutes count) are a rarity.

During the time immediately after birth both baby as well as mother are hormonally cued to bond, the mother through the release of oxytocin a hormone also released with breastfeeding.

Two main emergencies are ectopic pregnancy and (pre)eclampsia.

• Ectopic pregnancy is when an embryo implants in the Fallopian tube or (rarely) on the ovary or inside the peritoneal cavity. This may cause massive internal bleeding.

• Pre-eclampsia is a disease which is defined by a combination of signs and symptoms that are related to maternal hypertension. The cause is unknown, and markers are being sought to predict its development from the earlist stages of pregnancy.

Some unknown factors cause vascular damage in the [endothelium], causing hypertension and proteinuria. If severe, it progresses to fulminant pre-eclampsia, with headaches and visual disturbances. This is a prelude to eclampsia, where a convulsion occurs, which can be fatal.

In present society, medical science has developed a number of procedures to monitor pregnancy.

On the first visit to her obstetrician or midwife, the pregnant woman is asked to carry out the antenatal record, which constitutes a medical history and physical examination.

On subsequent visits, the gestational age (GA) is rechecked with each visit.

Symphysis-fundal height (SFH; in cm) should equal gestational age after 20 weeks of gestation, and the fetal growth should be plotted on a curve during the antenatal visits.

The fetus is palpated by the midwife or obstetrician using Leopold maneuver to determine the position of the baby. Blood pressure should also be monitored, and may be up to 140/90 in normal pregnancies. High blood pressure indicates hypertension and possibly pre-eclampsia, if severe swelling (edema) and spilled protein in the urine are also present.

Fetal screening is also used to help assess the viability of the fetus, as well as congenital problems. Genetic counseling is often offered for families who may be at an increased risk to have a child with a genetic condition.

Amniocentesis at around the 20th week is sometimes done for women 35 or older to check for Down’s Syndrome and other chromosome abnormalities in the fetus.

Even earlier than amniocentesis is performed, the mother may undergo the triple test, nuchal screening, nasal bone, alpha-fetoprotein screening and Chorionic villus sampling, also to check for disorders such as Down Syndrome. Amniocentesis is a prenatal genetic screening of the fetus, which involves inserting a needle through the mother’s abdominal wall and uterine wall, to extract fetal DNA from the amniotic fluid. There is a risk of miscarriage and fetal injury with amniocentesis because it involves penetrating the uterus with the baby still in utero.

Imaging is another important way to monitor a pregnancy. The mother and fetus are also usually imaged in the first trimester of pregnancy. This is done to predict problems with the mother; confirm that a pregnancy is present inside the uterus; guess the gestational age; determine the number of fetuses and placentae; evaluate for an ectopic pregnancy and first trimester bleeding; and assess for early signs of anomalies.

X-rays and computerized tomography (CT) are not used, especially in the first trimester, due to the ionizing radiation, which has teratogenic effects on the fetus. Instead, ultrasound is the imaging method of choice in the first trimester and throughout the pregnancy, because it emits no radiation, is portable, and allows for realtime imaging. Ultrasound imaging may be done at any time throughout the pregnancy, but usually happens at the 12th week (dating scan) and the 20th week (detailed scan).

A normal gestation would reveal a gestational sac, yolk sac, and fetal pole. The gestational age can be assessed by evaluating the mean gestation sac diameter (MGD) before week 6, and the crown-rump length after week 6. Multiple gestation is evaluated by the number of placentae and amniotic sacs present.

Pregnancy has different cultural aspects related to the perception of the body, the relationship with partner and to the meaning of the event.

• embryo – conceptus between time of fertilization to 10 weeks of gestation
• fetus – from 10 weeks of gestation to time of birth
• infant – time of birth to 1 year of age
• gestational age – time from last menstrual period (LMP) up to present
• first trimester – up to 14 weeks of gestation
• second trimester – 14 to 28 weeks of gestation
• third trimester – 28 weeks to delivery
• viability – minimum age for fetus survival, ca. third trimester
• previable infant – delivered prior to 24 weeks
• preterm infant – delivered between 24-37 weeks
• term infant – delivered between 37-42 weeks
• gravidity (G) – number of times a woman has been pregnant
• parity (P) – number of pregnancies with a birth beyond 20 weeks GA or an infant weighing more than 500 g
• Ga Pw-x-y-z – a = number of pregnancies, w = number of term births, x = number of preterm births, y = number of abortions (spontaneous or therapeutic), z = number of living children; for example, G4P1-2-1-3 means the woman had a total of 4 pregnancies, of which 1 is of term, 2 are preterm, 1 miscarriage or therapeutic abortion, and 3 total living children (1 term + 2 preterm).

• List of obstetric topics
• Gynecology
• Home birth
• Maternal health
• Midwifery
• Obstetric ultrasonography
• Puerperium

• J Lane (July 1987). “A provincial surgeon and his obstetric practice: Thomas W. Jones of Henley-in-Arden, 1764–1846”. Medical History. 31 (3): 333&ndash, 348.

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The musculoskeletal system (also known as the locomotor system) is an organ system that gives animals the ability to physically move using the muscles and skeletal system.

The human musculoskeletal system consists of the human skeleton, made by bones attached to other bones with joints, and skeletal muscle attached to the skeleton by tendons.

Among others, cnidarians and annelids, have a hydrostatic skeleton similar to a water-filled balloon, these animals can move by contracting the muscles surrounding the fluid-filled pouch, creating pressure within the pouch that causes movement. Animals such as earthworms use their hydrostatic skeletons to change their body shape as they move forward, from long and skinny to short and stumpy. Arthropoda have their muscles attached to an exoskeleton.

In mammals, when a muscle contracts, a series of reactions occur. Muscle contraction is stimulated by the motor neuron sending a message to the muscles from the somatic nervous system. Depolarization of the motor neuron results in neurotransmitters being released from the nerve terminal. The space between the nerve teminal and the muscle cell is called the neuromuscular junction. These neurotransmitters diffuse across the synapse and bind to specific receptor sites on the sarcolemma (cell membrane of the muscle fiber). When enough receptors are stimulated, an action potential is generated and the permeability of the sarcolemma is altered. This process is known as initiation.

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In zootomy, the integumentary system is the external covering of the body, comprising the skin, hair, scales, nails, sweat glands and their products (sweat and mucus). The integumentary system has a variety of functions; in animals, it may serve to waterproof, cushion and protect the deeper tissues, excrete wastes, regulate temperature and is the location of sensory receptors for pain, pressure and temperature. The name derives from the Latin integumentum, which means ‘a covering’.