Medullary ray

The medullary ray is the middle part of the cortical lobule or renal lobule, consisting of a group of straight tubes to the collecting ducts.

Their name is potentially misleading — the “medullary” refers to their destination, not their location. They are located only in the renal cortex, and not in the renal medulla.^[1]

Medullary rays can also refer to a characteristic found in woods. In this context the term refers to radial sheets or ribbons extending vertically through the tree across and perpendicular to the growth rings. Also called pith rays or wood rays, these formations of primarily parenchyma cells allow the radial transmission of sap. In quartersawn material, where the wood is cut in to boards with the growth rings roughly perpendicular to the face of the board, the medullary rays often produce beautiful figure such as silver grain, medullary spots, pith flecks, etc.^[2]

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• Histology image: 16003loa – Histology Learning System at Boston University – “Urinary System: kidney, H&E, cortex and medullary ray”
• Histology image: 15901loa – Histology Learning System at Boston University – “Urinary System: neonatal kidney”
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