Library · Anatomy
Renal medulla
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The kidney has two distinct zones inside. The outer one is the cortex; the inner one, between the cortex and the renal sinus, which is the hollow center of the kidney, is the renal medulla. The medulla is not a uniform mass: it is organized into pyramids.
Medullary rays, strips that descend from the neighboring cortex, run inside those pyramids. Two structures travel there: the limbs of the loop of Henle, the hairpin-shaped stretch of the kidney, and the medullary collecting ducts, where the urine that has already formed gathers.
Each pyramid, along with the cortex covering it, forms a renal lobe; each kidney has around nine. The urine from each lobe leaves through the papilla, at the tip of the pyramid, and drains into a minor calyx. Each pyramid drains through its tip, like a funnel pointing inward.
In brief
The renal medulla occupies the kidney parenchyma between the outer cortex and the renal sinus, and is organized into pyramids.
Medullary rays run within the pyramids, descending from the cortex and carrying the limbs of the loop of Henle and the medullary collecting ducts.
Each pyramid with its cortex forms a renal lobe, about nine per kidney; urine leaves through a papilla at the apex into a minor calyx.
Each pyramid drains through its tip, like a funnel pointing inward.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingAnatomy, Abdomen and Pelvis: Kidneys, StatPearlsPublished
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