The renal medulla is the darker inner region of the kidney, arranged as 8 to 18 cone-shaped renal pyramids. It contains the loops of Henle, the vasa recta and the collecting ducts. Its main job is to build a very salty environment that lets the kidney make concentrated urine.
| Location | Deep to the cortex, forming the renal pyramids whose tips (papillae) point toward the renal sinus |
|---|---|
| Parts |
|
| Nerve Supply | Renal plexus |
| Blood Supply | Arcuate arteries; Vasa recta (from efferent arterioles of juxtamedullary nephrons) |
| Venous drainage |
|
| Lymphatic drainage |
|
Creates an increasing salt concentration toward the papillae (the countercurrent system) that allows water to be drawn out of the collecting ducts to concentrate urine.
The medulla has a low oxygen supply, which makes it vulnerable to damage from reduced blood flow, some drugs and sickle cell disease. Painkiller overuse (especially combinations containing phenacetin) and diabetes can cause the papillae at the pyramid tips to die and slough off. Loss of medullary concentrating ability shows up early as passing large volumes of dilute urine, including at night.
A congenital widening of the collecting ducts in the medulla that predisposes to stones and infection.
The collecting ducts fail to respond to antidiuretic hormone, so the medulla cannot concentrate urine and large volumes of dilute urine are passed.
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