The renal medulla is the innermost part of the kidney. The renal medulla is split up into a number of sections, known as the renal pyramids. Blood enters into the kidney via the renal artery, which then splits up to form the arcuate arterioles. The arcuate arterioles each in turn branch into interlobar arterioles, which finally reach the glomeruli. At the glomerulus the blood reaches a highly disfavourable pressure gradient and a large exchange surface area, which forces the serum portion of the blood out of the vessel into the renal tubules. Flow continues through the renal tubules, including the proximal tubule, the Loop of Henle, and finally leaves the kidney by means of the collecting duct, leading to the renal urethra.
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