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 interlobar arteries. The
interlobar arteries each in turn branch into
arcuate arteries, which in turn branch to form
interlobular arteries, and these 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 and into the renal tubules. Flow continues through the renal tubules, including the
proximal tubule, the
Loop of Henle, through the
distal tubule and finally leaves the kidney by means of the
collecting duct, leading to the renal pelvis, the dilated portion of the
ureter.