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In other words, the length of the loop of Henle limits the concentration of the gradient, i.e., the longer the loop, the greater the osmotic gradient. Thus, longer loops would allow for steeper gradients and greater capacity to concentrate urine. Through the countercurrent multiplier the loop of Henle increases the osmolarity of the medulla.
Also, the medullary interstitium is highly concentrated (because of the activity of the ascending limb), leading to a strong osmotic gradient from the descending limb to the medulla. Because of these factors, the concentration of the urine increases dramatically in the descending limb.
This allows for a countercurrent exchange system whereby the medulla becomes increasingly concentrated, but at the same time setting up an osmotic gradient for water to follow should the aquaporins of the collecting duct be opened by ADH.
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis.The collecting duct participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin (antidiuretic hormone).
The cortex and medulla of the kidney contain nephrons, [21] each of which consists of a glomerulus and a complex tubular system. [22] The cortex contains glomeruli and is responsible for filtering the blood. [7] The medulla is responsible for urine concentration [23] and contains tubules with short and long loops of Henle. [24]
The renal medulla (Latin: medulla renis 'marrow of the kidney') 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 segmental arteries which then branch to form interlobar arteries.
This is because sodium is reabsorbed in exchange for potassium and therefore causes only a modest change in the osmotic gradient between the blood and the tubular fluid. Furthermore, the epithelium of the distal convoluted tubules and collecting ducts is impermeable to water in the absence of antidiuretic hormone (ADH) in the blood.
The proximal tubule is the segment of the nephron in kidneys which begins from the renal pole of the Bowman's capsule to the beginning of loop of Henle.At this location, the glomerular parietal epithelial cells (PECs) lining bowman’s capsule abruptly transition to proximal tubule epithelial cells (PTECs).