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Concept
Loop of Henle
Résumé
In the kidney, the loop of Henle (ˈhɛnli) (or Henle's loop, Henle loop, nephron loop or its Latin counterpart ansa nephroni) is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. Named after its discoverer, the German anatomist Friedrich Gustav Jakob Henle, the loop of Henle's main function is to create a concentration gradient in the medulla of the kidney.
By means of a countercurrent multiplier system, which uses electrolyte pumps, the loop of Henle creates an area of high urea concentration deep in the medulla, near the papillary duct in the collecting duct system. Water present in the filtrate in the papillary duct flows through aquaporin channels out of the duct, moving passively down its concentration gradient. This process reabsorbs water and creates a concentrated urine for excretion.
The loop of Henle can be divided into four parts:
Thin descending limb of loop of Henle
The thin descending limb has low permeability to ions and urea while being highly permeable to water. The loop has a sharp bend in the renal medulla going from descending to ascending thin limb.
Thin ascending limb of loop of Henle
The thin ascending limb is impermeable to water, but it is permeable to ions.
Ascending limb of loop of Henle
Sodium (Na+), potassium (K+) and chloride (Cl−) ions are reabsorbed from the urine by secondary active transport by a Na–K–Cl cotransporter (NKCC2). The electrical and concentration gradient drives more reabsorption of Na+, as well as other cations such as magnesium (Mg2+) and calcium (Ca2+).
Cortical thick ascending limb
The cortical thick ascending limb drains urine into the distal convoluted tubule.
The tissue type of the loop is simple squamous epithelium. The "thick" and "thin" terminology does not refer to the size of the lumen, but to the size of the epithelial cells. The loop is also sometimes called the nephron loop.
The loop of Henle is supplied by blood in a series of straight capillaries descending from the cortical efferent arterioles.
Source officielle
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