Descending limb of loop of Henle

Diagram of a nephron, the functional unit of the kidney. The descending limb of the loop of Henle is labeled.

The Descending limb of loop of Henle is a segment of the nephron in the kidney. It is a thin tubule that extends from the proximal convoluted tubule and leads into the ascending limb of loop of Henle. This structure plays a crucial role in the concentration of urine, as part of the kidney's function in maintaining the body's water balance.

Structure

The descending limb of the loop of Henle is a thin-walled tube that descends into the renal medulla. It is permeable to water but not to ions, allowing water to be reabsorbed into the body while the ions remain in the urine. This process is driven by the high osmolarity of the surrounding interstitial fluid, which is maintained by the countercurrent multiplier system.

Function

The primary function of the descending limb of the loop of Henle is to reabsorb water from the filtrate, concentrating the urine. As the filtrate descends deeper into the renal medulla, the increasing osmolarity of the surrounding fluid causes more water to be reabsorbed. By the time the filtrate reaches the bottom of the loop, it is highly concentrated.

Clinical significance

Abnormalities in the function of the descending limb can lead to various kidney disorders. For example, diabetes insipidus can result from a lack of antidiuretic hormone, which normally increases the permeability of the descending limb to water. This results in an inability to concentrate urine and excessive thirst.

See also

• Loop of Henle
• Nephron
• Renal physiology