Vasa recta (kidney)

Vasa recta are the series of straight capillaries in the medulla of the kidney. They are surrounded by the loop of Henle and are an integral part of the urine concentration mechanism in the kidney. The vasa recta, along with the loop of Henle, form the countercurrent multiplier system which helps to maintain the osmotic gradient in the medulla of the kidney.

Structure

The vasa recta are long, straight capillaries that parallel the loop of Henle in the medulla of the kidney. They originate from the efferent arterioles serving the glomeruli of the juxtamedullary nephrons, and carry blood at a slow rate to allow for osmosis and diffusion of solutes.

Function

The primary function of the vasa recta is to maintain the osmotic gradient in the medulla of the kidney. This gradient is essential for the kidney's ability to produce concentrated urine. The vasa recta achieve this by a process known as countercurrent exchange.

In countercurrent exchange, the vasa recta's blood flow is slow, allowing for maximal time for osmosis and diffusion of solutes. As the blood descends into the medulla, it loses water and gains salt, maintaining the high osmolarity of the medulla. As the blood ascends, it gains water and loses salt, again maintaining the osmotic gradient.

Clinical significance

Abnormalities in the vasa recta can lead to kidney diseases such as renal failure. In conditions such as diabetes mellitus, the high blood sugar levels can damage the vasa recta, leading to nephropathy.

See also

• Kidney
• Nephron
• Renal physiology
• Countercurrent exchange