Loop of Henle

Overview
In the kidney, the loop of henle is the portion of the nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. The loop has a hairpin bend in the renal medulla. The main function of this structure is to reabsorb water and ions from the urine. To do this, it uses a countercurrent multiplier mechanism in the medulla. It is named after its discoverer, F. G. J. Henle.

Components
It can be divided into four parts:

Blood supply
The loop of Henle is supplied by blood in a series of straight capillaries descending from the cortical efferent arterioles. These capillaries (called the vasa recta; recta is from the Latin for "straight") also have a countercurrent exchange mechanism that prevents washout of solutes from the medulla, thereby maintaining the medullary concentration. As water is osmotically driven from the descending limb into the interstitium, it readily enters the vasa recta. The low bloodflow through the vasa recta allows time for osmotic equilibration, and can be altered by changing the resistance of the vessels' efferent arterioles.

Also, the vasa recta still has the large proteins and ions which were not filtered through the glomerulus, which provides an oncotic pressure for ions to enter the vasa recta from the interstitium.