The nephron

Each kidney has nearly one million nephrons, the complex tubular structures that are its functional units. Every nephron is built of two parts, a glomerulus and a renal tubule.

The glomerulus is a capillary tuft. It is formed by the afferent arteriole, a fine branch of the renal artery, and drained by the efferent arteriole.

The renal tubule starts as Bowman's capsule, a double-walled cup around the glomerulus. Glomerulus plus Bowman's capsule is the Malpighian body, or renal corpuscle.

From the capsule the tubule runs as the highly coiled proximal convoluted tubule (PCT), then the hairpin-shaped Henle's loop with a descending and an ascending limb, then the highly coiled distal convoluted tubule (DCT).

The DCTs of many nephrons open into one straight collecting duct. Many collecting ducts join and open into the renal pelvis through the medullary pyramids in the calyces.

The Malpighian corpuscle, PCT and DCT lie in the cortex; the loop of Henle dips into the medulla.

In most nephrons the loop is very short and reaches only a little way into the medulla: cortical nephrons. In some the loop is very long and runs deep into the medulla: juxta medullary nephrons.

The efferent arteriole forms a fine capillary network around the tubule, the peritubular capillaries. One minute vessel of this network runs alongside Henle's loop as a U-shaped vasa recta, which is absent or highly reduced in cortical nephrons.