Short loop, long loop.

Compare a cortical nephron (short loop, little vasa recta) with a juxta-medullary nephron (long loop, vasa recta): a longer loop builds a steeper medullary gradient and more concentrated urine.

Reach 1200 mOsmol L⁻¹ urine, then show a cortical nephron alone cannot.

Vasa recta is well developed in cortical nephrons; loop of Henle lies in the cortex.

• 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.

Teaching this idea? Put the simulation on your own page or LMS with this code.