open into a straight tube called collecting duct. The collecting duct runs through the medullary pyramids in the region of the pelvis. Several collecting ducts fuse to form papillary duct that delivers urine into the calyces, which opens into the renal pelvis. In the renal tubules, PCT and DCT of the nephron are situated in the cortical region of the kidney whereas the loop of Henle is in the medullary region.
In majority of nephrons, the loop of Henle is too short and extends only very little into the medulla and are called cortical nephrons. Some nephrons have very long loop of Henle that run deep into the medulla and are called juxta medullary nephrons (JMN) (Figure . a and b) XI Std Biology-Zoology Chapter- arteriole that comes out of the glomerulus forms a fine capillary network around the renal tubule called the peritubular capillaries. The efferent arteriole serving the juxta medullary nephron forms bundles of long straight vessel called vasa recta and runs parallel to the loop of Henle.
Vasa recta is absent or reduced in cortical nephrons (Figure . ). What is the importance of having a long loop of Henle and short loop of Henle in a nephron?