Figure 4-2. The nephron unit.
(a) Structure. The renal corpuscle has a hollow double- walled sac
called the renal capsule (Bowman's capsule). Leading into the capsule in a very small
artery called the afferent arteriole. Within the capsule, this artery becomes a mass of
capillaries known as the glomerulus. An efferent arteriole drains blood away from the
capsule. The capsule and glomerulus together are known as the renal corpuscle.
(b) Function. An afferent arteriole supplies blood to the glomerulus.
An efferent arteriole drains blood from the glomerulus. The blood from the afferent
arteriole fills the glomerulus. Because of a pressure gradient, a large percentage of
fluid in this blood passes through the wall of the glomerular capillary. The fluid then
passes through the inner wall of the capsule. This brings the fluid into the hollow space
between the inner and outer walls of the renal capsule.