(a) Structure. The renal corpuscle has a hollow, double-walled sac
called the renal capsule (Bowman's capsule). Leading into the capsule is 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.
AFFERENT = carry to
EFFERENT = carry away from
(a) Structure. Each renal capsule is drained by a renal tubule. This
part of the tubular system runs a long distance in a coiled formation and is called the
proximal convoluted tubule. A long loop, the renal loop of Henle extends down into the
medulla with two straight parts and a sharp bend at the bottom. As the tube returns to
the cortex layer, it once again becomes coiled and is known here as the distal
convoluted tubule. The distal convoluted tubule is the end of the nephron unit.
(b) Reabsorption. The renal tubule reabsorbs the fluid or filtrate
passing through the tubular system, of the nephron. As fluid or filtrate passes through
the renal tubule, the majority of the water, glucose, and other valuable substances are
removed from the fluid, reabsorbed in the tubule, and returned to the cardiovascular
system. Essential electrolytes such as sodium, chloride, and bicarbonate are
reabsorbed in the tubules. The hormone aldosterone controls the reabsorption of
sodium salts. Aldosterone is a hormone produced in the adrenal gland. Water and
nonelectrolytes such as glucose, amino acids, and nutrients are also absorbed by renal
(c) Secretion. The function of the renal tubule is tubular secretion.
Tubular reabsorption removes substances from the filtrate into the blood and also adds
materials to the fluid from the blood. Substances secreted by renal tubules include
potassium ions, hydrogen ions, ammonia, creatinine, and the drugs penicillin and
aminohippuric acid. There are two main effects from tubular secretions. The
substances in the secretions help rid the body of certain materials and also help control
the blood pH.