c. The Nephron. See figure 8-3 for an illustration of a nephron. Nephrons are
the functional units of the human kidney. Their primary function is to remove the wastes
of protein usage from the blood. In addition, they serve to conserve water and other
materials for continued use by the body. The end result of nephron function is a more
or less concentrated fluid called urine. The kidneys contain great numbers of nephrons,
about a million for each kidney. The main subdivisions of a nephron are the renal
corpuscle and a tubular system.
Figure 8-3. A "typical" nephron.
(1) Renal corpuscle. 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 the blood away from
the capsule. The capsule and the glomerulus together are known as the renal
corpuscle.
(2) Tubules. Each renal capsule is drained by a renal tubule. The first part of
this tubule runs quite a 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
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