(a) The major work of the urinary system is done by the nephrons. The
other parts of the urinary system are mainly passageways and storage areas. Each
nephron is made up of a renal corpuscle and a tubular system. Three important
functions are carried out by nephrons.
1 Nephrons control blood concentration and volume by removing
selected amounts of water and solutes.
2 Nephrons help regulate blood pH.
3 Nephrons remove toxic wastes from the blood.
(b) As the nephrons go about these activities, they remove many
materials from the blood, return the ones that the body requires, and eliminate the
remainder. The eliminated materials are collectively called urine. The entire volume of
blood in the body is filtered by the kidneys about 60 times a day.
f. Collecting Tubules. The distal convoluted tubules of several nephrons
empty into a collecting tubule. That is, several tubules join larger tubules of a renal
pyramid to form one tubule that opens at a renal papilla and drains into a calyx in the
renal pelvis. The final reabsorption of electrolytes, water, and glucose takes place in
these collecting tubules. Also, the final secretion of electrolytes and nonelectrolytes
takes place here.
A ureter is a tubular structure that is continuous with the renal pelvis. The
ureters, one for each kidney, are musculomembranous in structure, 10 to 12 inches
long, and form the upper part of the renal pelvis of the kidney. The ureters convey urine
from the kidneys to the bladder by the process of peristalsis. Urine moves along the
ureters drop by drop, pushed by the wave-like muscular contractions of peristalsis of the
tubular wall. From the renal pelvis, the urine drains into the ureters, entering the urinary
bladder at its base. See figure 1-6.