The kidneys are the vital part of the
urinary system. Blood flowing through capillaries in renal
corpuscles carries excess water and certain other constituents.
These are filtered out and collected by a funnellike capsule, from
which the filtrate flows into the kidney tubules. Each kidney
contains over one million nephrons, one of the kidney's many
functioning units. Blood flows into the glomerulus, and some of
its fluid, with dissolved substances, is absorbed by the cells
lining into the tubules. These tubules select part of the fluid and the
of use to the body, returning these in solution to the blood in
vessels alongside the tubule.
Waste material travels on down the tubules into the kidney pelvis, and
from there through the ureter to the bladder and out of the body
through the urethra. These waste materials in solution are the
urine. Analysis of the urine usually reveals any disease of the
Diseases of the ureters and urethra are
uncommon, except when they are affected by kidney or bladder disease.
The only important urethral infection which does not concern bladder
or kidneys is caused by gonorrhea, a venereal disease with
inflammatory discharge from the urethra or vagina. One of the
common complications of neglected gonorrhea is urethra stricture, a
narrowing or contracture of the urethra, the outlet tube of the