THE GENITOURINARY SYSTEM
EVERY BODY cell not only must build its substance and
obtain its energy from nutrients supplied in the food you eat; it must get rid
of wastes. And all cells deliver their waste products continuously to the
blood. In turn, the blood carries them to various centers for excretion.
Thus,
carbon dioxide and some water in the form of vapor are removed from the blood
in the lungs. Salts and additional water pour out through the skin's sweat
glands. Other wastes, including water, salt, urea, and uric acid-leave the
blood in the kidneys. Blood enters the kidneys through the renal arteries and
leaves through the renal veins and, in circulating within the two kidneys, goes
through a fabulous filtering system.
The kidneys-each about 4-1/2" long,
2-1/2" wide, 1-1/2" thick, and weighing 5 ounces-are located deep in
the abdomen at about the level of the lowest ("floating") ribs.
Essentially, they are filters containing intricate plumbing-a system of tiny
tubes called nephrons whose combined length in each kidney is about 140 miles.
To the naked eye, a single nephron would resemble a grain of sand. Under a
microscope, it has the look of a twisted worm with a huge head. The head,
called the glomerulus, is covered with a network of capillaries that carry
blood continuously into the glomerulus.
The tail is the tubule. In a healthy
kidney, as blood enters a glomerulus, a fluid is separated from it. The fluid
contains neither red, nor white blood cells nor only a trace of large protein
molecules. The fluid passes along the tubule, and about 99 percent of the
water, amino acids, proteins, glucose, and minerals needed by the body are
returned to the bloodstream. The remaining fluid, with its content of waste
materials, is eliminated from the body as urine. Every 24 hours, the kidneys
filter about 200 quarts of fluid and salts.
One or two quarts of the waste go to the bladder and
are flushed out of the body. Actually, the kidneys have a tremendous reserve
capacity; they could clean nine times more fluid than they are called upon to
do, and for this reason one healthy kidney can readily serve the body's needs.
The kidneys function to maintain the correct balance between the salts and
water of the body, to get rid of any toxic substances, and to keep the body in
correct mineral balance. For example, too much potassium in the blood could
stop the heart quite as effectively as a bullet.
