THE GENITOURINARY SYSTEM

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.