Elimination, also called excretion, is the process of removing water, waste matter, and harmful substances from the body. The skin, lungs, kidneys, and lower intestinal tract carry out this function. The kidneys eliminate most of the excess water and salt. However, an average of about 1 quart (0.95 liter) of water and 1/3 teaspoonful (1.6 milliliters) of salt are eliminated through the skin every day. When visible sweating occurs, the elimination of water and salt by the skin may be much greater. Perspiration withdraws from the body about one-fourth of all the heat produced.
The process of respiration eliminates carbon dioxide and some water. An adult eliminates about 64/5 ounces (200 milliliters) of carbon dioxide each minute.
Many different substances pass out of the body through the kidneys. They eliminate daily about 11/2 quarts (1.4 liters) of urine, consisting of water and certain solids. Urine contains the solid urea, a waste product of the use of protein by the body. Another solid is salt, or sodium chloride. Elimination of certain acid salts, such as acid sodium phosphate, also takes place. Excess sodium bicarbonate (baking soda) is sometimes eliminated in the urine by the kidneys. The body rids itself of waste products of digestion through the large intestine.
