Elimination is the process by which animals rid themselves of waste products and of the nitrogenous by-products of
metabolism. Through excretion organisms control
osmotic pressure--the balance between inorganic ions and water--and maintain
acid-
base balance. The process thus promotes
homeostasis, the constancy of the organism's internal environment.
Every organism, from the smallest
protist to the largest
mammal, must rid itself of the potentially harmful by-products of its own vital activities. This process in living things is called elimination, which may be considered to encompass all of the various mechanisms and processes by which life forms dispose of or throw off waste products, toxic substances, and dead portions of the organism. The nature of the process and of the specialized structures developed for waste disposal vary greatly with the size and complexity of the organism.
In human beings, the primary organs of elimination are the
skin, which releases
water, nitrogenous wastes and
salts, the
large intestine, which releases
water and undigested food particles, and the
kidneys which balance
pH by controlling the release of
hydronium ions, balance
salt and water levels in the blood, and dispose of
metabolic wastes like
creatinine and
urea.