Excretion is a part of metabolism, carried out by removal of final and intermediate products of metabolism and excessive alien materials from organism into the environment, to ensure the optimum composition of the internal environment and the normal functioning of the body. Excretion processes are an integral feature of life, so their violation leads inevitably to violations of homeostasis, metabolism and body functions, until its death. The primary organs of excretion are the kidneys, that form and release urine together with the substance to be excreted from the body. Kidneys are also the main organ that ensures water-salt metabolism in human organism, regulating acid-base balance.
Also, the end-products of metabolism are excreted from the body by human lungs (carbon dioxide, volatile compounds, water vapor), skin and intestine (undigested food residues). Thus, the lungs excrete carbon dioxide, water vapor, some volatile substances such as ether vapor, chloroform after anesthesia, and pair of alcohol intoxication from the body. Sweat glands excrete salt and water, small amounts of urea, uric acid, and lactic acid while intense muscular work. Salivary and gastric glands excrete certain heavy metals, a number of drugs, alien organic compounds. Important excretory function is performed by liver, removing the blood hormones, cleavage products of hemoglobin, nitrogen metabolism and many other substances from blood. Pancreas and intestinal glands excrete heavy metals, drugs.
However, the main role in the excretion belongs to the specialized organs – kidneys. The most important functions of the kidneys is involved in the regulation of:
- the volume of blood and other fluids of organism,
- the constancy of the osmotic pressure of blood and other body fluids,
- the ionic composition of fluid inside the medium and the ionic balance of the body,
- acid-base balance,
- excretion of end products of nitrogen metabolism and alien substances.
Thus, the kidney is the organ that ensures homeostasis of the internal environment.
The process of selection is essential for homeostasis, it provides an exemption of the body from end-products of metabolism, which can no longer be used, alien and toxic substances and excess water, salts and organic compounds, arrived with the food or formed as a result of metabolism. Excretion is performed by many organs, but the main are human kidneys, lungs, skin, and digestive tract.
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Spilsbury, L.; Spilsbury, R. (2008). Digestion and Excretion, p. 18.
Walsh, P.J.; Wright, P.A. (1995). Nitrogen metabolism and excretion. Pp. 215-216.