Excretion

Excretion is a biological process that involves the removal of the waste products of metabolic processes, toxins, and excess substances from the body of an organism. The process is vital in maintaining homeostasis within the organism and preventing damage to the body.

Bee anatomy excretion glands

Process

Excretion involves the separation and elimination of substances from body fluids and tissues, usually in a specialized structure such as the kidney in mammals. This is an essential process in all forms of life. For instance, in humans and other mammals, the kidneys filter out waste products, along with excess water and electrolytes, from the blood, forming urine that is excreted from the body.

Organs Involved

• In humans and many other animals, the following organs are involved in excretion:
• Kidneys: Remove waste products from the blood through the formation of urine.
• Lungs: Expel carbon dioxide, a waste product of respiration.
• Skin: Sweat glands in the skin excrete sweat which contains water, salts, and small amounts of urea.
• Liver: Detoxifies harmful substances and produces urea as a waste product.
• Large Intestine: Expels solid waste and some water, salts, and indigestible substances.

Importance

Excretion is a crucial physiological process that allows organisms to maintain their internal environment, a process known as homeostasis. By removing waste products and toxins, excretion helps to prevent their accumulation and potential harmful effects.

Mammalian excretion

• In mammals, excretion is the formation of urine in the kidneys, and expelling carbon dioxide from the lungs. These waste products are eliminated by urination and breathing out respectively. If excretion does not occur in an organism, waste products accumulate, which eventually kill the organism.
• Also, food waste is expelled through the anus. Other substances are secreted into the bile, and then eliminated in the faeces. The skin and lungs also have excretory functions: the skin eliminates metabolic wastes like urea and lactic acid through sweating,^p395 and the lungs expel carbon dioxide.

Some terms

• Mucociliary excretion is the excretion of mucus in the respiratory system. Cilia work to clear the small passages, and coughing removes phlegm.
• Biliary excretion goes through the bile duct to the duodenum and removed in the faeces.
• Perspiration is the excretion of salts and water from the body, although the main purpose is to cool the body.

Other vertebrates

• Aquatic animals usually excrete ammonia directly into the water, as this compound is soluble and there is ample water available for dilution. In terrestrial animals ammonia-like compounds are converted into other nitrogenous materials as there is less water in the environment, and ammonia itself is toxic.
• Reptiles and birds excrete their nitrogenous wastes as uric acid in the form of a white paste. This allows efficient water retention and it can be stored more easily in the egg. Both uric acid and faeces are expelled through a common opening called the cloaca. Their waste is usually two-coloured: part white (uric acid) and part green or black (organic waste).
• Many bird species, especially seabirds, can also excrete salt via specialized nasal salt glands, the saline solution leaving through nostrils in the beak.

See Also

• Kidney
• Liver
• Lungs
• Large Intestine
• Homeostasis

References

• Sherwood, Lauralee (2011). Human Physiology: From Cells to Systems. Cengage Learning. ISBN 978-1-111-57743-7.
• Marieb, Elaine; Hoehn, Katja (2007). Human Anatomy & Physiology. Pearson Benjamin Cummings. ISBN 978-0-8053-5909-1.
• Vander, Arthur; Sherman, James; Luciano, Dorothy (2001). Human Physiology: The Mechanisms of Body Function. McGraw-Hill. ISBN 978-0-07-232169-2.

External Links

Excretion - Britannica Excretory System - National Geographic Urinary System: Facts, Functions & Diseases - Live Science

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