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Excretion is elimination of metabolic waste, which is an essential process in all organisms. In vertebrates , this is primarily carried out by the lungs , kidneys , and skin . [ 1 ] This is in contrast with secretion , where the substance may have specific tasks after leaving the cell .
The excretion of urea is called ureotelism. Land animals, mainly amphibians and mammals, convert ammonia into urea, a process which occurs in the liver and kidney. These animals are called ureotelic. [3] Urea is a less toxic compound than ammonia; two nitrogen atoms are eliminated through it and less water is needed for its excretion.
Only the organs specifically used for the excretion are considered a part of the excretory system. In the narrow sense, the term refers to the urinary system. However, as excretion involves several functions that are only superficially related, it is not usually used in more formal classifications of anatomy or function.
This is an accepted version of this page This is the latest accepted revision, reviewed on 13 November 2024. This article is about the human urinary system. For urinary systems of other vertebrates, see Urinary systems of birds, urinary systems of reptiles, and urinary systems of amphibians. Anatomical system consisting of the kidneys, ureters, urinary bladder, and the urethra Urinary system 1 ...
Egestion (Excretion): Removal of undigested materials from the digestive tract through defecation. Underlying the process is muscle movement throughout the system through swallowing and peristalsis. Each step in digestion requires energy, and thus imposes an "overhead charge" on the energy made available from absorbed substances.
The urea cycle converts highly toxic ammonia to urea for excretion. [1] This cycle was the first metabolic cycle to be discovered by Hans Krebs and Kurt Henseleit in 1932, [2] [3] [4] five years before the discovery of the TCA cycle. The urea cycle was described in more detail later on by Ratner and Cohen.
In physiology, respiration is the transport of oxygen from the outside environment to the cells within tissues, and the removal of carbon dioxide in the opposite direction to the environment by a respiratory system.
Human waste (or human excreta) refers to the waste products of the human digestive system, menses, and human metabolism including urine and feces.As part of a sanitation system that is in place, human waste is collected, transported, treated and disposed of or reused by one method or another, depending on the type of toilet being used, ability by the users to pay for services and other factors.