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The dual function of excretory systems is the elimination of the waste products of metabolism and to drain the body of used up and broken down components in a liquid and gaseous state. In humans and other amniotes ( mammals , birds and reptiles ), most of these substances leave the body as urine and to some degree exhalation, mammals also expel ...
The liver and kidneys clear many substances from the blood (for example, in renal excretion), and the cleared substances are then excreted from the body in the urine and feces. [6] Aquatic animals usually excrete ammonia directly into the external environment, as this compound has high solubility and there is ample water available for dilution.
These intestinal lining cells can then either store the iron as ferritin, which is accomplished by Fe 2+ binding to apoferritin (in which case the iron will leave the body when the cell dies and is sloughed off into feces), or the cell can release it into the body via the only known iron exporter in mammals, ferroportin.
It breaks down both red and white blood cells that are spent. This is why it is sometimes known as the 'graveyard of red blood cells'. [23] A product of this digestion is the pigment bilirubin, which is sent to the liver and secreted in the bile. Another product is iron, which is used in the formation of new blood cells in the bone marrow. [5]
The feces expelled can carry diseases, most often through the contamination of food. E. coli is a particular concern. Before toilet training, human feces are most often collected into a diaper. Thereafter, in many societies people commonly defecate into a toilet.
Obstructed defecation syndrome (abbreviated as ODS, with many synonymous terms) is a major cause of functional constipation (primary constipation), [18] of which it is considered a subtype. [19] It is characterized by difficult and/or incomplete emptying of the rectum with or without an actual reduction in the number of bowel movements per week ...
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This group of amoebae is known as a cyst, which is then passed out of the person's body in the feces and can survive outside the body. If hygiene standards are poor – for example, if the person does not dispose of the feces hygienically – then it can contaminate the surroundings, such as nearby food and water.