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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.
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.
A flame cell is a specialized excretory cell found in simple invertebrates, including flatworms (Platyhelminthes), rotifers and nemerteans; these are the simplest animals to have a dedicated excretory system.
Normal excretion of uric acid in the urine is 270 to 360 mg per day (concentration of 270 to 360 mg/L if one litre of urine is produced per day – higher than the solubility of uric acid because it is in the form of dissolved acid urates), roughly 1% as much as the daily excretion of urea. [20]
[2] [13] [8] In both sweat gland types, the secretory coils are surrounded by contractile myoepithelial cells that function to facilitate excretion of secretory product. [ 14 ] [ 15 ] The secretory activities of the gland cells and the contractions of myoepithelial cells are controlled by both the autonomic nervous system and by the circulating ...
However, small amounts of respiration may occur, and in bats, the highly vascularized wings may account for up to 12 percent of carbon dioxide excretion. [4] In humans and most other mammals, cutaneous respiration accounts for only 1 to 2 percent. [4] [2] A lot more respiration occurs through the skin in newborn marsupials.
Urinary excretion rate = Filtration rate – Reabsorption rate + Secretion rate [1] Although the strictest sense of the word excretion with respect to the urinary system is urination itself, renal clearance is also conventionally called excretion (for example, in the set term fractional excretion of sodium).