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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 .
Stylised diagram of the last part of the insect's digestive tract showing malpighian tubule (orthopteran type)The Malpighian tubule system is a type of excretory and osmoregulatory system found in some insects, myriapods, arachnids and tardigrades.
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.
Glomerular filtration rate (GFR) is the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time. [4] Central to the physiologic maintenance of GFR is the differential basal tone of the afferent (input) and efferent (output) arterioles (see diagram).
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.
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis.The collecting duct participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin (antidiuretic hormone).
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.