Cloaca
Cloaca
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Cloaca

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Cloaca

A cloaca (/klˈkə/ kloh-AY-kə), pl.: cloacae (/klˈsi/ kloh-AY-see or /klˈki/ kloh-AY-kee), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilaginous fish and a few mammals (monotremes, afrosoricids, and marsupial moles) have this orifice, from which they excrete both urine and feces; this is in contrast to most placental mammals, which have separate orifices for evacuation and reproduction. Excretory openings with analogous purpose in some invertebrates are also sometimes called cloacae. Mating through the cloaca is called cloacal copulation and cloacal kissing.

The cloacal region is also often associated with a secretory organ, the cloacal gland, which has been implicated in the scent-marking behavior of some reptiles, marsupials, amphibians, and monotremes.

The word is from the Latin verb cluo, "(I) cleanse", thus the noun cloaca, "sewer, drain".

Birds reproduce using their cloaca; this occurs during a cloacal kiss in most birds. Birds that mate using this method touch their cloacae together, in some species for only a few seconds, sufficient time for sperm to be transferred from the male to the female. For palaeognaths and waterfowl, the males do not use the cloaca for reproduction, but have a phallus.

One study has looked into birds that use their cloaca for cooling.

Among falconers, the word vent is also a verb meaning "to defecate".

Among fish, a true cloaca is present only in elasmobranchs (sharks and rays) and lobe-finned fishes. In lampreys and in some ray-finned fishes, part of the cloaca remains in the adult to receive the urinary and reproductive ducts, although the anus always opens separately. In chimaeras and most teleosts, however, all three openings are entirely separated.

With a few exceptions noted below, mammals have no cloaca. Even in the marsupials that have one, the cloaca is partially subdivided into separate regions for the anus and urethra.

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