Cloaca

: A common passageway for feces, urine and reproduction. At one point in the development of the human embryo, there is a cloaca. It is the far end of a structure called the hindgut. This structure then divides to form a rectum, a bladder, and genitalia. The presence of a cloaca is normal in many adult animals (birds, reptiles, amphibians, some fish, and even a few mammals). However, the persistence of a persistent cloaca in a person is a birth defect (a congenital malformation). Cloaca is the Latin word for drain or sewer.

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1. In early embryos, the endodermally lined chamber into which the hindgut and allantois empty. 2. In birds and monotremes, the common chamber into which open the hindgut, bladder, and genital ducts. [L. sewer]

- ectodermal c. the proctodeum of the embryo.

- endodermal c. terminal portion of the hindgut internal to the cloacal membrane of the embryo.

- persistent c. a condition in which the urorectal fold has failed to divide the c. of the embryo into rectal and urogenital portions. SYN: sinus urogenitalis, urogenital sinus (2).

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clo·aca klō-'ā-kə n, pl -acae -.kē, -.sē

1 a) the common chamber into which the intestinal, urinary, and generative canals discharge esp. in monotreme mammals, birds, reptiles, amphibians, and elasmobranch fishes

b) the terminal part of the embryonic hindgut of a mammal before it divides into rectum, bladder, and genital precursors

2) a passage in a bone leading to a cavity containing a sequestrum

clo·acal -'ā-kəl adj

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n.

the most posterior part of the embryonic hindgut. It becomes divided into the rectum and the urinogenital sinus, which receives the bladder together with the urinary and genital ducts.

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clo·a·ca (klo-aґkə) pl. cloaґcae [L. “drain”] 1. a common passage for fecal, urinary, and reproductive discharge in monotremes, birds, and lower vertebrates. See also cloacal aperture, under aperture. 2. in mammalian embryology, the terminal end of the hindgut before division into rectum, bladder, and genital primordia (see sinus urogenitalis). Failure to divide properly during development may result in persistent cloaca (q.v.). 3. in pathology, an opening in the involucrum of a necrosed bone. cloacal adj