Cloaca (embryology)

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Cloaca (embryology)
Tail end of human embryo thirty-two to thirty-three days old. Cloaca is visible at center left. The entodermal cloaca is labeled with green, while the ectodermal cloaca is seen as a colorless creast on the outside.
Gray's subject #241 1109
Days 15
Precursor Intermediate mesoderm
Gives rise to Urogenital sinus
MeSH Cloaca
Dorlands/Elsevier c_40/12244279

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The cloaca is a structure in the development of the urinary and reproductive organs.

The hind-gut is at first prolonged backward into the body-stalk as the tube of the allantois; but, with the growth and flexure of the tail-end of the embryo, the body-stalk, with its contained allantoic tube, is carried forward to the ventral aspect of the body, and consequently a bend is formed at the junction of the hind-gut and allantois.

This bend becomes dilated into a pouch, which constitutes the entodermal cloaca; into its dorsal part the hind-gut opens, and from its ventral part the allantois passes forward.

At a later stage the Wolffian duct and Müllerian duct open into its ventral portion.

The cloaca is, for a time, shut off from the anterior by a membrane, the cloacal membrane, formed by the apposition of the ectoderm and entoderm, and reaching, at first, as far forward as the future umbilicus.

Behind the umbilicus, however, the mesoderm subsequently extends to form the lower part of the abdominal wall and symphysis pubis.

By the growth of the surrounding tissues the cloacal membrane comes to lie at the bottom of a depression, which is lined by ectoderm and named the ectodermal cloaca.

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This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.