View source for Cloaca (embryology)

{{Infobox Embryology |
  Name          = {{PAGENAME}} |
  Latin         = |
  GraySubject   = 241 |
  GrayPage      = 1109 |
  Image         = Gray1116.png |
  Caption       = 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. |
  Image2        = |
  Caption2      = |
  System        = |
  Days          = 15 |
  CarnegieStage = |
  Precursor     = [[Intermediate mesoderm]] |
  GivesRiseTo   = [[Urogenital sinus]] |
  MeshName      = Cloaca |
  MeshNumber    = A13.223 |
  DorlandsPre   = c_40 |
  DorlandsSuf   = 12244279  |
}}
{{SI}}

==Overview==
{{otheruses|Cloaca}}

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'''.

==Additional images==
<gallery>
 Image:Gray977.png|Human embryo about fifteen days old. 
 Image:Gray983.png|Front view of two successive stages in the development of the digestive tube.
 Image:Gray991.png|Tail end of human embryo from fifteen to eighteen days old.
 Image:Gray992.png|Cloaca of human embryo from twenty-five to twenty-seven days old.
 Image:Gray1115.png|Tail end of human embryo twenty-five to twenty-nine days old. 
 Image:Gray1118.png|Primitive kidney and bladder, from a reconstruction. 
 Image:Gray1119.png|Stages in the development of the external sexual organs in the male and female. 
</gallery>

==External links==
* {{eMedicineDictionary|Cloaca}}
* {{EmbryologySwiss|ugenital/genitinterne04}}

{{Gray's}}
{{Development of urinary and reproductive systems}}


{{WH}}
{{WS}}