The cloaca is a structure in the
development of the urinary and reproductive organs
The development of the urinary system begins during prenatal development, and relates to the development of the urogenital system – both the organs of the urinary system and the sex organs of the reproductive system. The development continues a ...
.
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 endodermal 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
The mesonephric duct (also known as the Wolffian duct, archinephric duct, Leydig's duct or nephric duct) is a paired organ that forms during the embryonic development of humans and other mammals and gives rise to male reproductive organs.
Stru ...
and
Müllerian duct
Paramesonephric ducts (or Müllerian ducts) are paired ducts of the embryo that run down the lateral sides of the genital ridge and terminate at the sinus tubercle in the primitive urogenital sinus. In the female, they will develop to form the fal ...
open into its ventral portion.
The cloaca is, for a time, shut off from the anterior by the
cloacal membrane, formed by the apposition of the
ectoderm and
endoderm, 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
In anatomy, the abdominal wall represents the boundaries of the abdominal cavity. The abdominal wall is split into the anterolateral and posterior walls.
There is a common set of layers covering and forming all the walls: the deepest being the ...
and
pubic symphysis
The pubic symphysis is a secondary cartilaginous joint between the left and right superior rami of the pubis of the hip bones. It is in front of and below the urinary bladder. In males, the suspensory ligament of the penis attaches to the pubi ...
.
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.
Clinical significance
A
birth defect
A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities ca ...
can arise known as a
persistent cloaca
A persistent cloaca is a symptom of a complex anorectal congenital disorder, in which the rectum, vagina, and urinary tract meet and fuse, creating a cloaca, a single common channel.
Signs and symptoms
Cloacas appear in a wide spectrum of varia ...
where the
rectum,
vagina
In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
, and
urinary tract
The urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, c ...
fuse to create a common channel or cloaca.
A rare birth defect which leaves much of the abdominal organs exposed is known as
cloacal exstrophy
Cloacal exstrophy (EC) is a severe birth defect wherein much of the abdominal organs (the bladder and intestines) are exposed. It often causes the splitting of the bladder, genitalia, and the anus. It is sometimes called OEIS complex.
Diagnosti ...
.
Additional images
File:Gray977.png, Human embryo about fifteen days old.
File:Gray983.png, Front view of two successive stages in the development of the digestive tube.
File:Gray991.png, Tail end of human embryo from fifteen to eighteen days old.
File:Gray992.png, Cloaca of human embryo from twenty-five to twenty-seven days old.
File:Gray1115.png, Tail end of human embryo twenty-five to twenty-nine days old.
File:Gray1118.png, Primitive kidney and bladder, from a reconstruction.
File:Development of external sexual organs in the male and female Gray1119.png, Stages in the development of the external sexual organs in the male and female.
References
External links
*
Embryology of digestive system
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