The urorectal septum is an invagination of the

cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds ...

. It divides it into a dorsal part (the hindgut) and a ventral part (the

urogenital sinus The urogenital sinus is a part of the human body only present in the development of the urinary and reproductive organs. It is the ventral part of the cloaca, formed after the cloaca separates from the anal canal during the fourth to seventh we ...

). It invaginates from cranial to

caudal Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...

, formed from the endodermal cloaca, and fuses with the cloacal membrane. Malformations can cause fistulas.

Structure

The urorectal septum is an embryonic structure formed from an invagination of the

. The urorectal septum divides the cloaca into two parts: * a dorsal part, forming part of the hindgut, which forms the

rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the l ...

and the

anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...

. * a ventral part, forming the

, which forms the allantois, which becomes the

urinary bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...

. The urorectal septum becomes part of the perineal body, helping to form the

perineum The perineum in humans is the space between the anus and scrotum in the male, or between the anus and the vulva in the female. The perineum is the region of the body between the pubic symphysis (pubic arch) and the coccyx (tail bone), inclu ...

Development

The urorectal septum develops from cranial to

, and is flat in the

coronal plane The coronal plane (also known as the frontal plane) is an anatomical plane that divides the body into dorsal and ventral sections. It is perpendicular to the sagittal and transverse planes. Details The coronal plane is an example of a longit ...

. It is formed from endoderm, the same germ layer as the

. It fuses with the cloacal membrane.

Clinical significance

Urorectal septum malformation

Malformation of the urorectal septum can lead to several different types of

fistula A fistula (plural: fistulas or fistulae ; from Latin ''fistula'', "tube, pipe") in anatomy is an abnormal connection between two hollow spaces (technically, two epithelialized surfaces), such as blood vessels, intestines, or other hollow or ...

Classification

women A woman is an adult female human. Prior to adulthood, a female human is referred to as a girl (a female child or adolescent). The plural ''women'' is sometimes used in certain phrases such as "women's rights" to denote female humans regardl ...

, at least five different types of

are possible. All of these involve the fusion of the

and the end of the hindgut, causing the rectum to end in the

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 hy ...

. This may be associated with the

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...

in the normal position, posterior to the hindgut, or

bicornuate A bicornuate uterus or bicornate uterus (from the Latin ''cornū'', meaning "horn"), is a type of mullerian anomaly in the human uterus, where there is a deep indentation at the fundus (top) of the uterus. Pathophysiology A bicornuate uterus ...

. In men, at least three different types of fistula are possible. The hindgut may enter and preserve the urogenital sinus after birth. The hindgut may replace the urogenital sinus completely, in which case it may also replace the

and cause the

ureters The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional e ...

to drain into it.

Prognosis

Urorectal septum malformation is associated with a number of other

birth defects 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 ...

, including

spina bifida Spina bifida (Latin for 'split spine'; SB) is a birth defect in which there is incomplete closing of the spine and the membranes around the spinal cord during early development in pregnancy. There are three main types: spina bifida occulta, m ...

deafness Deafness has varying definitions in cultural and medical contexts. In medical contexts, the meaning of deafness is hearing loss that precludes a person from understanding spoken language, an audiological condition. In this context it is written ...

, sacral hypoplasia, atrial septal defect,

ventricular septal defect A ventricular septal defect (VSD) is a defect in the ventricular septum, the wall dividing the left and right ventricles of the heart. The extent of the opening may vary from pin size to complete absence of the ventricular septum, creating one ...

tetralogy of Fallot Tetralogy of Fallot (TOF), formerly known as Steno-Fallot tetralogy, is a congenital heart defect characterized by four specific cardiac defects. Classically, the four defects are: * pulmonary stenosis, which is narrowing of the exit from the r ...

, and limb musculoskeletal disorders. Mainly because of these associations, up to 20% of children born with urorectal septum malformation may not survive long-term. Outcomes from corrective surgery on a urorectal septum fistula are very good.

References

External links

Subdividing the cloaca

http://cancerweb.ncl.ac.uk/cgi-bin/omd?urorectal+septum

Embryology of digestive system {{developmental-biology-stub