Cloacal membrane

Cloacal membrane
Tail end of human embryo from fifteen to eighteen days old.
Details
Latin	membrana cloacalis
Carnegie stage	7
Days	15
Precursor	caudal end of the primitive streak
Identifiers
Code	TE E5.4.0.0.0.0.15
Anatomical terminology

The cloacal membrane is the membrane that covers the development of the urinary and reproductive organs.

It is formed by ectoderm and endoderm coming into contact with each other.^[1] As the human embryo grows and caudal folding continues, the urorectal septum divides the cloaca into a ventral urogenital sinus and dorsal anorectal canal. Before the urorectal septum has an opportunity to fuse with the cloacal membrane, the membrane ruptures, exposing the urogenital sinus and dorsal anorectal canal to the exterior. Later on, an ectodermal plug, the anal membrane, forms to create the lower third of the rectum.

References

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

^ "Endoderm -- Developmental Biology -- NCBI Bookshelf".

External links

Swiss embryology (from UL, UB, and UF) hdisqueembry/triderm04
genital-021—Embryo Images at University of North Carolina
Diagram at unsw.edu.au
Overview at ana.ed.ac.uk

Development of the urinary and reproductive systems

Common

Mesoderm
- Intermediate mesoderm
- Lateral plate mesoderm ("LPM")

Endoderm → Cloaca → US

Endoderm+Ectoderm → Cloacal membrane

Urinary system

Nephrogenic cord → Kidney

Nephrotome → Pronephros

Mesonephros (Mesonephric tubules)

Mesonephric duct → Ureteric bud + Metanephrogenic blastema

US → Urinary bladder + Urethra + Primary urethral groove + Urachus

Reproductive system

Internal	Gonadal ridge → Indifferent gonad → Sex cords (Cortical cords, Testis cords) Pronephric duct → Mesonephric (Wolffian) duct + Paramesonephric (Müllerian) duct (Vaginal plate) Urogenital sinus → Prostate or Skene's gland

External	LPM Genital tubercle → Labioscrotal swelling → Scrotum or Labia majora LPM → Genital tubercle → Primordial phallus → Penis or Clitoris IM → Gubernaculum Peritoneum → Processus vaginalis or Canal of Nuck

Categories

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Cloacal membrane