Development
- Development: The hindgut forms the distal colon, rectum, and upper anal canal. The cloaca is divided by the urorectal septum into the anorectal canal and urogenital sinus. This relationship is an important landmark for clinical anatomy.
- The cloaca is an early shared chamber for urinary and intestinal outlets, and the urorectal septum divides it into posterior anorectal and anterior urogenital portions.
- Development: The lower anal canal develops from ectodermal proctodeum. Failure of normal separation or canalization can produce anorectal malformations. The developmental relationship explains important adult anatomic connections.
- The proctodeum is the embryonic surface depression that forms the lower anal canal, and canalization means forming or opening a hollow passage.
- Development: The indifferent gonad develops from genital ridges. Primordial germ cells migrate to the ridges. The developmental relationship explains important adult anatomic connections.
- Development: In males, Sertoli-cell anti-Mullerian hormone suppresses Mullerian ducts, and Leydig-cell testosterone supports Wolffian duct development. The external genitalia masculinize under dihydrotestosterone. The developmental relationship explains important adult anatomic connections.
- Development: In females, absence of anti-Mullerian hormone permits Mullerian-duct development into uterine tubes, uterus, and upper vagina. Absence of testosterone permits Wolffian-duct regression and female external development. The developmental relationship explains important adult anatomic connections.
- The indifferent gonad can develop toward testis or ovary; Mullerian ducts form many internal female tract structures, Wolffian ducts form many internal male duct structures, and DHT helps masculinize external genitalia.
- Development: The ovaries descend to the pelvis. The testes descend through the inguinal canal into the scrotum, guided by the gubernaculum. The processus vaginalis accompanies them and normally obliterates. This relationship is an important landmark for clinical anatomy.
- The gubernaculum is a fibrous guide for gonadal descent, and obliteration means the processus vaginalis normally closes so it no longer leaves an open peritoneal connection.
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