Paper - The staged sequential development of the anus and rectum in human embryos and fetuses

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de Vries PA. and Friedland GW. The staged sequential development of the anus and rectum in human embryos and fetuses. (1974) J. Pediatr. Surg., 9(5): 755-69 PMID 4424274

The Staged Sequential Development of the Anus and Rectum in Human Embryos and Fetuses

By Pieter A. de Vries and Gerald W. Friedland


Summary

Human embryos do not normally have an “external cloaca”; they have at the most, a slight anal depression, but no proctodeum. The division of the cloaca into the anus and urogenital sinus is a process which involves spatially continuous mesoblastic and endodermal proliferations of the cloacal wall. This results in the establishment of a horseshoe-shaped septum, which constricts onto the cloacal membrane because of cellular growth.


The cloacal folds represent the heaped-up mesoblast around the cloacal orifice. Within the folds at the locus of the urorectal septum in front of the anus, the mesoblast is an inseparable part of the septal structure. In contradistinction, the separated anal tubercles fuse medially to separate the cloaca from the tailgut. These folds do not, however, contribute to the formation of an “external cloaca.” The apparent cephalocaudal and dorsoventral growth is explicable within the recognized parameters of axial cell migrations and proliferations.


Carnegie Embryos

The following Carnegie Embryos were used in this study.

2053

5072

6344

6432

7650

9222

9251


Cite this page: Hill, M.A. (2019, September 19) Embryology Paper - The staged sequential development of the anus and rectum in human embryos and fetuses. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_The_staged_sequential_development_of_the_anus_and_rectum_in_human_embryos_and_fetuses

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G