title: Normal development of hindgut and anorectum in human embryo.
abstract: OBJECTIVE
  The aim of the present analysis is to examine the morphological changes, the spatiotemporal distribution of apoptosis/proliferation in the human embryonic anorectum, to reveal the normal development of human anorectum, and investigate the possible roles of apoptosis/proliferation during anorectal development.
  
  
  METHODS
  The embryos were sectioned serially and sagittally, stained with hematoxylin and eosin (H & E) between the third and eighth week of gestation, TdT-mediated dUTP-digoxigenin nick end-labeling (TUNEL) and proliferative cell-specific nuclear antigen (PCNA) immunohistochemical staining from the sixth to the eighth week.
  
  
  RESULTS
  From the fourth to the seventh week, with the growth of the mesenchyme around the cloaca, the cloaca was remolded, subsequently, the cloacal membrane (CM) moved perpendicularly then horizontally. The dorsal cloaca gradually descended to the tail groove, the urorectal septum (URS) and the CM approximated; however, the fusion of URS with the dorsal CM was never observed. During the eighth week, the URS shifted ventrally and finally fused with the ventral CM. Moreover, from the sixth to the eighth week, the apoptotic cells were concentrated in the CM, the mesenchyme of terminal rectum, and the dorsal rectum. Meanwhile, the proliferative cells could be observed in the ventral mesenchyme around the cloaca, the CM, the fused tissue between the URS, and the ventral CM.
  
  
  CONCLUSIONS
  During the development of human anorectum, it was intriguing to reveal that the URS never fused with the dorsal CM before dorsal CM disintegration, the normal anorectal development may depend on the dorsal cloaca and the dorsal CM; furthermore, the distribution of apoptosis and proliferation in the anorectum and ventral cloacal mesenchyme played a pivotal role in the formation of the anorectum.
authors.affiliation: Department of Pediatric Surgery, Shengjing Hospital, China Medical University, No. 36 Sanhao Street, Heping District, Shenyang 110004, People's Republic of China.
authors.forename: Tao
authors.initials: T
authors.lastname: Zhang
authors.forename: Hai Lan
authors.initials: HL
authors.lastname: Zhang
authors.forename: Da Jia
authors.initials: da J
authors.lastname: Wang
authors.forename: Xiao Bing
authors.initials: XB
authors.lastname: Tang
authors.forename: Hui Min
authors.initials: HM
authors.lastname: Jia
authors.forename: Yu Zuo
authors.initials: YZ
authors.lastname: Bai
authors.forename: Zheng Wei
authors.initials: ZW
authors.lastname: Yuan
authors.forename: Wei Lin
authors.initials: WL
authors.lastname: Wang
mesh_terms: D001003:Anal Canal / Q000166:cytology / Q000196:embryology*; D017209:Apoptosis; D049109:Cell Proliferation; D004622:Embryo, Mammalian / Q000033:anatomy & histology* / Q000166:cytology / Q000196:embryology*; D006801:Humans; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D012007:Rectum / Q000166:cytology / Q000196:embryology*; D013997:Time Factors
chemical_list: D018809:Proliferating Cell Nuclear Antigen