Penington E C, Hutson J M
F. Douglas Stephens Research Laboratory, Murdoch Childrens Research Institute, Melbourne, Australia.
J Pediatr Surg. 2003 Sep;38(9):1287-95. doi: 10.1016/s0022-3468(03)00384-1.
BACKGROUND/PURPOSE: The mechanism by which the cloaca becomes partitioned into a dorsal rectal part and a ventral genitourinary sinus has been the subject of speculation for more than a century. Despite repeated suggestions that partitioning of the cloaca by fusion of lateral folds does not occur, the concept continues to hold sway in many student and surgical texts. The authors reviewed the histologic and 3-dimensional appearance of the urorectal septum in human and rat embryos to see if there was any evidence of lateral fusion in its formation.
Sprague-Dawley rat embryos (n = 143) were examined between 11 and 21 days' gestation and compared with human embryo sections (57 embryos) held in historical collections in Europe. Rat embryos were examined by microscopy, dissection, and serial histologic section. In addition, some specimens were sectioned in wax until the lumen of the cloaca was reached, after which they were dewaxed and the internal cavities imaged with scanning electronmicroscopy (n = 18 of 143).
Cloacal "partitioning" resulted from a combination of growth of the mesenchyme of the hindgut and genitourinary sinus, an alteration in the position of the cloaca in relation to surrounding structures secondary to growth in the ventral, infraumbilical abdominal wall and changes in the curvature of the developing spine, and apoptosis in the dorsal wall of the cloaca with shortening of the dorsal cloacal wall. There was no septum, as it is usually defined, between the developing bladder and hindgut. There was no evidence on either histologic section or scanning electronmicroscopy of any process of fusion occurring between the 2 lateral folds within the lumen of the cloaca.
Lateral fusion of the side walls of the cloaca does not play a role in cloacal "partition." Development of the bladder and hindgut occurs by a process that involves growth, differentiation, and remodeling.
背景/目的：泄殖腔如何分隔为背侧的直肠部分和腹侧的泌尿生殖窦，这一机制已被探讨了一个多世纪。尽管反复有人指出，泄殖腔通过侧褶融合进行分隔的说法并不成立，但这一概念在许多学生教材和外科手术教材中仍然占据主导地位。作者回顾了人类和大鼠胚胎中尿直肠隔的组织学和三维外观，以查看其形成过程中是否有侧方融合的证据。
对妊娠11至21天的斯普拉格-道利大鼠胚胎（n = 143）进行检查，并与欧洲历史收藏中的人类胚胎切片（57个胚胎）进行比较。通过显微镜检查、解剖和连续组织学切片对大鼠胚胎进行检查。此外，一些标本用石蜡包埋切片，直到到达泄殖腔管腔，然后脱蜡，并用扫描电子显微镜对内部腔隙成像（143个标本中的18个）。
泄殖腔的“分隔”是由后肠和泌尿生殖窦间充质的生长、由于腹侧脐下腹壁生长及发育中脊柱曲率变化导致泄殖腔相对于周围结构位置的改变、以及泄殖腔背壁的细胞凋亡和背侧泄殖腔壁缩短共同作用的结果。在发育中的膀胱和后肠之间不存在通常所定义的隔膜。在组织学切片或扫描电子显微镜下，均未发现泄殖腔管腔内两个侧褶之间有任何融合过程的证据。
泄殖腔侧壁的侧方融合在泄殖腔“分隔”过程中不起作用。膀胱和后肠的发育是一个涉及生长、分化和重塑的过程。
