Embryology of the hindgut
Section snippets
Theories of the normal embryology of the hindgut
Two major theories exist to explain the differentiation of the hindgut into a urogenital (ventral) and anorectal (dorsal) part: (1) septation of the cloaca; and (2) migration of the rectum.
The normal hindgut development in rat embryos
We studied the normal hindgut development by using SEM in a series of staged rat embryos between the 10th and the 15th ED. At this embryonic age rats are comparable to human embryos between the third and seventh week of gestation.4 Our studies were focused on the following:
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The development of the cloacal shape.
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Signs of fusion of lateral cloacal wall components.
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Signs of disintegration of the cloacal membrane.
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Signs of a migration of the anal opening.
Theories and recent advances studying the embryology of ARM
A number of animal models for ARM have been developed and used for embryologic studies. Depending on the nature of the model, the following observations were made:
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After feeding of 60 mg kg−1 etretinate (a long acting synthetic retinoid) to pregnant mice on ED 9, Kubota et al11 observed a specific pattern of cell proliferation and apoptosis in treated and untreated animals at ED 11 and 12. While in developmental normal embryos proliferation was noted in the area of the cloacal membrane,
The abnormal hindgut development in SD mouse embryos
The embryology of the abnormal hindgut development was unclear because of a lack of appropriate animal models that would allow systematic studies in malformed embryos. In 1940, a mouse SD mutant had been described by Dunn et al.14 These mutant-mice, first bred by Danforth15, prominently feature a short tail and are therefore also known as “Danforth's short tail mice” (Figure 6A).16 However, the SD gene influences not only the axial skeleton but also the rectum and the urogenital system, causing
Nomenclature
The term “cloaca” is used in 3 ways: It describes a transitional organ system in human embryos, a congenital anomaly, and a normal organ in birds. This nomenclature may lead to the false conclusion that the morphology of these 3 entities is similar. Embryonic cloacas are morphologically completely different from cloacas in females and in birds. The main difference is the presence/absence of the area of the future anal opening. In embryonic cloacas, the future anal region is always present,
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(1987) Sur le premiers developments due cloaque du tubercle genitale et de 1 Anus chez 1'embryon mouton s, avec quelques remarques concernant le development des glandes prostatiques
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(1888)Sur 1Origin et de 1evolution de la region ano-genitale des mammiferes
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Cited by (18)
Expertise Area 1.7: Ano-uro-rectal malformations
2024, Rare and Complex UrologyThe Importance of Screening for Additional Anomalies in Patients with Anorectal Malformations: A Retrospective Cohort Study
2023, Journal of Pediatric SurgeryCitation Excerpt :According to the Krickenbeck classification for ARM, a spectrum of malformations can be encountered ranging from relatively simple types (e.g., recto-perineal or recto-vestibular fistula) to more complex and rare types (e.g., recto-urethral fistula, cloacal anomalies or rare/regional variants such as rectal atresia) [2]. Presumably, altered spatiotemporal gene expression and multifactorial disturbances in early embryogenesis (2–4 weeks) can cause complex type ARM (e.g., recto-vesical fistula or cloacal anomaly) as well as malformations of other organ systems [3–6]. ARM can occur as an isolated anomaly (non-syndromic), but may also be part of the VACTERL-association or genetic syndromes [7–12].
Embryology and anatomy of anorectal malformations
2022, Seminars in Pediatric SurgeryCitation Excerpt :However, recent embryologic studies have not been able to confirm URS/CM fusion. Instead, the cloaca appears to remain undivided until the CM ruptures.8,10,31 Normal anorectal and genitourinary development also appears to depend on the dorsal and ventral CM,10 with apoptotic cells concentrating in the CM and the dorsal rectum from the sixth to the eighth week of embryonic development causes the CM to rupture locally allowing the URS to come into contact with it.
Correlation of anorectal malformation complexity and associated urologic abnormalities
2021, Journal of Pediatric SurgeryCitation Excerpt :Anorectal malformations (ARMs) are rare congenital anomalies that affect the developing hindgut and occur at a rate of approximately 1 in 5000 births [1]. Children born with ARMs are often found to have coexisting urologic anomalies, likely because of the intimate relationship of the developing gastrointestinal and urologic systems [2–12]. The reported incidence of urologic anomalies in patients with ARM varies considerably but is estimated to occur in as many as one half of patients in large cohorts [3,4].
Inter-rater Reliability of Sacral Ratio Measurements in Patients with Anorectal Malformations
2020, Journal of Surgical ResearchCitation Excerpt :Anorectal malformation (ARM) represents a spectrum of disease processes resulting from dysgenesis of the hindgut structures during embryological development.1,2
Development of the Gastrointestinal Tract
2020, Pediatric Gastrointestinal and Liver Disease, Sixth Edition