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Development of the anal canal muscles
A C Levi1, F Borghi, M Garavoglia
1Department of Human Anatomy and Physiology, University of Turin, Osp. S. Vito, Italy.
Insights
This study details human embryonic development of anal canal muscles. Key findings show the external anal sphincter and puborectalis muscle originate from common structures, with smooth muscle developing later.
Area of Science:
- Embryology
- Human Anatomy
- Musculoskeletal Development
Background:
- Understanding the developmental origins of pelvic floor muscles is crucial for diagnosing congenital anomalies.
- Previous research has established distinct origins for various pelvic floor muscles, but their common developmental pathways require further elucidation.
Purpose of the Study:
- To investigate the embryologic development of the human anal canal musculature.
- To clarify the common origins of the external anal sphincter, puborectalis muscle, and levator ani complex.
- To determine the developmental timing of striated versus smooth muscle formation in the anal canal.
Main Methods:
- Examination of 18 human embryos.
- Histological analysis to identify muscle origins and differentiation.
- Comparative embryologic tracing of muscle primordia.
Main Results:
- The external anal sphincter originates commonly with the urogenital sphincter from the cloacal sphincter.
- The puborectalis muscle is confirmed as a component of the levator ani, sharing a common primordium with the ileococcygeus and pubococcygeus muscles.
- Striated anal musculature appears earlier in development than the smooth anal musculature.
Conclusions:
- This embryologic study provides definitive evidence for the shared developmental origins of key anal canal and pelvic floor muscles.
- The findings contribute to a refined understanding of normal anorectal morphogenesis and may inform the study of related congenital disorders.
Abstract:
The anal canal muscles development is studied in 18 human embryos. The external anal sphincter results to origin common with the urogenital sphincter from the cloacal sphincter. The muscle, after its appearance, is subdivided into two portions from a thin mesenchymal layer. Moreover, our embryologic study clearly confirms that the puborectalis muscle is a portion of the levator ani, its primordium being common with the ileo and the pubococcygeus muscles. The anal smooth musculature appears later than the striated one.