The submucous coat of the rectum is sufficiently lax to permit considerable sliding of the mucous membrane on the muscular coat. Blood vessels ramify within it, and perpendicular processes are given off which perforate both internal and external muscular layers and blend with surrounding fatty tissue. The mucous membrane corresponds in general characters with that of other parts of the bowel but is modified for its location and function. It forms folds known as columns of Morgagni at its point of union with the skin of the anus, containing bands of longitudinal muscle fibres. These vertical folds diminish when the bowel is distended but do not entirely disappear.
<Callout type="important" title="Key Anatomy">Understanding the arrangement and distribution of muscular fibers in the rectum is crucial for diagnosing and treating diseases affecting this area.</Callout> The mucous membrane may be divided into three layers: muscular, glandular, and epithelial. The muscular layer consists of unstriped muscle tissue about 0.02 mm thick, found everywhere in the deepest layer of the mucous membrane from the esophagus to the rectum but more strongly developed near the anus. It serves to hold the membrane in place and prevent prolapse.
The glandular layer is approximately 0.07 mm thick and consists of Lieberkuhn’s follicles, tubular depressions arranged with great regularity. These follicles are lined with epithelial cells that form a network similar to a honeycomb structure. The intertubular tissue forms a fine trabecular network.
The muscles of the rectum and anus include the external and internal sphincters, levator ani, ischio-coccygeus, retractor recti or recto-coccygeus, and transversus perineii. The external sphincter muscle is a thin subcutaneous layer surrounding the anus in an elliptical form, divided into superficial and deep portions. It closes the anus and antagonizes proper dilators of the anus as well as peristaltic action.
The internal sphincter is an involuntary muscle situated immediately above and partly within the deeper portion of the external sphincter, separated by a layer of fatty connective tissue. Its thickness ranges from two lines to one inch vertically, growing thicker and stronger as it approaches the anus.
Key Takeaways
- The submucous coat allows for sliding of mucous membrane on muscular coat, facilitating blood vessel ramification and tissue binding.
- Mucous membrane forms folds called columns of Morgagni at the junction with anal skin, containing longitudinal muscle fibres.
- Muscular layer holds the mucous membrane in place to prevent prolapse.
Practical Tips
- Understanding the anatomy helps in identifying abnormalities during rectal examinations.
- Recognizing the muscular layers can aid in diagnosing conditions like internal sphincter weakness leading to a patulous anus.
Warnings & Risks
- Misinterpretation of anatomical features such as sacculi may lead to unnecessary medical interventions.
- Weakness or damage to the external sphincter muscle can cause significant issues with bowel control and hygiene.
Modern Application
While this chapter provides detailed historical insights into rectal anatomy, modern imaging techniques like MRI and CT scans offer clearer visualizations. However, understanding traditional anatomical descriptions remains crucial for accurate diagnosis and treatment planning.
Frequently Asked Questions
Q: What are the columns of Morgagni?
The columns of Morgagni are vertical folds in the mucous membrane at its point of union with the skin of the anus. They contain bands of longitudinal muscle fibres and diminish when the bowel is distended but do not entirely disappear.
Q: What is the function of the muscular layer of the rectum's mucous membrane?
The muscular layer, about 0.02 mm thick, serves to hold the mucous membrane in place and prevent prolapse by being more strongly developed near the anus.
Q: How does the internal sphincter differ from the external sphincter?
The internal sphincter is an involuntary muscle situated immediately above and partly within the deeper portion of the external sphincter, separated by a layer of fatty connective tissue. It grows thicker and stronger as it approaches the anus.