Human Anatomy Part 1 - K. A. Dyubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2002

Special Part
Splanchnology, splanchnologia [the study of viscera] - Digestive system, systema digestorium
Intestine - Rectum - Structure of the rectum

The rectum consists of a mucous membrane (mucosa), submucosa, muscular layer, and serous coat (see Fig. 248B).

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Fig. 248. Rectum, rectum (after R. D. Sinelnikov) (Continued): B - mucous membrane, tunica mucosa

The mucous membrane, tunica mucosa, of the rectum contains glands and Solitary lymphoid nodules [follicles] and forms longitudinal folds that flatten out when the organ is distended. Above the anal canal, canalis analis, the mucosa forms 5–7 transverse folds, plicae transversae recti, which have a spiral course. Within the anal canal, there are 8–10 longitudinal folds forming the anal columns, columnae anales, which straighten out upon bowel distension. Between the anal columns lie the anal sinuses, sinus anales, which accumulate mucus to facilitate defecation. At their lower ends, the sinuses are bounded by transverse mucosal folds that form the anal Valves, valvulae anales. The columns and sinuses terminate in the middle part of the anal canal, forming a circular mucosal zone (hemorrhoidal zone), zona hemorrhoidalis, in the submucosa of which lies the hemorrhoidal venous plexus. The Veins of this plexus can become varicose in hemorrhoids, leading to bleeding (Greek *haimorrhois* – Hemorrhage).

The state of the rectal mucosa in humans can be examined on an outpatient or inpatient basis by digital rectal examination (*per rectum*) and by means of optical instruments—a colonoscope or sigmoidoscope—which is of great diagnostic significance.

The muscular layer of the mucosa is well developed within the anal columns. During the contraction of Muscle fibers, the columns shorten and the rectum widens.

The submucosa, tela submucosa, of the rectum is rich in venous and arterial networks, Lymphatic vessels, and nerve plexuses, which are extensively developed in the hemorrhoidal zone and serve as the site of hemorrhage.

The muscular coat, tunica muscularis, is formed by two layers: an inner circular layer, stratum circulare, and an outer longitudinal layer, stratum longitudinale. The circular layer is thickened in the upper part of the anal canal, forming the internal anal sphincter, m. sphincter ani internus, which consists of Cytology/cytology/32.html">Smooth Muscle tissue and acts as an involuntary sphincter. The external anal sphincter, m. sphincter ani externus, is composed of Striated muscle tissue and lies subcutaneously; it is part of the pelvic Diaphragm Muscles and Functions as a voluntary sphincter.

The serous coat, tunica serosa, covers the rectum on all sides (intraperitoneally) only in its upper part (supra-ampullary section), forming a short mesorectum. The middle part of the rectum is covered by the Peritoneum anteriorly and laterally (mesoperitoneally), while in the lower part—at the level of the IV sacral vertebra—the peritoneum covers only the anterior surface of the organ (extraperitoneally) and is reflected onto the posterior surface of the Urinary Bladder in males, and onto the Uterus in females.