Rectum
Last reviewed: 23.04.2024
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The rectum is the end section of the colon. Its length is on average 15 cm, diameter from 2.5 to 7.5 cm. In the rectum, there are two sections: an ampulla and an anal (anal) channel. The ampulla of the rectum (ampula recti) is located in the cavity of the small pelvis, the anal canal (canalis analis) - in the thickness of the perineum. Behind the ampulla are the sacrum and coccyx. Ahead of the gut, men have prostate gland, bladder, seminal vesicles and ampulla of the right and left vas deferens, in women - the uterus and vagina. The anus is completed by the anal opening.
The rectum forms bends in the sagittal plane. Upper - a sacral flexure (flexura sacralis), turned with a bulge back, corresponds to the concavity of the sacrum. The lower - crotch flexure (flexura perineals), directed forward, is located in the thickness of the perineum (in front of the coccyx). Bends of the rectum in the frontal plane are unstable. The upper part of the intestine is covered by the peritoneum on all sides, the middle part is on three sides, the lower part does not have a serous cover.
In the anal canal area, thickening of the intestinal musculature forms an internal (involuntary) sphincter of the anus (m.sphincter ani internus). Directly under the skin is the external (sphincter) sphincter (m.sphincter ani extemus) formed by the striated muscle fibers. He enters into the muscles of the perineum. Both sphincters close the anus and open during defecation.
The peritoneum from the sides of the rectum forms the sacro-uterine folds. Between the lateral and lateral walls of the pelvis, there are pelvic-rectum fossae. In the subperitoneal tissue of these pits pass the ureters and branches of the hypogastric vessels, and in the pits lie the tubes and ovaries.
In front the rectum in the subperitoneal space of the cavity of the small pelvis is adjacent to the vagina. The peritoneal perineal aponeurosis in women is a loose plate that makes it easy to separate the rectum from the vagina.
The rectum is supplied by one unpaired artery - the upper rectal, which is the terminal branch of the inferior mesenteric artery, and two paired - the middle rectal (branch of the internal iliac artery) and the lower rectal (branch of the internal sexual artery). Arterial trunks have a longitudinal direction in relation to the wall of the intestine.
Venous outflow from the rectum goes to two venous systems - the lower hollow and portal veins. In this case, three venous plexuses are formed: subcutaneous, submucous and subfacial. From the upper two thirds of the rectum, venous blood flows down the upper rectal veins into the inferior mesenteric from the portal vein system, and from the lower third into the system of the inferior vena cava.
Lymph outflow from the rectum occurs in four main directions:
- from the lower parts of the rectum into the inguinal lymph nodes;
- from the upper parts to the sacral lymph nodes;
- from the anterior parts to the upper rectal lymph nodes;
- from the middle sections to the lower iliac reservoirs.
Innervation of the rectum is carried out by sympathetic and parasympathetic (motor and sensitive) fibers. Sympathetic fibers originate from the inferior mesenteric, aortic plexus and reach the rectum either along the branches of the upper rectal artery or within the hypogastric nerves. The crotch of the rectum is innervated by the genital nerve, which contains motor and sensitive fibers.
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