Location | Rectum – anatomy, function and diseases

Location

The rectum lies in the small pelvis. It is located very close to the sacrum (Os sacrum), i.e. rather in the rear part of the pelvis. In women, the rectum is bordered by the uterus and the vagina.

In men, the vesicle gland (Glandula vesiculosa) and prostate (prostate gland) as well as the vas deferens (ductus deferens) and the bladder are adjacent to the rectum. The doctor also uses these positional relationships for examinations. In digital rectal examinations, for example, the prostate or uterus can be palpated with the finger via the rectum. The rectum passes through the pelvic floor. This is also where the transition from rectum to anal canal lies.

Blood Vessels

The rectum is supplied with blood through three larger vessels. The first vessel is the arteria rectalis superior. This upper rectal artery supplies the largest part of the rectum as well as the corpus cavernosum recti.

This corpus cavernosum recti is an erectile tissue. The corpus cavernosum is filled with blood. During the continence phase or the filling phase of the rectum, the contraction of the two sphincters causes the venous outflow of the erectile tissue to be squeezed.

This allows the corpus cavernosum to fill with blood but not to empty. This ensures an additional gas-tight seal. The second vessel supplying the rectum is the arteria recatlis media.

It mainly supplies the lower part of the ampoule. The third vessel is the arteria rectalis inferior. It supplies the anal canal and the sphincter muscles.

Function

In order to ensure a secure closure of the rectum and thus the holding of the stool, the rectum and the anal canal are equipped with a complex muscle system. This muscle system is also called sphincter system (sphincter muscle). The sphincter system consists of three different muscles.

The inner sphincter (Musculus sphincter ani internus) is a reinforcement of the ring muscle of the rectum. It belongs to the smooth muscle system and therefore cannot be controlled arbitrarily. The inner sphincter muscle is under permanent tension.

This muscle slackens only to empty the bowel.The external sphincter muscle (Musculus spincter ani externus) pinches the anal canal from both sides. This causes the external sphincter muscle to shape the anal canal into a narrow slit. The external sphincter muscle is also under constant tension and thus closes the anal canal.

In contrast to the inner sphincter, however, the outer sphincter is a striated muscle and can therefore be controlled arbitrarily. The last muscle that belongs to the sphincter system is the Musculus puborectalis. This muscle is also striated.

The muscle puborectalis surrounds the rectum like a loop. This further increases the curvature formed by the flexura perinealis. This also contributes to the closure of the rectum.

The Musculus puborectalis constricts the lumen of the rectum to a slit, which is cross-shaped to the other constriction of the outer sphincter muscle. The fact that stool can be held in the rectum is called continence. Continence is ensured by several structures involved.

The sphincter system closes the rectum and the anal canal from two sides in a crossed fashion. In addition, the corpus cavernosum recti fills up with blood in the event of back pressure and thus additionally seals the intestine for any gases that may escape. The rectum contains stretch and touch receptors.

When the rectum fills with stool, these receptors trigger a feeling of urge to defecate. The inner sphincter muscle relaxes involuntarily via nerve connections. The external sphincter and the puborectal muscle also relax.

This can cause the anal canal to dilate, since the intestinal lumen is no longer closed. The corpus cavernosum is also emptied by the decreasing muscle tension. By contractions of the longitudinal muscles of the rectum the stool can now be expelled additionally. This can be further intensified by increasing the pressure in the body using the abdominal press, resulting in defecation.