The 2 Week Diet

The anus plays an important role in controlling the elimination of solid waste through defecation. When the rectum is empty or slightly full, the internal and external anal sphincters remain closed to contain the waste material and prevent defecation.

Once the fecal matter sufficiently fills the rectum and exerts pressure on the rectal walls, rectal pressure receptors send signals to the brain. This in turn sends signals to relax the internal anal sphincter. The external anal sphincter continues to hold the stool in the rectum until the voluntary signals from the cerebral cortex allow its relaxation making possible the defecation.

Neurophysiology

Physiologically, defecation is the result of an autonomous somatic reflex, thanks to which the desire to defecate can be distinguished from the act of defecating. The so-called “activation zones” in which the initial sensory stimuli arise and produce the desire to defecate are found in the rectal musculature, as well as in the anorectal line, which is the most important activation zone.

The threshold stimuli are transmitted by the spinal sensory nerves to initiate the active phase of defecation. The distention of the rectal wall also gives rise, to some extent, to the desire to defecate through the sympathetic afferent nerves. This results in a reflex relaxation of the anal sphincters, particularly the internal sphincter and a contraction of the rectal musculature. However, desire can be voluntarily suppressed.

See also: 5 ideal foods to clean the colon

Reflection of defecation

Physiology of the anus and rectum

In adult life, defecation is no longer a reflex, but usually becomes a voluntary act once the sum of the sensory stimuli is made.

The broad theme of constipation is directly related to the sensory-motor response of the entire gastrointestinal tract and of the rectum. The “trigger zones” can be completely extra-rectal and in pathological conditions, they cause constant violent contractions that lead to rectal prolapse .

In addition, the sensory and motor dispersions before, after and during the act of defecation are complex and can be reflected throughout the nervous system. Fainting, abdominal cramps, orgasms and neurocirculatory phenomena are common clinical observations as a result of defecation disorders.

Defecation can also be completely a cortical response. The central stimulation of the vagus nerve produces the defecation reflex , a contraction of the rectum and a relaxation of the anal sphincters. In this sense, it can be observed that the segmental movements of the intestines are considered to be of myogenic origin, and the intrinsic plexuses of Meissner and Auerbach control that peristalsis, that is, the intestinal contractions.

Anal and rectal physiology

In some cases the doctor may order certain tests to know your anorectal physiology. Especially in patients with problems related to defecation, such as incontinence or constipation.

Diagnostic tests are used to measure the strength of the muscles of the anal sphincter, the nerves that innervate the muscles, the mechanics of defecation, the speed of transit through the colon or determine the existence of more serious problems such as the presence of malignant tumors. These tests include:

Anorectal manometry

Physiology of the anus and rectum

Evaluates the sensation in the anal / rectal area, the tone of the anus at rest, the voluntary contraction, the anorectal reflex and the elasticity of the rectum. This test is done using a small tube inserted into the anus.

We recommend you read: Immediate remedies for a constipation crisis

Rectal / anal ultrasound

When using an ultrasound probe inserted in the anus, a series of points are marked that become an image seen on a video monitor. The images allow doctors to inspect the integrity of the sphincter muscles. Ultrasound is also used in the rectum to measure the depth of tumor growth.

Pudendal nerve test

Physiology of the anus and rectum

The pudendal nerves run to each side of the pelvis and control bladder function, sexual function and intestinal sphincter muscles. This test verifies the electrical conduction of the pudendal nerves. It is done using special electrodes on the index finger of a special glove that is inserted to press against the nerve site.

Defecation proctogram

This is a test to see the mechanics of emptying the rectum. It is done in the radiology department. Prolapse, rectocele and similar pathologies can be easily seen.

Physiology of the anus and rectum

References:

Anorectal Physiology, Colon & Rectal.org,

Anorectal physiology laboratory, Stony Brook University Hospital,

Physiology of the anus and rectum

The 2 Week Diet

LEAVE A REPLY

Please enter your comment!
Please enter your name here