How Do Humans Control Defecation?

A rigid control over defecation may have evolved due to social amenities and an evolutionary advantage. But it’s not entirely clear. There are many reasons why humans control defecation. Let’s examine the various ways they control the process. Below are some examples. Defecation reflex and anorectal manometry are two of the most common. Both of these methods are invasive and have long waiting periods.

Anal sphincter

The external anal sphincter relaxes in response to the voluntary signal to defecate. Periodic mass movements in the large intestine initiate defecation and force feces out of the rectum. The need to defecate is felt by the brain in the superior frontal gyrus and anterior cingulate gyrus, which are responsible for the experience of fullness in the rectal cavity. Fullness of the rectal cavity stimulates pressure receptors on the pelvic floor, which trigger the rectoanal inhibitory reflex and allow the internal anal sphincter to relax.

Defecation reflex

There are many causes of impaired defecation reflexes. For example, spinal cord injury can cause nerve signals to not be transmitted continuously, affecting the defecation reflex. Other causes include neurological disorders, such as Parkinson’s disease, multiple sclerosis, and stroke. In addition, some pelvic floor disorders can interfere with defecation reflexes and cause symptoms including constipation and hard stools.

Anorectal manometry

Anorectal manometry is a medical test performed to measure the function of the sphincters that control bowel movements and defecation. These muscles control the opening and closing of the anus and the rectum, which holds stool until defecation. The test is done while the patient lies on his or her side. During the procedure, a small, flexible catheter with a balloon attached is placed into the rectum. A doctor will then attach the balloon to the machine, which measures the pressure changes in the balloon.


Sigmoidoscopy is a procedure that is similar to a colonoscopy. Before the procedure, the patient must undergo an enema, which will empty the bowel. This may require a second enema the night before the procedure. The physician may also request that you change into a hospital gown. During the procedure, the doctor may also use a rigid scope to view your colon.


Defecation and defection are important aspects of human health. A defecography can show the mechanics of the pelvic floor and provide important information for determining the cause of anorectal motility problems. In a standard defecation test, the doctor will insert a barium paste into the rectum with a caulking gun. The barium paste then slowly leaves the body, allowing the physician to visualize the mechanics of the pelvic floor. Defecation and defecography are also helpful in diagnosing pelvic floor problems like leaky stool, painful bowel movements, and anal pain.

Withholding behavior

When examining the literature on withholding behavior during defecation, parents should first understand the reasons for this behavior. Some authors simply mention it as common behavior, while others describe it as a separate behavior. However, it does not appear to be limited to children with autism. Other signs of withholding behavior during defecation include wriggling, retentive posturing, and clenching the buttocks.

Nerve damage

The nerves of the anus and rectum must be functioning properly for bowel movement. They control the muscles in the rectum and signal when it is full. Damage to these nerves can impair bowel function and reduce peristalsis in the colon. It can also block the signals to the rectum and anus, preventing bowel movement. This article will explain some common causes and treatments for nerve damage during defecation.