What Causes Constipation?

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Issue 5, Volume 111

By Angel Liu 

There comes a day when you suddenly experience extreme difficulty trying to excrete feces, to the point in which you wonder if you will excrete out your intestines instead. Well, congratulations: you have constipation.

One of the functions of the large intestine is to absorb water from the food you eat, so if waste is left inside the body for too long, it undergoes scybalation, a condition in which the feces becomes pebble-like. This problem usually resolves itself with time, but if the condition persists for several weeks or more, it becomes chronic constipation.

The cause of constipation can be summed up as stool moving too slowly through the colon. Usually, during defecation, the colon automatically contracts to push stool through itself and out of the rectum. It can perform two types of contractions: repetitive non-propulsive contractions, which suck water out of fecal matter and do not move it, and high-amplitude propagated contractions (HAPCs), which do move fecal matter. The frequency of HAPCs is lower during constipation. When HAPCs move fecal matter into the rectum, they give rise to an urge to defecate. If you are unable to defecate in a particular situation, the rectum stores the stool temporarily. To expel the stool, you need to relax the anal sphincters and puborectalis muscle, which are located in the rectal region, and contract the diaphragm, abdominal, and rectal muscles, which are muscles that contract to push out stool.

The causes of constipation can be categorized into two groups: primary causes and secondary causes. Primary causes occur when the body has internal issues, such as a malfunction of the large intestine or other muscles. Secondary causes arise from external factors, such as medications. Drugs like opiates and antidepressants can reduce smooth muscle contractions. Diseases such as cancer and Parkinson’s also play a role in secondary causes. For example, Parkinson’s disease affects muscle movement due to a lack of dopamine. This also impacts muscles like the anal sphincter and pelvic floor, which function to push out fecal matter.

The three major types of primary constipation are normal transit constipation, slow transit constipation, and defecatory disorders. Normal transit constipation is the most common type of constipation. It happens when the stool is too hard to be excreted, and there is a problem with the excretion process, causing you to defecate less frequently. However, there is no innate problem concerning stool movement and colon relaxation. It is the easiest type to treat, usually with fiber supplements or osmotic laxatives. Osmotic laxatives, as per their name, draw water into the large intestine to make the stool softer.

Slow transit constipation happens when there is a problem with colon motility. This occurs when waste takes longer than normal to pass through and HAPCs do not increase when they’re supposed to, such as after meals. You may defecate less than once per week and not necessarily feel the urge to defecate either. The causes are believed to be a loss of interstitial cells, which are cells in the reproductive system that secrete hormones, and conflict between neuron transmissions in the gut. It most commonly occurs in young women, starting in puberty, and is often accompanied by abdominal pain and bloating. The most common treatment for this disorder is laxatives.

Defecatory disorders happen when dysfunction of the pelvic floor or anal sphincter causes difficulty moving stools. It is extremely hard to defecate with this condition, and patients may even have trouble urinating. Like slow transit constipation, patients with defecatory disorders have hyposensitivity (decreased sensory input) and do not feel the urge to defecate. The most common defecatory disorder, dyssynergia, occurs due to psychological factors. A history of poor toilet usage, painful excretions, back injuries, and brain-gut disorders, as well as eating disorders and sexual and physical abuse, can contribute to dyssynergia. Laxatives do not work on people with this condition. Instead, treatments include physical therapy, nutritional therapy, and surgery, among others.

Most of us have had constipation at one point or another, with 16 percent of the U.S. population suffering from chronic constipation, a large portion of it being among the elderly. Knowing what causes constipation and how to remedy it allows you to tailor your lifestyle to be less affected by it. As a common problem, it is worth studying.