Defecation Reflex

Medically reviewed by Michele Cho-Dorado, MD on January 8, 2018Written by Rachel Nall, RN, BSN, CCRN on January 8, 2018

What is the defecation reflex?

Whether a person calls it defecation, passing stool, or pooping, going to the bathroom is an important function that helps the body rid itself of waste products.

The process of eliminating stool from the body requires the work of the defecation reflex. However, there are some situations where the defecation reflex does not work as it’s intended to. You may need treatment to ensure this reflex can work as it once did.

How does the defecation reflex work?

When you eat, food moves from the mouth to the esophagus to the stomach. The food then passes through the small intestine to the large intestine to the rectum. The rectum is the final portion of the large intestine that connects to the anus, or the opening where the body releases stool.

The defecation reflex is triggered when:

  1. The muscles in the colon contract to move stool toward the rectum. This is known as a “mass movement.”
  2. When enough stool moves to the rectum, the amount of stool causes the tissues in the rectum to stretch or distend. Inside these tissues are special “stretch” receptors designed to signal the brain when they are stretched.
  3. The defecation reflex triggers the two main sphincters around the anal canal. The first is the internal anal sphincter, which is a muscle that can’t be controlled voluntarily. The second is the external anal sphincter, which is skeletal muscle that you have some control over.
  4. The defecation reflex occurs when the internal anal sphincter relaxes and the external anal sphincter contracts. The rectoanal inhibitory reflex (RAIR) is an involuntary internal anal sphincter relaxation in response to rectal distention.
  5. After the defecation reflex is triggered, you can either delay or defecate. Delay occurs when a person doesn’t go to the bathroom immediately. There are muscles in the anal sphincter that cause the stool to move backward slightly. This effect reduces the urge to defecate. If you choose to defecate, your brain activates voluntary and involuntary muscles to move stool forward and out of your body.

There are two main defecation reflexes. The myenteric defecation reflex is responsible for increasing peristalsis and propelling stool toward the rectum. This eventually signals the internal anal sphincter to relax and reduce sphincter constriction.

The second type of defecation reflex is the parasympathetic defecation reflex. While the motions of moving stool are similar, a person can voluntarily control the parasympathetic defecation reflex, but they can’t control the myenteric one.

It’s possible that a person can have a myenteric defecation reflex without the parasympathetic reflex. When this occurs, the urge to go to the bathroom may not be as strong as when both reflexes are working.

What are the symptoms of the defecation reflex?

When the intestines trigger the defecation reflex, you may feel pressure in your rectum or even discomfort. The defecation reflex can increase pressure in the rectum by 20 to 25 centimeters of water (cm H2O), which can feel vastly different from when there is no stool in the rectum.

Sometimes, this reflex can feel like the rectum is slightly tightening and releasing.

Are there medical conditions that can affect the defecation reflex?

The defecation reflex does not always work as it should. Several different medical conditions exist that can impair the defecation reflexes. These include:

  • Gastrointestinal irritation. A stomach bug or other intestinal infection can make some nerves more irritated and others less likely to work.
  • Neurological (brain) disorders. Damage to the nervous system can affect the transmission of messages from the brain to the muscles of the anal sphincter and vice versa. Examples include when a person has had a stroke, or has multiple sclerosis or Parkinson’s disease.
  • Pelvic floor disorders. These conditions occur when the pelvic floor muscles that are responsible for pooping, peeing, and sexual functions don’t work as well as they should. Some of the conditions include rectal prolapse or rectocele.
  • Spinal cord injuries. When a person has had a spinal cord injury that causes them to be a paraplegic or quadriplegic, the nerve signals don’t always transmit normally. As a general rule, those with quadriplegia tend to have significantly more difficulty with the defecation reflex.

There are many potential causes of an impaired defecation reflex, and each has a different treatment. However, if a person doesn’t have an adequate defecation reflex, they are prone to conditions like constipation. This causes your stool to become hardened and difficult to pass. Ignoring the defecation reflex can also result in constipation. Chronic constipation increases the likelihood you will experience other intestinal side effects, such as an intestinal blockage from built-up stool.

Treatments

Whenever possible, you should take steps to make stool easy to pass. This can include drinking plenty of water and eating high-fiber foods, like fruits, vegetables, and whole grains. You also shouldn’t ignore the urge to poop when you feel it come on.

Sometimes, a doctor may recommend taking stool softeners to make stool easier to pass.

Another treatment is biofeedback. Also known as neuromuscular training, this involves using special sensors that measure pressure in the rectum and signal when the pressure is enough for a person to use the bathroom. Having these pressure sensors available can help a person identify the signs that they should be going to the bathroom.

The takeaway

If you’re having a hard time sensing when you need to go to the bathroom or are chronically constipated (you have stool that is hard to pass and/or you only pass stool every three days or more), you should see your doctor. If you are ultimately diagnosed with a defecation disorder, your doctor will help to address any underlying disease if present. Dietary and physical activity changes as well as medications or biofeedback can also help.

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