What Is Defecation?
While having food, it will move from the mouth via the esophagus to the stomach. The food will then pass through the small intestine via the large intestine to the rectum. The rectum is the end portion of the large intestine that connects it with the anus, where the stools pass out from the body. The process of defecation eliminates body waste. During defecation, the fecal matter is moved from the digestive tract to the rectum through a wave of muscle contraction in the walls of the colon called peristalsis.
The rectum will not contain feces, so do not trigger it with any local reflexes that can promote defecation. The rectum can remain empty of wastes because the structure of the lower bowel is designed in that way. The sharp angle between the sigmoid colon and rectum provides resistance for the feces to enter the rectum without nervous control.
What Is Defecation Physiology?
The defecation reflex, triggered by the intestines, can cause pressure or discomfort in the rectum. This reflex can make one feel that there is a mild tightening and release in the rectum.
The rectum and anus are lined by columnar epithelium, while in the transitional zone, squamous epithelium is present. The act of defecation is controlled by two sphincters:
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Internal Anal Sphincter - It consists of involuntarily controlled smooth muscle cells.
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External Anal Sphincter - it consists of striated muscle cells that are voluntarily controlled.
The process of defecation is initially involuntary and begins in early life. But with proper training, the child learns defecation control (to control the urge to defecate).
The defecation reflex steps are:
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The unwanted digestive material is temporarily stored in the rectal ampulla (dilated part of the rectum).
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As the fecal content increases, the stretch receptors are stimulated, which results in rectal muscle contraction and relaxation of the internal anal sphincter.
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If defecation is delayed the fecal matter hardens, leading to constipation.
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As the brain sends back the signal to defecate, the external anal sphincter relaxes and the fecal matter is expelled from the rectum to the anal canal.
What Are the Types of Defecation Reflexes?
The two main types of defecation reflex are:
Myenteric Defecation Reflex: It is responsible for increasing peristalsis (involuntary constriction and relaxation of the muscles) and propelling stool toward the rectum. This gives signals to the internal anal sphincter to relax and reduces sphincter constriction.
Parasympathetic Defecation Reflex: This is the second most common type of defecation reflex. The motions of moving stools are similar in both types of defecation reflexes. However, a person cannot control the myenteric defecation reflex as it can be controlled voluntarily in the parasympathetic defecation reflex. A myenteric defecation reflex can occur without a person's parasympathetic reflex.
The other types of defecation reflexes are:
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Gastrocolic Reflex: It is nothing but the movements in the colon triggered by the distention of the stomach at the time of eating or immediately after a meal.
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Gastroileal Reflex: In this, the distention of the stomach is triggered by the relaxation of the ileocecal sphincter soon after the meal. It speeds up peristalsis in the ileum, which is the end portion of the small intestine. This allows the contents of the ileum to get emptied into the colon quickly.
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Enterogastric Reflex: Distention and acidic chyme in the duodenum and stomach, decrease digestive protein release and reduce peristalsis.
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Duodenocolic Reflex: The duodenum is distended for a short while after eating and can trigger the mass movements of the content in the colon.
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Peritoneo-Intestinal Reflex: It involves the peritoneum and the intestines.
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Renointestinal Reflex: It involves the kidney and the intestines.
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Vesicointestinal Reflex: It involves the bladder and the intestines.
What Stimulates Defecation?
The defecation reflex pathway is triggered when:
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The colon muscles will contract to move the stool toward the rectum, known as a mass movement.
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When an adequate stool is moved to the rectum, it will cause the tissues in the rectum to stretch or distend by special stretch receptors.
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There are two main sphincters around the anal canal for defecation. They are the internal anal sphincter and the external anal sphincter.
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The internal anal sphincter cannot be controlled voluntarily, but the external anal sphincter, composed of skeletal muscles, can control it.
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The defecation reflex is occurred by the relaxation of the internal and contraction of the external anal sphincter.
Can Any Medical Conditions Affect the Defecation Reflex?
The defecation reflex can be affected by several different medical conditions. These include:
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Gastrointestinal Irritation: The nerves in the gastrointestinal tract can get irritated or disturbed by stomach bugs or other intestinal infections and can affect the normal defecation reflex.
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Neurological (Brain) Disorders: Neurological disturbances like any damage of any nerves in the nervous system can also affect the transmission of signals from the brain to the anal sphincter and conversely. This can be seen in patients with stroke (a life-threatening condition due to blockage of blood supply to the brain), multiple sclerosis (a chronic disease that affects the brain, spinal cord, and optic nerves), or Parkinson's disease (a progressive neurodegenerative disorder).
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Pelvic Floor Disorders: In rectal prolapse or rectocele, the pelvic floor muscles responsible for pooping, peeing, and sexual functions will not work correctly and affect the defecation reflex.
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Spinal Cord Injuries: An injury in a person's spinal cord can lead to paraplegic or quadriplegic, where the nerve signals will not be transmitted continuously. Therefore people with these conditions will have difficulty with the defecation reflex.
Many potential causes can impair the defecation reflex, and the treatments are different for each condition. If a person does not have a proper defecation reflex, it can make them more prone to conditions like constipation. Constipation is the condition where the stools become hardened and make it difficult to pass. Even when a person ignores the defecation reflex, it can result in constipation. Chronic constipation can also make a person experience other intestinal side effects, like an intestinal blockage from the built-up stool.
How to Manage Difficulty in Defecation Reflex?
Constipation or difficulty emptying the bowels can be effectively managed by the following non-strain bowel emptying techniques.
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Abdominal Massage: An abdominal massage is done by using the palm of one’s hand in small circles in the abdomen in a clockwise direction from the left to the right side for about 10 to 15 minutes. The healthcare worker or the nurse will train one to do this. It can reduce the intake of long-term laxative medication and help to relieve flatulence and constipation. This is not suitable for everybody, so one should do this only on the advice of a healthcare professional.
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Activity: Exercise or any movement can aid in emptying the bowels by improving bowel function. Exercising for at least 30 minutes a day can help a lot to achieve normal bowel movements.
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Diet: A balanced diet plays a more important role in achieving regular bowel movements. Eating three meals a day by including foods like fiber, fruits, and vegetables with plenty of fluids in the diet can help maintain a healthy bowel and improve fecal consistency.
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Medication: Medications like painkillers, antidepressants, and iron tablets can cause constipation. Taking too many laxatives can also cause one to have loose bowels. Consult with a healthcare professional about the laxative one is using.
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Glycerol Suppositories: Glycerol suppositories can help to begin defecation. A glycerol suppository is first moistened with water and inserted into the rectum at the pointed side. It is effective within 30 minutes after the insertion. Glycerol is a mild irritant that stimulates the bowel muscle to work and increases bowel movement frequency. One can use this only after consulting with a healthcare professional.
Conclusion:
Bowel movement is a normal physiological process that can alter within an individual. When one feels difficulty in emptying the bowels, it can lead to significant feelings of distress, increasing the tension and making bowel movements even more difficult. In case of chronic constipation or bowel issues, one should consult a healthcare professional.
