Normal Urge to Defecate
The need to have a bowel movement is first marked by an urging. This sensation compels a person to find suitable toilet facilities so that defecation can occur. There are a number of reasons why this sensation occurs including :
- Stretching of the wall of the colon as waste and water accumulates in it.
- Increased pressure within the abdomen (intra-abdominal pressure).
- Defecation reflexes which are stimulation of the bowels by nerve signals.
- Filling of the rectum with feces.
These triggers for the defecation urge is considered normal. It occurs on daily basis for most people and facilitates the process of stool evacuation. The rectum fills with stool and the external and internal anal sphincters relax allowing stool to pass out into the environment. Once all of the stool in the rectum has been passed out, the defecation urge sensation subsides completely.
Stimulation of Urge
For most people, the urging and subsequent defecation occurs at certain times of the day particularly in the early morning. This is more likely to occur in a person with good bowel training from childhood. Other factors that may trigger the defecation urge :
- Physical activity like brisk walking.
- Pressure on the abdomen.
- After a large meal.
- Certain emotions.
All of these instances are considered normal yet it does not occur on most occasions. This is due to the fact that good bowel habit evacuates the sufficient waste material and water on a regular basis and the colon and rectum are therefore not as sensitive to additional factors.
Abnormal Defecation Urge
Sometimes the urging to defecate can be considered to be abnormal. In these cases the defecation urge persists and becomes annoying or even uncomfortable, and sometimes even painful yet it does not precede a bowel movement or subside after a bowel movement. This condition is known as tenesmus. The sensation may be considered abnormal when there is an urging in the following circumstances :
- After a bowel movement.
- Inability to have a bowel movement even with sitting or straining.
- Small volume stool is passed out – feeling of incomplete evacuation.
- Tenderness, pain or itching in the rectum.
The urge in these cases is either persistent or intermittent (recurring every now and then). It is more likely to be triggered or intensified by the stimulatory factors discussed above.
Reasons for constant urging
The wall of the bowels are able to perform many functions that facilitate movement of food and waste through the gut, release enzymes for digestion and allow for nutrients to be absorbed into the bloodstream. Water is absorbed and the waste material is held in the lower parts of the bowel until it is ready to be expelled. These functions are mainly controlled by two types of signals – hormones (chemical) and nerve impulses (electrical). The bowel walls are constantly relaying signals through nerves and hormones to other parts of the gut and even other organs. It is also receiving signals from other parts of the body through the hormones and nerves. In this way its activities can be well coordinated for efficiency.
This video explains the course of food that is eaten until waste is evacuated.
The defecation urge, as previously discussed, is caused by stretching of the colon wall as waste and water accumulates. It may also be triggered by pressure on the colon wall from within the abdomen. This causes nerve impulses to be sent to the spinal cord and back which can the initiate the defecation process. These pathways are referred to as defecation reflexes. It involves the colon and rectum and there are two types of such reflexes – inhibitory myenteric and parasympathetic defecation reflexes.
There are other defecation reflexes which are linked with other parts of the gut or even other organs in the abdomen. This means that stimulation or irritation of these organs will trigger the defecation urge and eventually lead to a bowel movement. The main such reflexes involve the stomach and small intestine. To a lesser degree, other reflexes linked to the kidney, bladder and the abdominal lining known as the peritoneum may play a role in initiating defecation.
Therefore irritation or disease of these structures may lead to the urge to defecate :
- colon or rectum (most likely)
- stomach or small intestine
- kidney, bladder or peritoneum
Causes of Abnormal Urging
The most common cause of abnormal defecation urging is constipation. However, constipation on its own is a symptom and not a disease. Persistent or intermittent defecation urging is common with constipation and usually temporary. The cause of constipation in most cases is not known. Urging is more likely to arise with hemorrhoids, a common complication of constipation.
Colon and Rectum
- Inflammatory bowel disease (IBD) is chronic inflammation of the wall of the bowel. There are two types – ulcerative colitis and Crohn’s disease. Sometimes other parts of the gut, right up to the mouth, can be affected with Crohn’s disease.
- Irritable bowel syndrome (IBS) is a functional disorder of the bowels marked by episodes of diarrhea or constipation, bloating and abdominal pain or cramping. The cause of IBS is unknown.
- Infectious colitis is an infection of the colon that may be caused by bacteria, viruses, parasites or with an overgrowth of certain natural bacteria in the bowels.
- Colorectal growths, including polyps, benign tumors and cancer.
- Proctitis is inflammation of the rectum often caused by injury to the rectum or infections.
- Hemorrhoids are inflamed veins of the rectum and anus often associated with constipation, diarrhea and sitting on the toilet for excessively long periods of time. Tenesmus is more likely with thrombosed hemorrhoids.
- Other colon and rectal problems include obstipation, fecal impaction, ischemic proctocolitis, rectal prolapse, foreign body in the rectum, rectal perforation or perirectal abscess.
- Anal problems may include anal fissures, fistulas, abscess (perianal), cryptitis and cancer.
Due to the close proximity of the male and female reproductive organs, tenesmus may occur in conditions such as :
- Paraurethral gland infection
- Female urethral syndrome
- Pelvic inflammatory disease (PID) in rare cases.
Similarly with men, the reproductive organs lie in close proximity to the colon and rectum. Tenesmus may therefore occur with :
- Prostatitis, particularly where an infection leads to abscess formation.
- Prostate cancer
There are number of other causes which be widely varied in nature. Tenesmus may not always be present, and in some cases is rarely seen at all in these diseases.
- Laxative overuse
- Pelvic tumors
- Pinworms (human intestinal worms)
- AIDS enteropathy
Abnormal defecation urging (tenesmus) is a symptom of a disease and not a disease itself. Therefore the cause of tenesmus has to be diagnosed and treated. The sensation will then subside with successful treatment of the underlying cause. The two common causes, constipation and hemorrhoids, can be managed or even prevented with a few simple measures :
- Increase the intake of high fiber foods and water.
- Do not sit on the toilet for too long.
- Avoid excessive straining in order to facilitate the passing of stool.
- Never interfere with the anus and rectum even if it is itchy (read more on itchy rectum).
- Physical activity increases the food and waste movement in the bowels.
- Laxatives are helpful but should not be overused.
- Avoid foods that are likely to lead to constipation.
Article reviewed by Dr. Greg. Last updated on December 21, 2011