Function of the large intestine

To understand constipation, it helps to know how the large intestine works. As food passes through it, the large intestine absorbs water and forms the stool slurry. Muscle contractions of the colon push the stool towards the rectum. By the time the stool reaches the rectum it has become solid because most of the water has been absorbed.

The hard and dry stools of constipation are created when the large intestine absorbs too much water. This happens because the muscle contractions of the bowel are slow or sluggish, causing the stools to move through the colon too slowly.

What are the most common causes of constipation?

Among the most common causes of constipation are the following:

  • Lack of fiber in the diet
  • Lack of enough fluids
  • Lack of exercise
  • Lack of adequate intake of fatty acids
  • Lack of enough exercise
  • Changes in our life or routine, such as pregnancy, old age and travel
  • Abuse of laxatives
  • A delay in the need to defecate
  • Specific diseases such as multiple sclerosis and lupus
  • Colon and rectal problems
  • Problems with bowel function, e.g. chronic idiopathic constipation

The role of nutrition

The most common cause of constipation is a diet low in fiber, found in vegetables, fruit and whole grains, and high in fat, found in cheese, eggs and meat. People who eat plenty of high-fiber foods are less likely to experience constipation.

Fiber, both soluble and insoluble, is the part of fruits, vegetables and grains that cannot be assimilated by the body. The former dissolve easily in water and take on a soft, jelly-like texture in the intestines. The latter pass almost unchanged through the intestines. The large amount of soft fiber prevents the formation of hard and dry feces which are difficult to pass through the intestine.

Americans consume, on average, about 5-20 grams of fiber per day, less than the 20-35 grams recommended by the American Dietetic Association. Both children and adults consume too many refined and processed foods in which fiber has been removed.

A low-fiber diet also plays an important role in constipation in the elderly. They often have no interest in food, and may choose foods that are quickly cooked and low in fiber. In addition, tooth loss may force seniors to eat soft foods that are processed and low in fiber.

Fluid intake

Fluids, such as water and juice, add fluids to the bowel, making bowel movements softer and easier. People who have constipation problems should drink enough of these fluids, about eight glasses on a daily basis. Other liquids, such as coffee and soft drinks, that contain caffeine seem to cause dehydration.

Physical exercise

Lack of physical exercise can lead to constipation, although doctors don’t know exactly why. For example, constipation often occurs after an accident or during an illness, when one has to stay in bed and cannot exercise.

The Medicines

Painkillers, especially narcotics, antacids containing aluminum, anticonvulsants, antidepressants, iron supplements, diuretics and anticonvulsants for epilepsy can slow the passage of stool through the bowel.

Irritable Bowel Syndrome (IBS)

Some people with Irritable Bowel Syndrome, also known as spastic colitis, have spasms of the colon that affect defecation. They often alternate between constipation and diarrhea, and also complain of abdominal cramps, gas and bloating. Although irritable bowel syndrome can cause lifelong symptoms, it is not a life-threatening condition. It often worsens with stress but there is no specific cause or anything unusual that a doctor can see in the colon.

Changes in life or routine

During pregnancy, women may be constipated because of hormonal changes or because their heavy uterus compresses the bowel. Aging can also affect bowel motility because a slower metabolism results in less bowel activity and muscle tone. In addition, people often become constipated when traveling because their normal diet and daily routine is disrupted.

The abuse of laxatives

Myths about constipation have led to serious abuse of laxatives. This is common in the elderly, who are very anxious with the issue of daily bowel movements.
Laxatives are usually not necessary and may just be a habit. The colon, however, begins to rely on laxatives to make the stools. Over time, laxatives can cause damage to the nerve cells in the colon and interfere with the natural ability of the bowel to contribute to emptying. For the same reason, regular use of bedpans can also lead to a loss of normal bowel function.

Delaying the need for voiding

People who ignore the need to void may eventually stop this desire, which can lead to constipation. Some people delay voiding because they don’t want to use the toilets outside their home. Others ignore the urge because of emotional stress or because they are too busy. Children may postpone a voiding because of stress about toilet training or because they don’t want to interrupt their play.

Specific diseases

Some of the diseases that cause constipation are neurological disorders, metabolic and endocrine disorders, and systemic diseases that affect organ systems. These disorders can slow down the movement of stool through the colon, rectum or anus. Such diseases and conditions are:

  • Multiple sclerosis
  • Parkinson’s disease
  • Chronic idiopathic intestinal pseudo-obstruction
  • Spinal cord injuries

The metabolic and endocrine diseases that can cause constipation are the following:

  • Diabetes
  • An underactive or overactive thyroid gland
  • Uremia

Systemic disorders that can cause constipation are the following:

  • Amyloidosis
  • Lupus
  • Lyme disease

Colon and rectal problems

Intestinal obstruction, scar tissue (adhesions), diverticulosis, tumors, colonic stenosis, Hirschsprung’s disease and cancer can compress or narrow the bowel and rectum and cause constipation.

Problems with bowel function, idiopathic chronic constipation

Also chronic idiopathic, of unknown cause, constipation, also known as functional constipation, is rare. However, some people are chronically constipated and do not respond to routine treatment. Chronic constipation may be associated with multiple problems related to hormone control or with the nerves and muscles of the colon, rectum or anus. Functional constipation occurs in children and adults and is more common in women.

Colonic inertia and delayed transit are two types of functional constipation, caused by reduced muscle activity in the colon. These syndromes may affect the whole colon or may be limited to the left or lower (sigmoid) part of the colon.

Functional constipation, resulting from abnormalities in the structure of the anus and rectum, is known as rectal dysfunction or animus. These abnormalities result in the inability to relax the muscles of the rectum and anus that allow stool to pass.