The colon

The colon

The colon is the last five feet or so of intestine, and is called the large intestine. Its function is two-fold: it stores wastes which have passed out of the small intestine it absorbs water, certain salts such as sodium and potassium, and certain fat-soluble vitamins such as Vitamins A, D,E, and K. Besides that it has no digestive function other than the maintenance of body water and the elimination of waster. There can be few calories produced by bacteria in the colon breaking down complex carbohydrates which the body can use, but this essentially negligible compared to the calories absorbed in the small intestine.

The colon is anatomically divided into four parts. The ascending colon starts in the right lower quadrant of the abdomen, of which the cecum and appendix are a part. It ascends to just beneath the liver where it takes a sharp turn to the left and becomes the transverse colon. When it arrives at an area just below the spleen, it turns down and becomes the descending colon. The colon between the descending colon and the rectum is called the sigmoid or S-shaped colon. The rectum is actually a short fifth segment and ends in the anus. Hemorrhoids are varicose veins around the anus which can cause severe anal pain, bright red bleeding or blood tinges on the stool, or even anemia if the bleeding is severe enough.

One of the most common complaints in primary care medicine is constipation. This defined by hard, pellet like-stools which are hard to express, or by having three or less bowel movements per week. If this is acute, i.e., a recent change, it can be due to a blockage such as a colon cancer or appendicitis. There is a condition where infants are born with no nerve ganglions in certain segments of the colon causing a blockage called mega colon. The typical American diet is often deficient in these, especially the fiber which is found in fresh fruits and vegetable and whole wheat bread and cereal. The patient is instructed and guided in improving fiber content in the diet. A lot of people simply don’t drink enough water, and a good guide to proper intake is about six glasses of water a day. There is medical product called polyethylene glycol which causes more water to be delivered to the colon. Similarly, there is lactulose, a complex sugar which the body cannot digest, and it carries water to the colon as it passes down the intestinal tract.

There is another condition which causes a lot of discomfort in the general patient population called irritable bowel syndrome, or IBS. People who have this have cramps, a lot of intestinal gut sounds, variable bowel movements from constipation to diarrhea over consecutive days, and several other irritable symptoms. The severity of symptoms most often correlated with the amount of emotional stress the patient perceives. The condition is thought to be an overactive intestinal nerve condition much the way overactive nerves cause fibromyalgia in skeletal muscles. Treatment includes optimizing the diet for fiber and water, looking for food intolerance and allergies such as lactose intolerance, and therapy to reduce perceived stress. Medicines used include tricyclic antidepressants, antispasmodics, peppermint capsules, and other similar medications. IBS most often does not cause detectable blood loss in stool.
When lower intestinal bleeding occurs, either as black tarry stools characteristic of upper GI bleed such as a stomach ulcer, bright red bleeding, or even blood which can only be detected by a chemical test, other conditions come to mind which can potentially be serious in nature. One such condition ulcerative colitis in which (only) the colon mucosa brittle, ulcerated and bleed easily. Another condition is Crohn’s Disease which can cause regions of inflammation anywhere along the intestinal tract including the colon. These conditions have many supposed etiologies, but most clinicians see them as immune disorders where the body is actually attacking the colon or the entire intestinal tract. Treatment often consists of immune modulators, but sometimes surgery is necessary. Physicians are able to directly observe the mucosa of the colon with the procedure called colonoscopy. (A flexible, small diameter tube with a camera on the end is worked around to the beginning of the colon.)

A distinct case of colon obstruction and bleeding is colon cancer. It is responsible for the third most common cancer deaths in this country. Colon cancer begins in colon polyps which are fleshly growths of colon mucosa which begin as benign. The polyps can be snipped out during routine colonoscopy and thus prevent cancer. Once it becomes caner it usually spreads to the colon lymp nodes but is still treatable by surgery. Once it spreads to other organs like the lungs or liver, treatment can extend life, as by chemotherapy or radiation, but the cancer is usually not curable. Experts in the field of this disease estimate that 28,000 cancer deaths a year could be prevented by routine colonoscopy (Initial colonoscopy at 55 if there are no other risk factors, and every three to five years thereafter.)

Another cause of rectal bleeding and abdominal pain is diverticulitis. Diverticulae are tiny appendix-like pouches which protrude through the inside muscle layer of the colon. Just having diverticulae is a condition, not an illness, and they are very common in the general population. When they become inflamed or infected, illness begins. If they burst, the condition can be life-threatening. The appendix illness can be similar except the appendix is actually a tubular pouch-like organ off the beginning of the colon. It requires rapid surgical removal once diagnosed, whereas diverticulitis can often be treated with bowel rest, intravenous fluids, and antibiotics.

So, be kind to your colon. Eat fresh, and be sure your food contains a lot of fiber. Drink adequate amount of water. Avoid foods that irritate the colon like lactose if you are lactase deficient. Modulate or refrain from excessive alcohol use. See you physician if you have rectal bleeding, persistent diarrhea, fatigue and fever, or any significant change in bowel habits. Plan to get your routine colonoscopy: it’s slightly uncomfortable, but the peace of mind gained by having the procedure is well worth it.

John Drew Laurusonis M.D
Doctors Medical Center