The Ecology of Humans (37) Completing Digestion

Completing Digestion

The large intestine is the final passage of undigested food out of the body. The large intestine has a smooth mucosal lining, lubricated by mucus to ease the passage of waste.

The bowels start with the cecum, which has the ileocecal valve: a one-way passage from the small intestine and the appendix. The valve’s critical function is to limit reflux of colonic contents back into the small intestine.

The S-shaped colon follows. At the terminal end is a 15-cm exit pipe: the rectum, which is capped by an instinctually controlled round muscle, the anus.

All the blood coming through the intestinal tract, including the bowels, is filtered through the liver. Disorders or imbalances in the lining of the intestinal tract impact the liver.

Water is suctioned from waste product in the colon, solidifying into stool. But the colon is more than a mere receptacle of waste.

The colon hosts a tremendous thriving variety of microbial colonies: of bacteria, fungi, yeast, and others. There are 1.4 kilos of bacteria in a healthy person’s colon.

Metabolism in the colon is active. Bacteria in the colon further break down the waste there. 1/3rd to 1/2 of the weight of feces is made up of these microbes which are important in creating the texture of stool, and in maintaining the condition of the intestinal wall. Among their many nutritional contributions, colon bacteria produce B vitamins, which are critical to health.

Only certain strains of bacteria are suitable agents of digestion. Exactly which bacteria thrive in the large intestine greatly depends on what is eaten.

If the delicate symbiosis between digestive bacteria and its host is disrupted, or if there is outsized growth of undesirable microorganisms in the intestine, the protective barrier provided by the intestinal lining can break down.