Stool Formation

Stool Formation

Stools are formed in the colon during the last phase of Digestion. A well formed stool is soft and flexible. Measuring about 1.5” in diameter and about four to seven inches in length. Well formed stools are easily passed without straining.

Stools are formed from feces. Feces are the particles of waste matter that is left over after the body has processed and absorbed nourishment from the foods we eat. Feces contain water, dietary fiber, inorganic salts, dead cells, bacteria, and anything the body cannot or will not absorb.

Feces first enter the colon in liquid form. During digestion, chemical and muscular actions work toward changing the foods we eat into a nutrient-rich-liquid called chyme. 90% of nutrient absorption takes place across the surface area of the 25 foot long small intestine (the other 10% is absorbed by the stomach and the colon). Villi, projections of mucosa lining the small intestine, absorb nutritive components from the liquid chyme and increase the surface area for absorption and digestion. The muscles that surround the small intestine contract and relax in a mild wavelike motion called peristalsis to move the chyme through the small intestine. After the nutrients are absorbed, the small intestine passes the remaining liquid into the colon through the illeocecal valve. At this point the liquid, formerly nutrient rich chyme, is now made up of waste particles - feces.

Through peristalsis, the muscles of the colon and the abdomen advance the liquid feces through the colon and compress the fecal matter into stools. During this process the colon extracts water from liquid feces as it is passed over the surface of the lumen (the interior) of the colon. The water is absorbed by the lumen, leaving the larger waste particles to be further tumbled along and formed into stools. This is somewhat similar to spraying down a sink or a side walk with water. The pressure and the water tumble the particles along. Particles that are heavier than water form piles of debris as the water is drained away. This debris is formed into stools.

Water and Dietary Fiber play critical roles in the formation of stools and in Healthy Bowel Function. Water can move across the intestinal mucosa of the lumen in both directions. While it is the job of the colon to extract water from the liquid feces, the Insoluble Fiber in the feces draws some of that water back into the stool from the lumen as the stool is formed. These fibers can swell up to 20 times their original size. The fluid these fibers retain creates volume and weight in the stool. Increased volume and weight stimulates muscle contractions. When these muscle contractions occur, stools move more quickly through the colon. Optimal movement of stool through the colon is referred to as Speedy Stool Transit Time. Movement that is too fast results in diarrhea, and movement that is too slow results in constipation. Through fermentation, healthy intestinal bacteria convert the Soluble Fiber present in the chyme, into a gel that becomes incorporated throughout the fecal mass as the stool is formed. This gel creates stools that are soft, flexible and easy to pass. Gel that is not incorporated into the stool nourishes the lining of the colon and nourishes the growth of healthy bacteria. A Healthy Colon Lining lubricates the passage of stools. This also contributes to speedy stool transit time.

Muscular activity, fluids, dietary fiber, bacteria, a healthy colon lining and speedy stool transit time work together to produce stools of good texture, volume, and weight that are soft, flexible and easy to pass without straining. A prompt response to the Defecation Reflex ensures this outcome.