9.5 - Defaecation

Functions of the Large Intestine

After absorption of the nutrients, the remaining content enters the colon. The intestinal contents consist of mixtures of water, undigested food, indigestible fibres as well as dead cells and bacteria. The two main functions carried out by the large intestine are water and minerals reabsorption and formation of feces.

Colon

• Reabsorption of water and minerals and other metabolic byproducts such as vitamin B, vitamin K and folic acid.
• Absorption of water from undigested remains result in the formation of feces.
• Feces consist of indigestible food remains, dead cells and other waste products like bile pigments, bacteria and toxic substances.
• Mucus secretion from the wall of the colon aids the movement of feces along the colon.

Rectum

• It takes 12 to 24 hours to pass the feces to the rectum.
• As the feces accumulate, pressure in the rectum increases, causing a desire to expel feces from the body.
• The muscles of the rectal wall will contract to expel the feces via anus.
• This process is called defecation.