Egestion

The substances that remain unabsorbed by the intestinal mucosa and those which are not absorbable include bile pigments, calcium salts, some endoparasitic and symbiotic bacteria and other micro-organisms, water, certain salts and undigested fragments of food, form the residue or faecal matter which is passed in to the rectum (large intestine). A major part of water and certain, salts are absorbed from the rectum. So the matter becomes more or less solid. The wall of the rectum does not show regular peristaltic movement but occasionally shows spasmodic contractions at irregular intervals which cause the movements of the bowl ahead (posteriorly). The faecal matter is finally discharged out through the cloacal aperture when the sphincter muscles of the latter relax and the aperture is opened.