When we take food, it goes through the process of chewing in the mouth with the help of tongue and teeth. In the mouth, there is secretion of saliva, which starts the process of digestion. The food then reaches the stomach through the food pipe where the gastric juice acts on it. The gastric juice contains many chemicals called the enzymes and acids that help in the breaking down of the food matter. It then moves on to reach the small intestines (Duodenum+Jejunum+Ileum) where absorption of the digestible food items takes place. The juices from the liver (bile) and the intestine help in this. The non-digestible food now goes to the large intestine. Here, 90% of the water gets absorbed. This semi-solid stool (feces) now moves out to the anal canal and the anus to be passed out.
Gradual accumulation of stool in rectum results in buildup of fecal matter there. Due to this accumulation, the pressure inside the rectum keeps on increasing. After it reaches about 18 mm of Hg the urge to pass stool occurs. Once this pressure increases beyond 55 mm of Hg the anal sphincter relaxes and the whole muscles of the rectum contract. We then voluntarily relax the external anal sphincter and the stool is emptied.
Movement of the Intestine
- Segmental movement: for mixing.
- Slow peristalsis: 9 moves/min.
- Mass action contraction: contents move fast. Defecation reflex: results in passage of stool.