GCSE Biology: The Small Intestine
How the small intestine is adapted for absorbing and digesting food.- It is very long, about 5m in an adult. This gives plenty of time for digestion to be completed, and for nutrients to be absorbed.
- It has villi. Each villus is covered with cells that have even smaller projections on them, called microvilli. This gives the inner surface of the small intestine a very large surface area, and so food can be absorbed more quickly./li>
- Villi contain blood capillaries. Digested food passes into the blood, to be taken to the liver and then around the body.
- Villi contain lacteals, which are part of the lymphatic system. Fats are absorbed into the lactels.
- Villi have walls only once cell thick. The digested food can easily cross the wall to reach the blood capillaries and lactels.
Mucus is secreted from the stomach by special cells which make mucus. There is a layer or mucus on the inside of the stomach to protect it from th e reactions.
Amylase is secreted in the mouth and the pancreas. It breaks down starch.
The epiglottis is a small flat that covers the opening of the trachea. It opens to let air in and closes when you swallow.
The walls of the stomach secrete hydrochloric acid to kill bacteria and create good conditions for pepsin to work in.
The duodenum, jejeunum and ileum make up the small intestine. In the duodenum bile and pancreatic juice are secreted.