Function of the small intestine 1. Digestion Most of our food is digested in the small intestine. The first section of the small intestine produces many digestive enzymes. Two other organs, the liver and the pancreas, release substances into the small intestine to aid digestion. The liver produces a greenish fluid called
bile. It is stored in the gall bladder. Bile does not contain enzymes. Bile breaks up fats into smaller droplets, making them easier to digest. Bile also neutralises the acidic chyme from the stomach. The pancreas releases a digestive juice
called pancreatic juice into the first section of the small intestine. This digestive juice contains many enzymes. Pancreatic juice is alkaline which neutralises the acidic chyme from the stomach. The liver and pancreas release their products into the small intestine through small tubes called ducts.
One cell thick
Capillary
Gall bladder Liver
Pancreas Bile duct
Small intestine Pancreatic duct
Fig. 13 Bile from the liver and pancreatic juice from the pancreas are released into the small intestine.
2. Absorption Nutrients are absorbed into the bloodstream from the second part of the small intestine. Nutrients pass through the villi into the bloodstream. Once absorbed into the bloodstream, food molecules
are transported to the liver. The liver processes the nutrients, storing some and releasing others into the bloodstream to be transported to various parts of the body where they are used for growth and repair. The liver also releases waste products into the blood to be transported to the kidneys (excretory system) where they are removed from the body. The liver also breaks down other toxic substances like alcohol. When food molecules are delivered to the cells they
are used for energy, growth and repair. This is called assimilation.