- The second part of the small intestine is the ileum.
- The wall of the ileum is covered in millions of tiny bumps called villi.
- Villi increase the area of the wall surface in contact with digested food to allow easier absorption of nutrients into the blood stream.
- Each villus has a blind tube, lacteal, in the centre. Insoluble fatty acids are absorbed there and travel in the lymph vessels to the blood stream.
During absorption, small molecules move from the digestive into the circulatory system.
The next step is assimilation where small molecules move into the body cells. Some materials like glucose can be used immediately while others must be transported to the liver first and modified.
As undigested material move along the large intestine (colon), water, minerals and other useful materials are absorbed into the bloodstream. Undigested material become firmer to form faeces which is egested (excretion).