The ileum is the site of absorption for the end products of digestion:

1. Monosaccharides
2. Amino acids
3. Monoglycerides (like glycerol) and fatty acids

The ileum has a folded wall lined with finger-like projections called villi. Villi are lined with epithelial cells and are beside a network of capillaries.

1. Large surface area, increased by microvilli - increases rate of diffusion
2. Thin walls - reduce diffusion distance
3. Extensive capillary network - blood carries absorbed nutrients away maintaining a concentration gradient
4. Muscles contract and mix content - helps maintain concentration gradient

Co-transport is when two substances are transported together in the same direction into or out of a cell through a carrier protein in the plasma membrane.

All monosaccharides and amino acids need to be absorbed, which could not be achieved by diffusion alone.

Co-transport allows monosaccharides and amino acids to be transported into ileum epithelial cells against their concentration gradient.

1. Sodium ions are actively transported out of the ileum epithelial cells
2. This creates a steep sodium ion concentration gradient
3. The monosaccharides or amino acids are co-transported with sodium ions from the ileum lumen into the epithelial cells

When micelles contact ileum epithelial cells, the micelles break down and release monoglycerides and fatty acids.

Monoglycerides and fatty acids are non-polar.

This means they can easily diffuse through the non-polar plasma membrane into ileum epithelial cells.

Inside ileum epithelial cells, monoglycerides and fatty acids are recombined into triglycerides and form chylomicrons.

1. The chylomicrons leave ileum epithelial cells by exocytosis
2. The chylomicrons enter lacteals
3. The chylomicrons then travel through lymph vessels to the circulatory system