Co-transport of monosaccharides and amino acids

• What is co-transport?

  When two substances are transported together in the same direction into or out of a cell through a carrier protein in the cell membrane
• Why do monosaccharides and amino acids need to be transported across the villi by co-transport?

  Absorption cannot be achieved by diffusion alone, and co-transport allows monosaccharides and amino acids to be transported into ileum epithelial cells against their concentration gradient.
• Describe how monosaccharides or amino acids can be absorbed into the ileum epithelial cells by co-transport.

  1. Sodium ions are actively transported out of epithelial cells & into the blood through a Na+/K+ pump against the conc. gradient
  2. Low conc. of Na+ inside epithelial cell -> maintains a steep conc. gradient of Na+ between lumen of ileum & epithelial cell
  3. Na+ moves into epithelial cell down it's conc. gradient. Na+ moves into cell with glucose
  4. Glucose moves into blood, down it's conc. gradient, via facilitated diffusion.
• How are glucose and amino acids absorbed?

  Via co-transport in the ileum