Ileum

• How is the ileum adapted for digestion?

  -Large surface area: mucosa is folded into villi, epithelial cells have microvilli

  -short diffusion pathway: thin, one layer of columnar epithelial cells

  -good blood supply: lots of capillaries, mantains the concentration gradient
• Where do glucose and amino acids in the ileum come from?

  Glucose from diet (digestion of starch)

  Amino acids from action of exopeptidases
• How are glucose and amino acids absorbed in the ileum?

  -initially by facilitated diffusion down a concentration gradient

  -when equilibrium is reached, co-transport is used

  1. Active transport of Na+ from cells into blood against concentration gradient, requiring ATP
  2. This lowers the Na+ concentration inside the cell
  3. Facilitated diffusion of Na+ down a concentration gradient
  4. Glucose/amino acid binds to the co-transport protein and will be absorbed into the cell as long as there is a Na+ conc gradient
  5. Facilitated diffusion of glucose/amino acid into blood
• Where are glucose and amino acids transported to after absorption in the ileum?

  Blood in villus capillary -> hepatic portal vein -> liver
• How are lipids absorbed in the ileum?

  -fatty acids and monoglycerides are absorbed into epithelial cell

  -triglycerides reform

  -forms chlyomicrons in the Golgi body

  -exocytosis of chlyomicrons into lacteal

  -chlyomicrons transported in lymph