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  • Definitions (1) (2)
  • For something to be absorbed, it has to go through the absorptive pathway, which consists of the following:
    1. unstirred layer
    2. glycocalyx
    3. apical membrane
    4. cytoplasm
    5. basolateral membrane
    6. intercellular space
    7. basement membrane
    8. capillary or lymph wall

Protein absorption

  • Adults can absorb amino acids, di-peptides and tri-peptides
  • Neonates can absorb whole proteins by the process of pinocytosis (e.g., immunoglobulins)
  • Amino acids are absorbed by sodium-dependant carrier-mediated secondary active transport
  • There are a number of carriers in the basolateral membrane for amino acids

Lipid absorption

  • Fatty acids, free cholesterol, phospholipid products, fat soluble vitamins are all in micelles covered with bile salts
  • hydrophilic ends of bile salts point out, while hydrophobic ends point in
  • Micelles diffuse through the unstirred layer to touch the lipid membrane
  • lipophyllic components diffuse across membrane into cell down concentration gradients.
  • Bile salts are not absorbed until the distal terminal ileum
  • Short chain and medium chain triglycerides are sufficiently water soluble to be absorbed by diffusion
  • Patients with fat malabsorption are prone to deficiencies in the fat soluble vitamins (A, D, E, and K).
  • They may also be deficient in essential long-chain fatty acids

Transport processes