Absorption

• where does absorption occur?

  it mainly occurs in the small intestine, by diffusion, facilitated diffusion and active transport
• why do epithelial cells have many mitochondria?

  as active transport needs ATP
• how is the ileum well adapted for absorption?

  • in humans, its very long, several metres, and its lining is folded
  • on the surface of the folds villi and their epithelial cells have microscopic projections called microvilli
  • the folds, villi and microvilli produce a very large surface area for absorption
• what is this an image of?

  a longitudinal section of ileum wall

  
• what is this an image of?

  a generalised structure of the ileum

  
• what are the layers of the small intestine wall?

  • mucosa - has villi; cells of villi have microvilli
  • submucosa
  • circular muscle
  • longitudinal muscle
  • serosa
• what is this an image of?

  epithelial cells of the small intestine

  
• what is this an image of?

  tissue layers in the small intestine wall

  
• what is this an image of?

  villi in the small intestine wall

  
• how are amino acids absorbed into the epithelial cells of the small intestine wall?

  • by active transport and, as individual amino acids, they pass into the capillaries by facilitated diffusion
  • they are water-soluble and dissolve in the plasma
• how does glucose pass into the epithelial cells of the small intestine wall?

  • it passes into the epithelial cells with sodium ions, by co-transport
  • they move into the capillaries, sodium by active transport and glucose by facilitated diffusion, and dissolve in the plasma
  • diffusion and facilitated diffusion are slow and not all the glucose is absorbed
  • to prevent it leaving the body in the faeces, some is absorbed by active transport
• how do fatty acids and monoglycerides diffuse into the epithelial cells and into the lacteals of the small intestine wall?

  • lacteals are blindly-ending lymph capillaries in the villi
  • they are part of the lymphatic system, which transports fat-soluble molecules to the left subclavian vein near the heart
• how are minerals taken into the blood in the small intestine wall?

  they are taken in by diffusion, facilitated diffusion and active transport and dissolve in the plasma
• what is this an image of?

  sodium and glucose absorption

  
• where are vitamins B and C absorbed into?

  they are water-soluble and are absorbed into the blood
• are vitamins B and C water-soluble or fat-soluble?

  water-soluble
• where are vitamins A,D and E absorbed into?

  they are fat-soluble and are absorbed into lacteals
• are vitamins A, D and E water-soluble or fat-soluble?

  fat-soluble
• how do fatty acids and monoglycerides transport from lumen into epithelial cell?

  through diffusion
• how do fatty acids and monoglycerides transport from epithelial cells into lacteals?

  through diffusion
• how do fat-soluble vitamins transport from lumen to epithelial cell?

  through diffusion
• how do fat-soluble vitamins transport from epithelial cells to lacteals?

  through diffusion
• how does glucose transport from lumen to epithelial cells?

  through facilitated diffusion in co-transport and also active transport
• how does glucose transport from epithelial cells into capillaries?

  through facilitated diffusion
• how do disaccharides transport from lumen to epithelial cell?

  through active transport
• how do disaccharides transport from epithelial cells into capillaries?

  as monosaccharides by facilitated diffusion
• how do amino acids, dipeptides and tripeptides transport from lumen into epithelial cells?

  through active transport
• how do amino acids, dipeptides and tripeptides transport from epithelial cells into capillaries?

  through facilitated diffusion
• how do minerals transport from lumen into epithelial cells?

  through facilitated diffusion
• how do minerals transport from epithelial cells into capillaries?

  through facilitated diffusion
• how do water-soluble molecules transport from lumen into epithelial cells?

  through active transport
• how do water-soluble molecules transport from epithelial cells into capillaries?

  through active transport
• how does water transport from lumen into epithelial cells?

  through osmosis
• how does water transport from epithelial cells into capillaries?

  through osmosis
• what is the fate of lipids?

  lipids are used in membranes and to make some hormones but excess is stored
• what is the fates of other molecules?

  other molecules are taken in the hepatic portal vein to the liver, after which their fates vary
• what is the fate of glucose?

  glucose is taken to body cells and respired for energy or stored as glycogen, in liver and muscle cells and excess is stored as fat
• what is the fate of amino acids?

  • amino acids are taken to the body cells for protein synthesis
  • excess can‘t be stored so the liver deaminates the amino acids and convert -NH2 groups to urea, which is carried in the blood and excreted at the kidney
  • the remains of the amino acid molecules are converted into carbohydrate for storage or conversion to fat