Absorption in the small intestine

Villi
1. Thin walls, lined with epithelial cells
  1. Short diffusion distance
2. Finger-like projections of the small intestine
  1. Increases surface area for absorption by diffusion
3. Has a rich network of capillaries
  1. Carry's away absorbed molecules to maintain a concentration gradient
4. Able to move
  1. Maintains steep concentration gradient
5. Epithelial lining has microvilli
  1. Increases surface area
Role of diffusion in absorption
1. Net movement of molecules/ions from a region where they are highly concentrated to a region when their concentration is lower
2. Concentration of glucose is greater in the lumen of the small intestine than in the blood
  1. Concentration gradient
    1. Maintained by circulation of blood
    2. Villi muscles contract and relax, mixing contents of small intestine
      1. Glucose-rich food is next to villi
Role of active transport in absorption
1. Diffusion only results in equal concentrations of glucose on either side of the intestinal epithelium
  1. Not all available glucose is absorbed
2. Glucose is absorbed by co-transport, it is drawn in with sodium ions (Na+)
3. Mechanism
  1. 1. The sodium-potassium pump transported 2 potassium ions in and 3 sodium ions out (to blood)
  2. 2. There is now a much higher concentration of Na+ in the lumen than epithelial cells
  3. 3. Sodium ions diffuse into the cell down their concentration gradient through a co-transport protein
  4. 4. As they move in they couple with glucose molecules, drawing them into the epithelial cell
  5. 5. Glucose then passes into the blood by facilitated diffusion
4. As sodium moves down it's conc. gradient, glucose moves up it's
  1. ATP is used in Na+/K+ pump
    1. Indirect active transport of glucose

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Absorption in the small intestine

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	Created by charharrison over 9 years ago