co-transport

• main place where co-transport occurs is the absorption of glucose into the blood from the small intestine
• co-transport: absorption of glucose (facilitated diffusion)

  1. after digestion, there is a high concentration of glucose in the lumen
  2. glucose moves down the conc. gradient into the epithelial cells then into the bloodstream by facilitated diffusion via carrier proteins
  3. overtime the conc. gradient falls so the rate of facilitated diffusion falls
  4. so facilitated diffusion can not absorb all the glucose molecules
  5. so active transport is used to absorb the remaining glucose
• co-transport: absorption of glucose (active transport)

  1. sodium-potassium pump is embedded in the epithelial cell membrane - actively transports Na+ ions into the blood and K+ ions into the epithelial cell
  2. now there is a low conc. of Na+ ions in the epithelial cells and a high conc. of Na+ ions in the lumen
  3. this creates a concentration gradient
  4. Na+ ions in the lumen move into the epithelial cell by co-transport/facilitated diffusion, bringing glucose with it by active transport
• co-transport process:

  • epithelial cells contain lots of mitochondria -> provide ATP for active transport
  • membrane of epithelial cells folded into large number of microvilli -> increases the surface area of the membrane so more space for carrier proteins
  • glucose molecules carried away quickly in bloodstream -> maintains a steep concentration gradient
• proteins change shape to move molecules/ions across the membrane