Villi and Microvilli
Lined with epithelial cells
Rich network of blood cappillaries
Villi regulary contract and relax to mix contense of the small intestine
Increase the surface area for diffusion
Able to move to maintain the concentration gradient
Microvilli are projection from the epithelial cell lining on the villi
Microvilli are 1000 times smaller than villi
The role of diffusion in absorption
Glucose travels DOWN the concentration gradient from the small intestine into the blood
The constant flowing of the blood and glucose being removed and used up by cells in respiration helps maintain the concentration gradient
Muscles in the villi regualary contract and relax to mix the contense of the small intestine so ensure glcose rich food is replacing the glucose bein absorbed.
How does active transport occur in the small intes
1) Sodium ions are activiy transported out of the epithelial cells by the sodium-potassium pump into the blood. This takes place in a protein-carrier moelcule found on the cell surface of the epithelial cell.
2)There is now a higher concentrtion of sodium ions in the lumen than the epithelial cells.
3)The sodium ions diffuse into the epithilial cell down the concentration gradient through a co-transport protein in the cell surface membrane
As the sodium ions flood back in through the co -transport protein they couple with glucose molecules which they carry into the cell with them
4) The glucose passes into the blood plasma by facilitated diffusion using another type pf carrier protein
Sodium molecules move down the concentration gradient, glucose molecules move up. The sodium movement power the glucose movement rather than it directly being ATP ( indirect active transport)