AS biology Unit 1 - Absorbtion in the small intestine

Thin walled

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

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.

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)