Gloucose and absorption- saccharides

Monosaccharides - Glucose, Fructose, Galactose

Basic monomer unit - sugar
Soluble, sweet-tasting

Disaccharides - Maltose, Sucrose, Lactose
2 monosaccharides joined by glycosidic bond
Glycosidic bond formed by removal of 1 molecule water
Can be separated into constituent monosaccharides by hydrolysis

Polysaccharides - Starch, Cellulose, Glycogen
Held together by glycosidic bonds, formed by condensation reactions
Large, insoluble, suitable for storage or support

Absorption in the Small Intestine

Diffusion in Absorption

Net movement of molecules from high to low conc
Carbohydrates digested continually
Higher conc of glucose in SI than blood = concentration gradient
Blood constantly circulated = glucose absorbed, constantly removed by cells for respiration, maintains concentration gradient

Villi

Finger-like projections in SI walls, thin walls with rich capillary network on one side and epithelial cells on the other

Adapted for absorption of digested products:

·         Large surface area, fast diffusion rate

·         Thin walls, shorter diffusion path, fast diffusion rate

·         Ability to move, maintain diffusion gradient

·        

Rich blood supply, maintain concentration gradient

Role of Active Transport in Absorption

Diffusion can only equalise concentrations on each side - dynamic equilibrium
Therefore, not all available glucose is absorbed, and some may pass out of body

Active transport stops this from happening!

Glucose is absorbed by the co-transport mechanism, using a co-transport protein and the energy from the sodium ion concentration gradient so that it moves up its own concentration gradient.

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