L10 - carbohydrates and protein absorption Flashcards
what can SI absorb that is a part of carbohydrates
- monomers of it
- some digestible polymers that can be broken down into monomers
what does dietary fibre consist of
insoluble and soluble fibres
what are the steps in digestion of carbohydrates
- luminal digestion or hydrolysis
2. membrane digestion
what happens during luminal digestion
- salivary and pancreatic amylase is secreted
- salivary amylase starts in the mouth but inactivated by gastric acid when the carbohydrates reach stomach
- pancreatic amylase induceed by CCK completes the starch digestion
how does amylase break starch into smaller ones
-hydrolyses internal glycosidic 1-4 linkages
at what points in the starch does the amylase cant; work on
- 1-4 linkages at the end
- 1-6 linkages
- 1-4 linkages that are next to 1-6 linkages
what molecules are made due to luminal digestion
- maltose, maltriose and a-limit dextrins (have 1-6 linkages )
- they are non absorbable
what happens during membrane digestion
SI has 3 brush border oligosaccharides which are enzymes; lactase, maltase and sucrase isomaltase
- they break oligosaccharides into disaccharides that can be absorbed
what bonds does the brush border molecules can break and what disaccharides are formed
all 3 - terminal 1-4 linkages
- maltase - makes glucose
- sucrase into glucose and fructose
- isomaltase - breaks 1-6 linkages in a-limit dextrins
how are glucose and galactose taken up by SI cell
- SLGT1, transporting glucose and galactose with Na ions
- glucose actively transported against its conc gradient
- Na transported in down its conc gradient due to Na ions pumped out by the pump
- this is secondary active transport
How is fructose taken up
via GLUT-5 transporter via facilatied diffusion
how does glucose, galactose and fructose exit the SI cell
via GLUT2 transporter
how does lactase deficiency affect the amount of glucose taken up
-less lactose is digested into glucose so there is a lower conc of glucose
what molecules proteins are digested into
oligopeptides and AAs before the uptake
how many pathways proteins can be taken up
4