lecture 11 - GI absorption Flashcards
What is the rate of GI absorption directly porportional to?
Surface area of the gut lumen
What is GI absorption?
Net passage of substance from lumen of gut, across epithelium, and into the interstitial fluid
Which motility pattern aids in GI absorption?
Segmentation
What are the 5 key factors that affect absorption in the GI tract?
Surface area, motility, adequate digestion, penetration, removal of substances from interstitial space
Why is it important for GI absorption to remove substances from the interstitial space?
Ensures a concentration gradient can be maintained so that substances can be moved from epithelial cells
What substances are absorbed in the stomach?
Ethanol, aspirin - nil nutritional absorption
What substances are absorbed in the colon?
Water, sodium, vitamins, short chain fatty acids, etc.
Is GI uptake of sodium selective or non-selective?
Non-selective, all sodium is taken up (if transporters are available) and kidneys maintain the balance in the flood by removing excess
Where are carbohydrates absorbed in the GI tract?
Duodenum, jejunum of the small intestine
What enzyme breaks polysaccharides into disaccharides?
Amylase
What converts disaccharides to monosaccharides in the GI tract?
Enzymes on the brush border of the small intestine
What transport mechanism is mostly used to absorb carbohydrates in the GI tract?
Na co-transport
What enzymes are used to to break down proteins in the GI tract?
Proteases (pepsin, trypsin, chymotrypsin), peptidases
What is the function of brush-border peptidases in the small intestine?
Break peptides down into single amino acid for absorption
How are amino acids absorbed in the GI tract?
Via co-transport with sodium
Where is calcium absorbed in the GI tract?
Duodenum
Where is iron absorbed in the GI tract?
Proximal duodenum
Where is vitamin B12 absorbed in the GI tract?
distal ileum
Where are fat soluble vitamins absorbed?
In the small intestine, where they diffuse with lipids across the epithelium
What are the 5 stages of lipid digestion?
- Emulsification
- Stabilisation
- Digestion
- Micelle formation
- Micelle absorption
What is used to emulsify lipids?
Bile salts
What enzyme is used to break down fats?
Pancreatic lipase
What are micelles of fat repackaged into in the cells of the gut wall?
Chylomicrons
How are chylomicrons transported away from the GI tract?
Via lymphatics from lacteals
