Digestion Physiology Flashcards
How are carbohydrates absorbed?
Only as monomers
Where are oligosaccharidases present?
They are integral membrane proteins facing the lumen of GI tract
How many substrates does Lactase have?
- Lactose –> glucose and galactose
What is the only enzyme that can split the branching in alpha limit dextrins?
Isomaltase
Whta is the rate limiting step in the action of lactase?
Rate of hydrolysis of lactose
What is the rate limiting step in the actions of maltase, sucrase and isomaltase?
Transport of released monomers
Causes of lactose intolerance
1) primary lactase deficiency/ primary hypolactasia - due to lack of lactose persistence LP gene
2) secondary lactase deficiency - damage/ infection to proximal small intestine
3) congenital lactase deficiency - rare autosomal deficiency
What are the substrates produced by colonic-microflora if lactose enters it from the ileum?
1) short chain fatty acids (can be absorbed)
2) H2 - detected in the breath of lactase deficient indv. after a lactose challenge
3) co2
4) methane
Consequences of the substrates formed due to lactose intolerance
Bloating
Abdominal pain
Flatulence
Consequences of undigested lactose are:
1) acidification of the colon
2) increased osmotic load - loose stools and diarrhoea
Where does the absorption of the final products of carbohydrate digestion occur?
In the duodenum and jejunum
How does the absorption of final pdts of carb. digestion occur?
Via a two step process of entry and exit from enterocytes via apical and basal membranes
How is the entry&exit of carb digestion final pdts mediated in the enterocytes?
ENTRY
1) SGLT1- secondary active transport used to absorb GLUCOSE & GALACTOSE
2) GLUT5- Facilitated diffusion for FRUCTOSE
EXIT
GLUT2 - Facilitated diffusion, Common for all the monosaccharides
How does SGLT1 operate?
1) binds to 2 Na+
2) increases affinity for glucose
3) gulcose binds to it
4) 2 Na+ dissociate
5) glucose affinity reduces
6) glucose dissociates
7) repeats
