Digestion & Absorption Flashcards
Main contents of food?
- Carb
- Lipids
- Proteins
What are the two forms of digestion occurring in the small intestine?
- Luminal
2. Membrane
What is luminal digestion mediated by? Where is it secreted into?
Pancreatic enzymes, into the duodenum
What is membrane digestion mediated by? Where is it secreted into?
Mediated by enzymes situated at brush border of epithelial cells
What are enterocytes?
Absorptive cells of intestinal epithelium
What two membranes do the breakdown products have to cross to get into the interstittium?
- Apical
2. Basolateral
What is assimilation?
Digestion + absorption
What are the 3 types of carbohydrates?
- Polysaccharides
- Oligosaccharides
- Monosaccharides
Basic building blocks of carbs?
D dimer glucose monomers
Main chemical bonds formed in carbs?
- a-1,4
2. a-1,6
Can polysaccharides be absorbed into the gut?
No. Need to be broken down into monosaccharides for absorption
What is the sequence of carb breakdown?
Starch–> Oligosaccharides–> Monosaccharides
What is the action of A-amylase?
Endoenzyme
Breaks Internal a-1,4 linkages but not Terminal a-1,4 bonds. Hence no Glucose produced
What is the role of Oligosaccharidases?
Breaks down oligosaccharides along the lumen of GI tract
Role of lactase?
Lactose–> glucose + galactose
Role of maltase?
breaks a-1,4 bonds in oligomers
Role of sucrase?
Sucrose–> Glucose + fructose
What is lactose intolerance?
Unable to digest lactose. Due to enzyme lactase insufficiency.
What is primary lactase deficiency?
Lack of lactase persistence allele. Most common cause world wide
What is secondary lactase deficiency?
caused by damage to/ infection of proximal small intestine
What is congenital lactase deficiency?
Austosomal recessive.
Unable to digest lactose from birth
What are the effects of undigested lactose? (2)
- Colon acidification
2. increased osmotic load- diarrhoea, loose stool
What are the two types of glucose transporters in the intestine?
- Sodium dependent
2. Sodium independent
What is the important transporter of Sodium dependent transporters?
SGLT1
What does SGLT1 do?
active transport of Glucose and galactose across brush border
What are the sodium independent transporters?
GLUT 1-5
Role of GLUT5?
Transports fructose
What is the mechanism of SGLT1 (6 steps)
- 2 Na bind
- Glucose affinity increases, glucose binds
- Na and glucose translocate from extra to intracellular
- 2 Na dissociate, affinity for glucose falls
- Glucose dissociates
Repeat
What must proteins be converted to to allow digestion?
Protein–> oligopeptides-> amino acids
What are the two types of peptidases ?
- Endo- cleaves middle of chains
2. Exo- cleaves ends of chains
Subtypes of exopeptidase?
Carboxypeptidase A & B. Both produce single amino acids
What does HCL do in stomach?
Acid- denatures proteins
Role of pepsin in stomach?
Protein–> Peptides (main stomach enzyme, endopeptidase)
What are the two types of protein transporters needed for absorption?
- 5 Na dependent
2. 2 Na independent
Ho are amino acids absorbed into the basolateral membrane?
- Mediate efflux of amino acids, Na independent
2. Mediate Influx of amino acids. Na dependent
