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Flashcards in Protein and carb digestion Deck (13):

three major dietary carbohydrates

cellulose (dietary fiber, undigested in humans). Starch (amylopectin and amylose glucose polymers). Disaccharides (sucrose=glucose+fructose, lactose=glucose+galactose)


salivary alpha amylase: what does it do? what does it produce? Does it fxn in stomach?

hydrolysis of internal alpha 1,4 linkages (not alpha-1,6 or terminal alpha-1,4). Produces maltos, maltotriose, alpha dextrins. inactivated by gastric acid


Pancreatic alpha amylase: what does it do?

targets are same as salivary amylase.


where are most oligosaccharides broken down? by what and what secretes them? What are some examples?

brush border of upper jejunum. Enzymes secreted by enterocyte. Lactase, sucrase, maltase, alpha-dextrinase (debranches alpha-dextrins by cleaving alpha-1,6 branch points)


Mech of monosaccharide absorption for glucose and galactose? For sucrose?

SGLT (sodium dependent glucose transporter). Requires basolateral Na/K ATPase to create gradient then 2 Na brought in with each glucose.

For fructose you use GLUT5. Does not require Na. Goes through a carrier down its concentration gradient (facilitated diffusion)


How do the monosaccharides leave enterocyte

glucose and fructose both go out down their conc gradient via the GLUT2 carrier


three phases of protein digestion

gastric, pancreatic, intestinal (depending on source of peptidases)


what happens in gastric phase of protein digestion

acid denatures proteins, pepsin starts to break peptides down


Can you absorb di and tri peptides? how about di and tri saccharides?

yes (although most are absorbed as AAs); no


enteropeptidase: what secretes is and by what signal? Fxn?

intestinal mucosal epithelial cells upon CCK stimulation. Converts trysinogen to trypsin which then converts the other propeptidases


at what pH are the pancreatic peptidases active?

Neutral. They require bicarb secretion to neutralize stomach acid


How are most AAs absorbed?
How are peptides absorbed?

Na dependent mechanism.

Probably by a single transporter and are then degraded intracellularly. (very few peptides make it out basolateral side)


Is there ever intact protein absorption?

infants can absorb intact proteins. Important for immunity (mother's Ig).

In adults, M cells absorb whole proteins (for immune purposes, not dietary)