Digestion and Absorption Flashcards
Two types of digestive enzymes
Luminal: cavital digestion
Membrane bound
Exopeptides
Carboxypeptidase A and B
Endopeptides
Trypsin, chymotrypsin, elastopeptidase
What activates trypsin
Enterokinase
Barriers to absorption
Unstirred layer
Apical membrane
Cytoplasm of cell
Lots of membranes
What linkages can humans break down
Only Alpha linkages
What is starch broken down into
Maltose, Maltotriose, Alpha limit dextrin
What can starch not be directly broken down into? what is needed to make what it can’t?
Free glucose
Membrane bound enzymes further needed
What sugars are directly broken down by their own enzymes
Lactose, Sucrose, and Trehalase
3 final products of sugar digestion
Glucose, galactose, fructose
Two types of carb absorption
Diffusion component: anaerobic, very small amount
Active transport: aerobic, larger portion
3 carriers involved in sugar absorption
SGLT-1: Na and glucose or galactose
GLUT-5: Fructose alone
GLUT-2: Sends out Glu, Gal, Fru
How much protein digestion comes from gut secreted proteins
1/3
Most efficient type of protein absorption
Di and trip peptides
how do free aa get absorbed
via specific carriers
First step of fat absorption
Emulsification via bile acids and bile salts
What does colipase do
Binds lipase and a fat droplet to allow the two to come together
What allows fats to cross unstirred layers
Micelles
Major fat absorbing enzyme? What does it make
Pancreatic lipase
Makes two monoglycerides and a FFA
What does cholesterol hydrolase make
Cholesterol and glycerol
Two things needed to digest B12
Intrinsic factor and R protein
2 routes of fluid absorption
Paracellular
Transcellular
What brings absorption back to tonicity in the colon
More NaCl absorbed than water but bacteria brings back to tonicity
All methods of Na absorption are dependent on?
Na/K pump to make Na gradient
What is exchanged for chloride in colon
Bicarbonate (what makes feces alkaline)
What is exchanged for Na in colon
Potassium
Why doesn’t water follow Na in the colon
Junctions are too tight
Chronic mediator that increases metabolism and decreases food intake
POMC
Short term mediates that increase food intake and decrease metabolism
NPY and AGRP
Two things that stimulate POMC
Leptin and insulin
