Digestion and Absorption Flashcards
What is the purpose of enterokinase?
It cleaves pepsinogen to pepsin
What enzymes come from the stomach?
pepsin
What enzymes come from the pancreas
amylase trypsin chymotrypsin carboxypeptidase lipase-colipase phospholipase a Cholesterol esterase
what enzymes come from intestine?
enterokinase disaccharidases maltase sucrase lactase trehalase isomaltase peptidases
What is the most important part of the small bowel?
ileum, otherwise you can remove up to 60-70% and be fine.
Explain the changes of tight junctions in the small bowel as you go down
In the duodenum, the tight junctions are fairly loose.
once you get to the ileum, they are very tight.
What does amylase do? what type of link does it target?
Amylase digests to maltose and maltotriose.
Amylase targets 1:6 links
What is the most common disaccharide?
sucrose
How is glucose mainly absorbed: active or passive:
active
What are the three transporters for carbohydrate absorption? what are each’s actions?
SGLT1 - two Na and Glucose/Galactose
GLUT2 - exits for glucose, galactose, and fructose (all three competing for access to glut2 to exit luminal cell)
GLUT5 - fructose absorption
What is the first stage of protein degradation?
pepsin (breaks peptide border), breaking them into di/tripeptides, large peptides and free amino acids
where is trypsin cleaved?
cleaved in the brush border by enterokinase
How are carboxypeptidases A and B different from the other peptidases?
They only cleave off one enzyme at a time.
Explain the actions of trypsinogen
Trypsinogen is cleaved by enterokinase to trypsin. Trypsin then activates more trypsin, chymotrypsin, elastase, and carboxypeptidases A and B
How big can protein particles be to be absorbed in the small intestine?
at most, tripeptides. do not leave the lumenal cell until they are individual amino acids
When there is an absence of carriers for a basic amino acid, how do we absorb them?
We absorb them as dipeptides still so we can obtain that nutrients.
What is hartnup’s dz due to?
a lack of neutral amino acid carriers
what can result from hartnup’s dz?
phellagra
What are the major three enzymes of triglyceride breakdown?
pancreatic lipase
cholesterol ester hydrolase
phospholipase A2
Explain the actions of pancreatic lipase (long answer)
Secreted as active substance. Breaks triglycerides, specifically on 1 and 3 arms. Yields 2 FAs and a monoglyceride.
Also acts on emulsion droplets, secreted 1:1 with colipase (not an enzyme) and binds to droplets displacing a BA, allowing PL to bind to emulsion droplet
Additionally binds to micelle to keep TG source nearby
What are the actions of cholesterol ester hydrolase?
specific for all links of TG
nonspecific
What does phospholipase A2 do?
releases FA from the 2nd carbon of glycerol
What type of absorption is the most calorie intense absorption?
lipid absorption
What does FABP do?
takes FA from the membrane to the SER, so you can maintain diffusion gradient
