Flashcards in Digestion and Absorption Deck (41):
What is the purpose of enterokinase?
It cleaves pepsinogen to pepsin
What enzymes come from the stomach?
What enzymes come from the pancreas
what enzymes come from intestine?
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?
How is glucose mainly absorbed: active or passive:
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?
What are the major three enzymes of triglyceride breakdown?
cholesterol ester hydrolase
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
What does phospholipase A2 do?
releases FA from the 2nd carbon of glycerol
What type of absorption is the most calorie intense absorption?
What does FABP do?
takes FA from the membrane to the SER, so you can maintain diffusion gradient
What happens once you bring the FA to the SER?
we resynthesize TG in SER, with fatty acyl CoA synthase. going from acyl coa -> DG -> TG. The lacteal then absorbs the TG
once the SER resynthesizes the TG, what happens?
They are taken to chylomicrons and released in the lymph by the lacteal
What are the four fat soluble vitamins?
What do we need to absorb B12?
IF in the ileum
How many liters of water does the duodenum and jejunum absorb?
In the colon, absorption of Cl is linked to secretion of what?
HCO3, which is why the stool water is very basic
What is secreted in the colon in exchange for Na?
What are the two types of diarrhea? what are the xauses of each?
osmotic - impaired absorption, accumulation of solutes, lack of enzymes, decreased absorptive surface, precipitation of bile salts, motility
secretory - increased secretion by crypt cells, bacteria: cholera, increased secretory hormones, increased adenylate cyclase, activation of apical Cl channels
What protein is needed for iron absorption?
Where are satiety signals integrated?
What are the two parts of the arcuate nucleus of the hypothalamus? what are their functions?
POMC - neurons secreting aMSH (INH intake and stimulate metabolism)
NPY - stimulated by hunger, does opposite
What does ghrelin do?
It stimulates food intake and the NPY and blocks the POMC
Source, site of action and effect of Insulin
pancreatic beta cells
decrease appetitei increase metabolism
Source, site of action and effect of leptin
hypothalamus, decrease NPY and increase POMC
decrease appetite and increase metabolism
Source, site of action and effect of cck
i-cells of duodenum
decrease appetite, decreased gastric empyting
Source, site of action and effect of pyy
L-cells of ileum and colon
increase gastric empyting