Flashcards in Ward II Deck (75)
What are the 3 ways in which the SI has such a large surface area?
1. Circular concentric Kirkring folds 3X
2. Intestinal Villi 30X
3. Each enterocyte on the villi has microvilli (brush border) 600X
What is an important thing that is associated w/ the brush border of intestinal enterocytes?
this is the location for numerous enzymes that break down proteins & carbs in their final stages before absorption.
Its a perfect location right next to where they will be absorbed...otherwise all the little breakdown products could create an osmotic gradient & diarrhea.
What is each villus equipped with? Why is this so important?
its own blood & lymphatic supply (Lacteal)...this ensures optimal removal of peptides, AA, sugars, & fats.
What is segmentation & why is it important in the small intestine?
It is contraction of the circular muscles of the small intestine so that chyme is moved back & forth & gets max exposure to digestive enzymes.
There is a gradient of the segmentation contractions...highest frequency in duodenum & lowest frequency in ileum. After all, we need the chyme to move downwards.
T/F Cellulose is a carb that can be broken down in the human GI system.
False. Can't be broken down in human GI.
What are the 3 major sources of carbs in food?
1. Disaccharides: sucrose, lactose etc
2. polysaccharides: starches
3. Other: amylose, glycogen, alcohol, lactic acid
What is the first thing to initiate carb breakdown?
mastication & salivary secretions
includes oral amylase: 3-5% of carb hydrolysis
Does hydrolysis of carbs happen in the stomach?
30-40-% of starch hydrolysis happens here after like an hour...it is broken down into maltose
Do pancreatic secretions contribute to hydrolysis of carbs?
Of course! Glad you asked...
alpha amylase is secreted by the pancreas, more powerful than oral amylase...
hydrolyzes carbs & produces maltose, maltotriose, & alpha-limited dextrins.
Where does the final breakdown of carbs before absorption happen? Why is this important?
It occurs @ the brush border (microvilli on enterocytes of villi). Here there are a bunch of enzymes...right next to transporters for glucose & galactose.
Important to absorb as soon as broken down:
prevents osmotic gradient-->diarrhea
prevents feedback inhibition of the breakdown
What are the 4 important enzymes that are on the brush border of the SI? Which of these are capable of being upregulated?
turns lactose-->glucose + galactose
alpha-dextrinase: non-specific dextrin enzyme
Sucrase: sucrose-->glucose + fructose
Maltase: maltose-->2 glucose
**sucrase & maltase can both be up-regulated.
Describe in detail how glucose is absorbed @ the brush border.
SGLT1 is a cotransporter @ the brush border that uses the energy of sodium going down its conc'n gradient to absorb glucose. Thus, glucose & Na+ go into the enterocyte. A Na+/K+ pump on the basolateral side of the enterocyte pumps Na+ out. Glucose is transported out of the enterocyte by a basolateral transporter, Glut 2.
Describe in detail how galactose is absorbed @ the brush border.
SGLT1 is a cotransporter @ the brush border that uses the energy of sodium going down its conc'n gradient to absorb galactose. Thus, galactose & Na+ go into the enterocyte. A Na+/K+ pump on the basolateral side of the enterocyte pumps Na+ out. Galactose is transported out of the enterocyte by a basolateral transporter, Glut 2. "
Describe in detail how fructose in absorbed @ the brush border.
Glut 5 is a transporter on the apical side of the enterocyte @ the brush border. It takes fructose into the enterocyte. Glut 2 allows fructose to leave the enterocyte on the basolateral side.
What percentage of caucasians have a lactose intolerance--lactase deficiency?
Of Jews, Arabs, American Indians?
Of Blacks, orientals, eskimos?
60% of Jews, Arabs, American Indians
70-95% of Blacks, Orientals, Eskimos
What causes the diarrhea & flatulence experienced w/ patients who are lactose intolerant?
the lactose can't be absorbed & some of the lactose is broken down into lactic acid by intestinal bacteria
These 2 factors create an osmotic diarrhea.
Also, the intestinal bacteria breaking down lactose into lactic acid produces gas. Thus, the flatulence.
How can you test for lactase deficiency?
A bunch of lactose
test blood levels for glucose. If lactose can't be broken down to produce glucose & galactose...then you won't find glucose in the blood at higher levels.
Why are dietary fibers important?
They help to add to the bulkiness of stool & reduce their transit time.
What's the problem with longer transit time of feces?
Well, I'm glad you asked...Carcinogenic bile acids cause colonic cancer. An example of carcinogenic bile acids is lithocholic acid. This is formed by the deconjugation of chendeoxycholic acid by luminal bacteria. When you reduce transit time you reduce the formation of these acids. You reduce the risk of colon cancer. Yay for dietary fiber!
Proteins have to be digested before they are absorbed...with one exception? What is it?
gamma globulins in mother's milk eaten by newborns...directly absorbed w/o digestion
What are 3 main sources of the protein our body deals with?
2. Protein that is sloughed off by intestinal mucosa
3. enzymatic proteins that are secreted
Are all of the pancreatic enzymes that are secreted into the intestine digested & excreted in feces?
most are absorbed by pinocytosis & recycled to the pancreas
Where is most of the protein absorbed in the GI? How much of the absorbed protein is AA? How much of it is short peptides?
It is absorbed in the SI, usually absorbed in the jejunum.
Short Peptides: 60-70%
What are the 3 types of protein transport?
Neutral AA: absorbed @ large conc'n
Basic AA: actively absorbed at small conc'n
Acidic AA: metabolized prior to absorption
What types of enzymes first break down proteins?
pancreatic proteases: trypsin & chymotrypsin & carboxypeptidase
What types of enzymes break down proteins @ the brush border?
What type of transport gets peptides & free AA into enterocytes? What type of transport gets it from the enterocytes into the bloodstream?
AA---> Cell: Active transport
Cell-->Blood: facilitated diffusion
How is trypsinogen (released by the pancreas) activated? What does it do once it's activated?
Enterokinase is a brush border enzyme in the duodenum. It activates trypsinogen to trypsin. Trypsin then activates a bunch of pancreatic enzymes, including trypsinogen!! Way to give back, buddy. : )
What are endopeptidases? What are 3 examples? What do they specifically break down?
Endopeptidases are enzymes that break down interior peptide bonds of proteins
Trypsin: targets ones w/ basic C terminal ends
Chymotrypsin: targets ones w/ aromatic C-terminal ends
Elastase: targets ones w/ neutral C-terminal ends