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57 Cards in this Set

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  • Back
What allows for amplified mucosal surface area?
Cylinder intestine - has circular folds - have villi - have microvilli
What is the purpose of amplified SA? how much is it amplified?
600x; for increased absorption.
Where does most absorption occur in the GI tract?
In the duodenum in the small intestine.
What are 4 exceptions to where absorption occurs?
1. Asprin (stomach)
2. Alcohol (stomach)
3. Water (lg intestine)
4. Electrolytes (lg intest)
What are the types of carbs that are seen by the GI tract?
1. Polysaccharides
2. Disaccharides
3. Monosaccharides
What are Polysaccs?
What are the 3 types?
Long strings of simple sugars
-Starch from plants
-Glycogen from animals
-Cellulose from plant cell walls, undigestable/bulk fiber
What are Disaccs?
What are the 3 types?
broken down poly's, into 2 simple sugars.
-Sucrose (table sugar)
-Lactose (milk)
-Maltose (starch)
What are the 3 monosaccs?
Glucose Fructose and Galactose.
-The only carbs that can be absorbed.
Where does carb digestion begin, by what action?
In the mouth via salivary amylase.
What does amylase do?
breaks poly into disaccs
What happens to carbs in the stomach?
nothing; salivary amylase is inactivated by stomach acid.
What 2 enzymes act on carbs in the small intestine?
1. Pancreatic amylase
2. Epithelial disacchaaridases
What do epithelial disaccidases do?
break disaccs into monos.
Where are epithelial disaccharidases located/
in the cell membrane of epithel cells lining the GI tract in the small intestine. NOT secreted.
How is Glucose absorbed from the duodenal lumen?
1. Na+ is absorbed into the blood via Na/K pump
2. Low Na+ in enterocyte makes Na+ in lumen move down conc gradient;
3. Glucose moves with Na+ via 2ndary active transport.
4. Glucose moves down its conc gradient, absorbed into the blood.
How does glucose move from the enterocyte to the blood?
Via facilitated diffusion with a carrier molecule.
What are the 3 types of lipids?
1. Triglycerides (90%)
2. Cholesterol
3. Phospholipids
What is the structure of a tryglyceride?
-Glycerol backbone
-Fatty acid tails
-Cannot be absorbed
What digests tryglycerides into monoglycerides? How?
Lipases; cleave off 2 fatty acids to form a monoglyc.
Where does lipolysis occur?
(where is it most significant?)
-Mouth/stomach via salivary lingual lipase (small effect)

-Small intestine w/ pancreatic lipase and bile salts (most).
In what condition are fats absorbed from the GI lumen?
As broken down micelles
What 4 things come out of micelles after being broken down?
1. Monoglycerides
2. Free fatty acids
3. Cholesterol
4. Fat soluble vitamins A/D/E
When and where are bile salts absorbed?
LAST; in the ileum - not in the glob.
What happens to the broken down micelle contents in enterocytes?
They get repackaged into a glob with a lipoprotein coat, aka a chylomicron.
How do chylomicrons exit enterocytes?
via exocytosis.
Where do chylomicrons go after exocytosis from enterocytes?
NOT to the bloodstream; they get picked up by the lymphatic system, and THEN to the blood.
What is a protein?

What are polypeptides?
a long string of aa

shorter strings of aa
what are 3 types of peptides?
1. polypeptides (>3 aa)
2. Tripeptides
3. Dipeptides
what enzymes break down proteins, and where?
Pepsin - in stomach

Pancreatic enzymes - in small intestine.
What is the role of pepsin?
It begins the process of cleaving proteins into polypeptides, in the stomach.
What is an important pancreatic enzyme for protein digestion?
Trypsinogen - secreted into the duodenum.
What activates trypsinogen?
Enteropeptidase (from duodenum) cleaves trypsinogen -> trypsin
What does Trypsin do?
It's the active compound;cleaves polypeptides into Tri/Dipeptides and Amino acids.
Other than cleaving peptides what does trypsin do?
=cleaves trypsinogen (its inactive form)! autocatalysis
-activates OTHER proteases from the pancreas too.
Why does the pancreas secrete so many different proteases?
To cleave the different bonds in proteins - made up of many different amino acids.
Other than pancreatic enzymes, what cleaves proteins in the small intestine?
Epithelial enzymes in the duodenal wall.
What do epithelial enzymes chop proteins into?
Tri/dipeptides and Amino Acids (same as pancreatic enzymes)
What protein types can be absorbed, and what can't?
-Amino acids/Di/Tripeptides all can be absorbed
-Proteins cannot be absorbed.
What occurs when protein is absorbed in the small intestine?
Anaphylactic shock.
What results from anaphylactic shock?
Vasodilation and low blood pressure.
What 3 other materials are absorbed from the GI tract?
-Vitamin b12
How is Vit B12 absorbed?
by intrinsic factor released from parietal cells.
How does IF allow Vit B12 absorption?
1. IF binds Vit B12 = complex
2. Complex passes thru GI to ileum.
3. In ileum, receptor for complex takes up Vit B12 and IF goes away.
4. Vit B12 released into blood.
What is Vit B12 necessary for?
RBC production
What 2 proteins are needed to get calcium from the GI lumen across an enterocyte, to blood?
1. Ca2+ binding protein on the lumen side
2. Ca2+ ATPase on the blood side
What happens after Ca2+ crosses from the GI lumen into the enterocyte via the Ca binding protein?
It passes into the blood by primary active transport via Ca2+ ATPase.
What is Vit D3 and what is its function?
A steroid hormone that upregulates Ca2+ binding protein and Ca2+ ATPase
So what is the effect of Vit D3?
More absorption of Calcium from GI tract into bloodstream.
How do we get more Calcium?
By activating more Vit D3
How do we get more Activated Vit D3?
By parathyroid hormone - it causes the release of activated Vit D3 from the kidneys.
And what stimulates increased parathyroid hormone release?
decreased plasma calcium levels - so it's just a response to a need.
What's the pathway that increases calcium absorption?
1. Low plasma calcium
2. Increased parathyroid hormone
3. More active VitD3 from kidney
4. Increased Ca proteins in enterocytes
5. More absorption!
What is the oxidative state of iron when eaten? when absorbed?
Eaten as Ferric
Absorbed as Ferrous
What is the storage form of Iron?
What is ferritin without Fe?
When body iron levels are low, what happens to iron inside enterocytes?
Comes off ferritin and gets absorbed. Apoferritin increases
When body iron levels are high, what happens to iron inside enterocytes?
Don't need iron; more is stored or if its not needed, gets excreted in feces.