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57 Cards in this Set
- Front
- Back
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What allows for amplified mucosal surface area?
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Cylinder intestine - has circular folds - have villi - have microvilli
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What is the purpose of amplified SA? how much is it amplified?
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600x; for increased absorption.
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Where does most absorption occur in the GI tract?
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In the duodenum in the small intestine.
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What are 4 exceptions to where absorption occurs?
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1. Asprin (stomach)
2. Alcohol (stomach) 3. Water (lg intestine) 4. Electrolytes (lg intest) |
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What are the types of carbs that are seen by the GI tract?
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1. Polysaccharides
2. Disaccharides 3. Monosaccharides |
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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 |
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What are Disaccs?
What are the 3 types? |
broken down poly's, into 2 simple sugars.
-Sucrose (table sugar) -Lactose (milk) -Maltose (starch) |
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What are the 3 monosaccs?
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Glucose Fructose and Galactose.
-The only carbs that can be absorbed. |
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Where does carb digestion begin, by what action?
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In the mouth via salivary amylase.
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What does amylase do?
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breaks poly into disaccs
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What happens to carbs in the stomach?
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nothing; salivary amylase is inactivated by stomach acid.
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What 2 enzymes act on carbs in the small intestine?
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1. Pancreatic amylase
2. Epithelial disacchaaridases |
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What do epithelial disaccidases do?
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break disaccs into monos.
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Where are epithelial disaccharidases located/
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in the cell membrane of epithel cells lining the GI tract in the small intestine. NOT secreted.
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How is Glucose absorbed from the duodenal lumen?
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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. |
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How does glucose move from the enterocyte to the blood?
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Via facilitated diffusion with a carrier molecule.
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What are the 3 types of lipids?
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1. Triglycerides (90%)
2. Cholesterol 3. Phospholipids |
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What is the structure of a tryglyceride?
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-Glycerol backbone
-Fatty acid tails -Cannot be absorbed |
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What digests tryglycerides into monoglycerides? How?
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Lipases; cleave off 2 fatty acids to form a monoglyc.
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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). |
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In what condition are fats absorbed from the GI lumen?
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As broken down micelles
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What 4 things come out of micelles after being broken down?
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1. Monoglycerides
2. Free fatty acids 3. Cholesterol 4. Fat soluble vitamins A/D/E |
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When and where are bile salts absorbed?
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LAST; in the ileum - not in the glob.
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What happens to the broken down micelle contents in enterocytes?
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They get repackaged into a glob with a lipoprotein coat, aka a chylomicron.
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How do chylomicrons exit enterocytes?
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via exocytosis.
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Where do chylomicrons go after exocytosis from enterocytes?
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NOT to the bloodstream; they get picked up by the lymphatic system, and THEN to the blood.
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What is a protein?
What are polypeptides? |
a long string of aa
shorter strings of aa |
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what are 3 types of peptides?
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1. polypeptides (>3 aa)
2. Tripeptides 3. Dipeptides |
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what enzymes break down proteins, and where?
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Pepsin - in stomach
Pancreatic enzymes - in small intestine. |
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What is the role of pepsin?
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It begins the process of cleaving proteins into polypeptides, in the stomach.
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What is an important pancreatic enzyme for protein digestion?
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Trypsinogen - secreted into the duodenum.
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What activates trypsinogen?
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Enteropeptidase (from duodenum) cleaves trypsinogen -> trypsin
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What does Trypsin do?
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It's the active compound;cleaves polypeptides into Tri/Dipeptides and Amino acids.
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Other than cleaving peptides what does trypsin do?
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=cleaves trypsinogen (its inactive form)! autocatalysis
-activates OTHER proteases from the pancreas too. |
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Why does the pancreas secrete so many different proteases?
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To cleave the different bonds in proteins - made up of many different amino acids.
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Other than pancreatic enzymes, what cleaves proteins in the small intestine?
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Epithelial enzymes in the duodenal wall.
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What do epithelial enzymes chop proteins into?
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Tri/dipeptides and Amino Acids (same as pancreatic enzymes)
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What protein types can be absorbed, and what can't?
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-Amino acids/Di/Tripeptides all can be absorbed
-Proteins cannot be absorbed. |
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What occurs when protein is absorbed in the small intestine?
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Anaphylactic shock.
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What results from anaphylactic shock?
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Vasodilation and low blood pressure.
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What 3 other materials are absorbed from the GI tract?
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-Vitamin b12
-calcium -iron |
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How is Vit B12 absorbed?
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by intrinsic factor released from parietal cells.
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How does IF allow Vit B12 absorption?
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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. |
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What is Vit B12 necessary for?
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RBC production
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What 2 proteins are needed to get calcium from the GI lumen across an enterocyte, to blood?
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1. Ca2+ binding protein on the lumen side
2. Ca2+ ATPase on the blood side |
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What happens after Ca2+ crosses from the GI lumen into the enterocyte via the Ca binding protein?
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It passes into the blood by primary active transport via Ca2+ ATPase.
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What is Vit D3 and what is its function?
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A steroid hormone that upregulates Ca2+ binding protein and Ca2+ ATPase
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So what is the effect of Vit D3?
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More absorption of Calcium from GI tract into bloodstream.
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How do we get more Calcium?
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By activating more Vit D3
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How do we get more Activated Vit D3?
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By parathyroid hormone - it causes the release of activated Vit D3 from the kidneys.
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And what stimulates increased parathyroid hormone release?
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decreased plasma calcium levels - so it's just a response to a need.
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What's the pathway that increases calcium absorption?
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1. Low plasma calcium
2. Increased parathyroid hormone 3. More active VitD3 from kidney 4. Increased Ca proteins in enterocytes 5. More absorption! |
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What is the oxidative state of iron when eaten? when absorbed?
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Eaten as Ferric
Absorbed as Ferrous |
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What is the storage form of Iron?
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Ferritin
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What is ferritin without Fe?
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Apoferritin.
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When body iron levels are low, what happens to iron inside enterocytes?
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Comes off ferritin and gets absorbed. Apoferritin increases
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When body iron levels are high, what happens to iron inside enterocytes?
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Don't need iron; more is stored or if its not needed, gets excreted in feces.
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