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20 Cards in this Set
- Front
- Back
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Where does most of absortpion occur?
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small intestine
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How much do surface specializations in the SI increase surface area?
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600x
circular folds - 3x villi - 10x microvilli - 20x |
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What makes up the brush border in the intestine?
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enzymes and mucous which line the wall of the intestine (on epithelial cells) - also called the "unstirred layer"
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What CHO are digested/absorbed at intestinal wall?
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1) starch (a-1,4; a-1,6)
2) sucrose 3) lactose *cellulose (b-1,4) is NOT digested by enzymes of the gut |
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What are the 3 main digestive enzymes in the small intestine?
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1) ptyalin: salivary amylase
(in center of bolus) 2) pancreatic amylase (does most of digestion - resuls in di- and tri-saccharides) 3) brush border enzyme (maltase, sucrase, and lactase - converts into monosaccharides) |
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What is the name of the transporter that brings glucose into mature epithelial cells of the small intestine?
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SGLT1 (Sodium-glucose linked transport protein 1)
- both Na+ and glucose are transported into cell |
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What transporter removes glucose from cell (across basolateral membrane of enterocyte)?
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GLUT2
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What does the overall absorption of glucose in the intestine depend on?
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Na+ transport out of the cell
(via basolateral membrane Na/K ATPase) |
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What is the difference between the carriers that glucose uses to enter and leave an enterocyte and those that galactose and fructose use?
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galactose: SGLT1 and GLUT2
(same as glucose) fructose: GLUT5 and GLUT2 (NOT Na+ linked, NOT interdependent) |
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When does absorption of glucose and galactose occur with respect to one another?
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glucose first, then galactose
(they are competing for the same carrier) |
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How much glucose has been absorbed by the time chyme reaches the jejunum?
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50%
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How much protein is digested and absorbed by gut/day?
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60 grams/day
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Name the 3 enzymes that help digest proteins.
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1) pepsin (from stomach)
2) proteolytic enzymes of pancreas (endopeptidases and exopeptidases) 3) brush border peptidases |
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What are the three sites of protein digestion in the small intestine?
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1) lumen (pepsin)
2) unstirred layer (bb peptidases) 3) enterocyte (cytoplasmic peptidases) |
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How are small peptides absorbed in the SI?
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- via carrier-mediated protein that carries H+ and peptide into cell and depends on a Na gradient
- once in cell bkdn into aas and diffuse across basolateral membrane |
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How are aas absorbed in the SI?
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- via membrane bound carriers coupled to Na (going down conc gradient)
- basic aas use Na-independent carriers *neutral aas can use either |
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Why is protein digestion delayed in the duodenum?
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because it is slow at onset and incomplete
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How does blood flow change after a meal (in the brachio-cephalic artery and SMA)?
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brachio-cephalic a. - decreases
SMA - flow increases * mediated by hormonal AND neural influences |
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Why does flow in the SMA increase after a meal?
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- need continuous flow of blood in gut to take nutrients away from villus so that the gradient is maintained
- deliver nutrient-rich blood to liver to store as glycogen (enhanced by GIP) |
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How does GIP work?
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glucose presence in duodenal lumen - GIP released into blood - pancreatic endocrine cells secrete insulin - increase uptake of glucose from blood (less of a rise in blood glucose after a meal)
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