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20 Cards in this Set

  • Front
  • Back
Where does most of absortpion occur?
small intestine
How much do surface specializations in the SI increase surface area?

circular folds - 3x
villi - 10x
microvilli - 20x
What makes up the brush border in the intestine?
enzymes and mucous which line the wall of the intestine (on epithelial cells) - also called the "unstirred layer"
What CHO are digested/absorbed at intestinal wall?
1) starch (a-1,4; a-1,6)
2) sucrose
3) lactose

*cellulose (b-1,4) is NOT digested by enzymes of the gut
What are the 3 main digestive enzymes in the small intestine?
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)
What is the name of the transporter that brings glucose into mature epithelial cells of the small intestine?
SGLT1 (Sodium-glucose linked transport protein 1)

- both Na+ and glucose are transported into cell
What transporter removes glucose from cell (across basolateral membrane of enterocyte)?
What does the overall absorption of glucose in the intestine depend on?
Na+ transport out of the cell

(via basolateral membrane Na/K ATPase)
What is the difference between the carriers that glucose uses to enter and leave an enterocyte and those that galactose and fructose use?
galactose: SGLT1 and GLUT2
(same as glucose)
fructose: GLUT5 and GLUT2
(NOT Na+ linked, NOT interdependent)
When does absorption of glucose and galactose occur with respect to one another?
glucose first, then galactose
(they are competing for the same carrier)
How much glucose has been absorbed by the time chyme reaches the jejunum?
How much protein is digested and absorbed by gut/day?
60 grams/day
Name the 3 enzymes that help digest proteins.
1) pepsin (from stomach)
2) proteolytic enzymes of pancreas (endopeptidases and exopeptidases)
3) brush border peptidases
What are the three sites of protein digestion in the small intestine?
1) lumen (pepsin)
2) unstirred layer (bb peptidases)
3) enterocyte (cytoplasmic peptidases)
How are small peptides absorbed in the SI?
- 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
How are aas absorbed in the SI?
- via membrane bound carriers coupled to Na (going down conc gradient)
- basic aas use Na-independent carriers
*neutral aas can use either
Why is protein digestion delayed in the duodenum?
because it is slow at onset and incomplete
How does blood flow change after a meal (in the brachio-cephalic artery and SMA)?
brachio-cephalic a. - decreases
SMA - flow increases

* mediated by hormonal AND neural influences
Why does flow in the SMA increase after a meal?
- 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)
How does GIP work?
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)