Block VIII - Digestive

Question 1

What is the major function of gastrointestinal system?

Answer 1

To digest and absorb nutrients

Question 2

What is the effect of histamine on acid secretion in the stomach?

Answer 2

Increases acid secretion

Question 3

In parietal cells, what processes mediate HCl secretion?

Answer 3

H and C; are secreted separately via two different pathways. H is generated from water and CO2 in parietal cells with the help of carbonic anhydrase, and secreted by H/K ATPase pump in lumen. Cl transferred into the cell by basolateral HCO3/Cl exchanger, exit into lumen via Cl channel

Question 4

In the stomach, H ions are secreted in exchange for what?

Answer 4

K

Question 5

What is secretin?

Answer 5

Secretin is a hormone secreted by the endocrine cells of the small intestine, it stimulates the pancreas to release bicarbonate ions

Question 6

What is the advantage of enzymatic hydrolysis?

Answer 6

Enzymatic hydrolysis is faster than hydrolysis without an enzyme

Question 7

Cholecystokinin is released in what cells in the presence of fats?

Answer 7

The duodenal mucosal cells

Question 8

What is the role of bile salts in digestion?

Answer 8

Emulsifying agnets for large fat droplets in the upper intestinal tract

Question 9

In what form are dietary carbohydrates absorbed in the small intestine?

Answer 9

Monosaccharides (note: sucrose and lactose are disaccharides)

Question 10

Where do dietary carbohydrates go after absorption?

Answer 10

The are transported to the liver via the hepatic portal vein after breakdown to simple monosaccharides

Question 11

What is required for efficient absorption of fats in the alimentary tract?

Answer 11

The presence of pancreatic lipase

Question 12

Is the polysaccharide cellulose digested in the body?

Answer 12

Yes, it is partially digested by bacteria in the colon. However cellulose cannot be digested by small intestinal enzymes

Question 13

Where are the products of digestion absorbed?

Answer 13

The products of digestion are absorbed across the intestinal epithelial cells

Question 14

In what form is dietary lipid absorbed by the SI transported in the lymph?

Answer 14

Chylomicrons

Question 15

What are the stimuli for GI reflex?

Answer 15

Distension of the wall by the volume of the luminal contents, increase in chyme concentration of specific digestion products, increase of chyme osmolarity, increase of chyme acidity

Question 16

What cells does the submucosal plexus directly act on?

Answer 16

Endocrine and secretory cells

Question 17

Is GI activity regulated by short and long neural reflexes?

Answer 17

Yes

Question 18

If enteric nervous system is a part of autonomic nervous system, do they use epi, norepi, and ach as their transmitters only?

Answer 18

No. Enteric nervous system is similar to CNS, using as much as 30 different neurotransmitters

Question 19

What is secreted by gastric chief cells?

Answer 19

Pepsinogen

Question 20

What volume of fluid is secreted daily into the GI tract?

Answer 20

7000 ml

Question 21

Where do water and electrolytes absorbed in the GI tract?

Answer 21

SI

Question 22

Where are exocrine and endocrine cells located in the GI tract?

Answer 22

The epithelial layer

Question 23

What is the advantage of the existence of proenzymes for pancreatic enzymes?

Answer 23

To facilitate safe storage

Question 24

What is the function of microvilli in the SI?

Answer 24

Greatly increase SA for absorption of nutrients

Question 25

What are the substances/condition that stimulates acid secretion in the stomach?

Answer 25

Gastrin, histamine, acetylcholine, distension of the stomach

Question 26

Where is gastrin secreted?

Answer 26

Antrum of the stomach

Question 27

What do micelles consist of?

Answer 27

Bile salts, fatty acids, phospholipids, 2-monoglycerides

Question 28

Is vitamin B12 a water-soluble vitamin?

Answer 28

Yes, it binds to the intrinsic factor (IF) which is secreted by the parietal cells of the stomach. The IF-vitamin B12 is absorbed by endocytosis at ileum

Question 29

What is the size of micelles?

Answer 29

3-10 nm

Question 30

Do bile salts directly hydrolyze lipids?

Answer 30

No, bile salts facilitate digestion and absorption of lipids but do not themselves digest

Question 31

What is the function of pancreatic lipase?

Answer 31

Pancreatic lipase is specific to hydrolyze triglycerides

Question 32

Which enzyme converts oligopeptides into individual amino acids?

Answer 32

Caboxypeptidases A and B

Question 33

What is the process of secondary active transport of glucose?

Answer 33

ATP is hydrolyzed by the basolateral Na-K ATPase for active transport of Na across the basolateral membrane into the interstitial fluid. The Na gradient provides the energy for glucose entry carried by glucose transporter (SGLUT-1) at the brush border

Question 34

What mechanisms by which Na can be absorbed in intestinal epithelial cells?

Answer 34

Na enter the cells from the apical membrane by Na/Cl co-transport and Na/H exchanger, Na channels, co-transported with amino acids or monosaccharide. Sodium exits the cells at basolateral membrane by Na/K ATPase

Question 35

What is the effect of sympathetic stimulation on the digestive process?

Answer 35

Decrease the intestinal motility

Question 36

Is bile salt recycling?

Answer 36

Yes about 90% of excreted bile salts are reabsorbed by secondary active transport of the ileum

Question 37

What is membrane digestion?

Answer 37

Membrane digestion is carried out at the external surface of the membrane of microvilli by the enteric and absorbed enzymes. Therefore the final stages of digestion are integrated and the initial stages of transport begin. Brush-border oligosaccharidases break oligosaccharides into onosaccharides (fructose, glucose, galactose)

Question 38

Are small peptides (bipeptides, tripeptides) absorbed in SI?

Answer 38

Yes, intestinal enterocytes contain special transporters to take up amino acids and small peptides