GI: 346 - 348

Question 1

Which cells make intrinsic factor?

Answer 1

Parietal cells (stomach)

Question 2

What is the main role of intrinsic factor?

Answer 2

Binding protein for B12

Question 3

Where is B12 taken up?

Answer 3

Terminal ileum

Question 4

What happens as a result of autoimmune destruction of parietal cells?

Answer 4

Chronic gastritis and pernicious anemia

Question 5

Which cells produce gastric acid?

Answer 5

Parietal cells (stomach)

Question 6

What is the main effect of gastric acid?

Answer 6

Decrease stomach pH

Question 7

How is gastric acid regulated?

Answer 7

Increased by: histamine, ACh, gastrin

Decreased by: somatostatin, GIP, prostaglandin, secretin

Question 8

What is a gastrinoma?

Answer 8

Gastrin-secreting tumor that causes high levels of acid secretion and ulcers refractory to medical therapy

Question 9

Which cells produce pepsin?

Answer 9

Chief cells (stomach)

Question 10

What is the main action of pepsin?

Answer 10

Protein digestion

Question 11

How is pepsin regulated?

Answer 11

Increased by vagal stimulation and local acid

Question 12

What is the inactive form of pepsin and how is it activated?

Answer 12

Pepsinogen, activated by H+

Question 13

Which cells in the GI tract secrete HCO3-?

Answer 13

Mucosal cells (stomach, duodenum, salivary glands, pancreas) and Brunner glands (duodenum)

Question 14

What is the main function of HCO3- in the GI tract?

Answer 14

Neutralizes acid

Question 15

How is HCO3- regulated in the GI tract?

Answer 15

Increased by pancreatic and biliary secretion with secretin

Question 16

Where do you find the HCO3-containing mucus?

Answer 16

Covers the gastric epithelium

Question 17

What are the 3 secretory cells found in the duodenum?

Answer 17

I cells (CCK), S cells (secretin), and K cells (GIP)

Question 18

What are 3 secretory cells found in the antrum?

Answer 18

D cells (somatostatin), mucous cells, G cells (GRP)

Question 19

In which part of the stomach will you find parietal cells and chief cells?

Answer 19

Body

Question 20

What is the main mechanism by which gastrin promotes acid secretion?

Answer 20

Exerts effects on enterochromaffin-like (ECL) cells leading to histamine release rather than through its direct effect on parietal cells

Histamine goes on to increase intracellular levels of cAMP in the parietal cell –> drives H-K ATPase

Question 21

Does atropine completely block vagal stimulation of gastrin release? Why or why not?

Answer 21

No, it blocks parietal cells but does not affect vagal stimulation of G cells since G cells use GRP instead of ACh

Question 22

What does ACh bind on the gastric parietal cell?

Answer 22

M3 receptor

Question 23

What does histamine bind on the gastric parietal cell?

Answer 23

H2 receptor

Question 24

What does gastrin bind on the gastric parietal cell?

Answer 24

CCK-B receptor

Question 25

What are two enzymes/compounds that antagonize the effects of ACh, gastrin, and histamine in the parietal cell?

Answer 25

1. Prostaglandins/misopristol | 2. Somatostatin

Question 26

How do prostaglandins/misopristol and somatostatin exert their action on the parietal cell?

Answer 26

Via Gi protein to decrease the levels of cAMP

Question 27

What class of drugs can inhibit release of H+ from parietal cells?

Answer 27

Proton pump inhibitors

Question 28

Where are Brunner glands located?

Answer 28

Duodenal submucosa

Question 29

What is the main function of Brunner glands?

Answer 29

Secrete alkaline mucus

Question 30

What happens to Brunner glands in peptic ulcer disease?

Answer 30

Hypertrophy

Question 31

Describe the tonicity/content of pancreatic secretions relative to the flow rate.

Answer 31

Isotonic fluid At low flow: high Cl At high flow: high HCO3

Question 32

What are 4 enzymes that are secreted by the pancreas?

Answer 32

1. Alpha amylase 2. Lipase, phospholipase A, colipase 3. Proteases 4. Trypsinogen

Question 33

What is the main role of alpha-amylase?

Answer 33

Starch digestion

Question 34

Which pancreatic enzymes are important for fat digestion?

Answer 34

Lipase, phospholipase A, colipase

Question 35

Give 4 examples of proteases secreted by the pancreas?

Answer 35

1. Trypsin 2. Chymotrypsin 3. Elastase 4. Carboxypeptidases

Question 36

What form are pancreatic proteases secreted as?

Answer 36

Zymogens (proenzymes)

Question 37

Describe the role of trypsinogen.

Answer 37

Once it is converted to its active form (trypsin) it can activate all of the other proenzymes and also cleave additional trypsinogen molecules into active trypsin (positive feedback loop).

Question 38

How is trypsinogen initially converted to trypsin?

Answer 38

By enterokinase/enteropeptidase, a brush-border enzyme on the duodenal and jejunal mucosa

Question 39

What is the only form of carbohydrate that can be absorbed by enterocytes?

Answer 39

Monosaccharides (glucose, galactose, fructose)

Question 40

Describe the absorption of glucose, galactose, and fructose.

Answer 40

Glucose, galactose - taken up by SGLT1 (Na+ dependent) Fructose - taken up by facilitated diffusion by GLUT5 All are transported to blood by GLUT2

Question 41

What is the D-xylose absorption test used for?

Answer 41

Distinguishes GI mucosal damage from other causes of malabsorption

Question 42

Where is iron absorbed and in what form?

Answer 42

Fe2+ in duodenum

Question 43

Where is folate absorbed?

Answer 43

Jejunum and ileum

Question 44

Where is B12 absorbed?

Answer 44

Terminal ileum along with bile acids (requires intrinsic factor)

Question 45

What are Peyer patches and where are they found?

Answer 45

Unencapsulated lymphoid tissue found in lamina propria and submucosa of ileum

Question 46

Which cells are found in Peyer patches?

Answer 46

1. M cells - sample and present antigens to immune cells | 2. B cells - stimulated in germinal centers differentiate into IgA secreting plasma cells

Question 47

What happens to the B cells that become IgA secreting plasma cells?

Answer 47

Reside in the lamina propria

Question 48

How is the IgA processed?

Answer 48

Receives protective secretory component and is then transported across epithelium to the gut to deal with intraluminal antigen

Question 49

What are the components of bile?

Answer 49

1. Bile salts 2. Phospholipids 3. Cholesterol 4. Bilirubin 5. Water 6. Irons

Question 50

Which enzyme catalyzes the rate-limiting step of bile synthesis?

Answer 50

Cholesterol 7alpha-hydroxylase

Question 51

What are bile salts?

Answer 51

Bile acids conjugated to glycine or taurine to make them water soluble

Question 52

What are 3 functions of bile?

Answer 52

1. Digestion and absorption of lipids and fat-soluble vitamins 2. Cholesterol excretion (body's only means of eliminating cholesterol) 3. Antimicrobial activity (via membrane disruption)