GI - Physiology (GI Secretions)

Question 1

What are 4 GI secretory products?

Answer 1

(1) Intrinsic factor (2) Gastric acid (3) Pepsin (4) HCO3-

Question 2

What cells are the source of Intrinsic factor, and in what part of the GI system are they located?

Answer 2

Parietal cells (stomach)

Question 3

What cells are the source of gastric acid, and in what part of the GI system are they located?

Answer 3

Parietal cells (stomach)

Question 4

What 2 secretory products do parietal cells produce? Where are they located?

Answer 4

(1) Intrinsic factor (2) Gastric acid; Parietal cells (stomach)

Question 5

What cells are the source of Pepsin, and in what part of the GI system are they located?

Answer 5

Chief cells (stomach)

Question 6

What cells are the source of HCO3-, and in what part of the GI system are they located?

Answer 6

(1) Mucosal cells (stomach, duodenum, salivary glands, pancreas) and (2) Brunner glands (duodenum)

Question 7

What is the action of Intrinsic factor?

Answer 7

Vitamin B12-binding protein (required for B12 uptake in terminal ileum)

Question 8

What 2 conditions can be caused by autoimmune destruction of parietal cells?

Answer 8

Autoimmune destruction of parietal cells –> chronic gastritis and pernicious anemia

Question 9

What is the action of Gastric acid?

Answer 9

Decreases stomach pH

Question 10

What factors regulate Gastric acid production, and in what ways?

Answer 10

INCREASE: by histamine, ACh, gastrin; DECREASE: by somatostatin, GIP, prostaglandin, secretin

Question 11

What is a Gastrinoma? What physiological and medical consequences does it have?

Answer 11

Gastrinoma: gastrin-secreting tumor that causes high levels of acid secretion and ulcers refractory to medical therpay

Question 12

What is the action of Pepsin?

Answer 12

Protein digestion

Question 13

What factors regulate Pepsin, and in what way?

Answer 13

INCREASED by vagal stimulation, local acid

Question 14

What is the precursor for Pepsin, and how is it activated?

Answer 14

Inactive pepsinogen –> pepsin by H+

Question 15

What is the function of HCO3- in the GI system?

Answer 15

Neutralizes acid

Question 16

What factors regulate HCO3- secretion in the GI system, and in what way?

Answer 16

INCREASED by pancreatic and biliary secretion with secretin

Question 17

Where is HCO3- trapped in the GI tract?

Answer 17

HCO3- is trapped in mucus that covers the gastric epithelium

Question 18

On what site does gastrin act mostly, and what effects does this have?

Answer 18

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

Question 19

What is the action of Atropine on GI secretion? What is major regulatory factor of GI secretion is unaffected, and why?

Answer 19

Atropine blocks vagal stimulation of parietal cells. Vagal stimulation of G cells is unaffected, as a different transmitter (gastrin-releasing peptide, or GRP) is used, not ACh

Question 20

What are 3 GI secretory cells below the pyloric sphincter and their products?

Answer 20

(1) I cells - CCK (2) S cells - Secretin (3) K cells - GIP

Question 21

What are 3 GI secretory cells in the antrum of the stomach and their products?

Answer 21

(1) D cells - Somatostatin (2) Mucous cells - Mucus (3) G cells - Gastrin

Question 22

What are 3 GI secretory cells in the body of the stomach and their products?

Answer 22

(1) Parietal cells - HCl, Intrinsic factor (2) ECL cells - Histamine (3) Chief cells - Pepsinogen

Question 23

What are 3 stimulators of gastric parietal cells & their mechanisms? What is the most important mechanism of gastric parietal cell stimulation?

Answer 23

(1) ACh - ACh from vagus, signals through M3 receptor and Gq to promote H/K pump (2) Gastrin - G cells activated by GRP from Vagus to release gastrin, which signals through CCK receptor and Gq to promote H/K pump (3) Histamine - Gastrin from from G cells stimulates ECL cells (most important mechanism) to release histamine, which signals through H2 receptors and Gs to promote H/K pump

Question 24

What are 2 inhibitors of the gastric parietal cell gastric acid secretion? What is their mechanism?

Answer 24

(1) Prostaglandins/Misoprostol (2) Somatostatin; Signal through Gi to inhibit H/K pump

Question 25

What is considered to be the "alkaline tide" of a gastric parietal cell? Draw the explanation.

Answer 25

See p. 347 in First Aid 2014 for visual at top of page

Question 26

Draw the relation of carbonic anhydrase to the H/K pump in gastric parietal cells.

Answer 26

See p. 347 in First Aid 2014 for visual at top of page

Question 27

Where are Brunner glands located? What function do they serve?

Answer 27

Located in duodenal submucosa. Secrete alkaline mucus.

Question 28

In what condition is hypertrophy of Brunner glands seen?

Answer 28

Hypertrophy seen in peptic ulcer disease

Question 29

What tonicity does pancreatic secretion fluid have?

Answer 29

Isotonic fluid

Question 30

How does the flow rate of pancreatic secretions relate to change in ion concentrations?

Answer 30

Low flow => High Cl-; High flow => High HCO3-

Question 31

What are 4 kinds of pancreatic secretions?

Answer 31

(1) Alpha-amylase (2) Lipase, phospholipase A, colipase (3) Proteases (4) Trypsinogen

Question 32

What is the role of alpha-amylase? In what form is it secreted?

Answer 32

Starch digestion; Secreted in active form

Question 33

What is the role of lipase? What are the specific names of 2 other enzymes in pancreatic secretions that share this role?

Answer 33

Fat digestion; Lipase, Phospholipase A, Colipase

Question 34

What is the role of Proteases? In what form are they secreted?

Answer 34

Protein digestion; Secreted as proenzymes also known as zymogens

Question 35

What are 4 examples of Proteases?

Answer 35

Includes (1) trypsin, (2) chymotrypsin, (3) elastase, (4) carboxypeptidases

Question 36

To what is trypsinogen converted? What role(s) does this product play?

Answer 36

Converted to active enzyme trypsin => Activation of other proenzymes and cleaving of additional trypsinogen molecules into active trypsin (positive feedback loop)

Question 37

What enzyme converts trypsinogen to trypsin? Where is this enzyme found?

Answer 37

Trypsinogen converted to trypsin by Enterokinase/Enteropeptidase, a brush-border enzyme on the duodenal and jejunal mucosa