Exam #5: Gastric Secretions

Question 1

What are the secretory products of parietal cells? Where are these cells located?

Answer 1

Parietal cells secrete HCl & Intrinsic Factor

• HCl functions in protein digestion, sterilization, nutrient absorption
• Intrinsic Factor= Vitamin B absorption

**Parietal cells are located in the body of the stomach

Question 2

What is the secretory product of chief cells? Where are these cells located?

Answer 2

Chief cells secrete pepsinogen, which functions in protein digestion

*****Chief cells are located in BOTH the body & antrum of the stomach

Question 3

What are ECL cells? Where are these cells located? What is their product?

Answer 3

ECL, or “enterochromaffin-like” cells produce histamine, which promotes HCl secretion

*****ECL cells are located in the body of the stomach

Question 4

What is the secretory product of G-cells? Where are these cells located?

Answer 4

G-cells produce gastrin, which promotes HCl secretion

Question 5

What is the secretory product of D-cells? Where are these cells located?

Answer 5

D-cells produce somatostatin, which suppress HCl secretion

*****antrum of the stomach

Question 6

What is the secretory product of superficial epithelial/ neck cells? Where are these cells located?

Answer 6

Mucous
Bicarbonate

*****Both are gastroprotective & cells are located throughout the entire stomach

Question 7

How do neuronal pathways regulate acid secretion in the stomach?

Answer 7

ACh secretion

- promotion of mucous, bicarbonate, and HCl secretion

Question 8

How do paracrine pathways regulate acid secretion in the stomach?

Answer 8

Histamine binding to receptors on parietal cells stimulates acid secretion

Question 9

How do endocrine pathways regulate acid secretion in the stomach?

Answer 9

Gastrin binding to receptors on parietal cells stimulate acid secretion

Question 10

What are the functions of gastric acid?

Answer 10

1) Protein digestion & conversion of pepsinogen to pepsin (for protein digestion)
2) Provide sterile environment
3) Prevent bacteria and fungal growth
4) Facilitate absorption
5) Promote bile and enzyme flow

Question 11

What are the positive and negative regulators of gastric acid secretions?

Answer 11

Positive=

• ACh (neural)
• Histamine (ECL)
• Gastrin (G-cells)

Negative=
- Somatostatin (D-cells)

Question 12

What cells release the positive regulators of gastric acid secretion?

Answer 12

Histamine= ECL
Gastrin= G
Neural= ACh

Question 13

What cells release the negative regulators of gastric acid secretion?

Answer 13

D-cell secretion of somatostatin

Prostaglandins

Question 14

Describe the steps of how pepsinogen is converted in lumen of the stomach to the active protease pepsin.

Answer 14

• Pepsinogen is secreted by chief cells in the body & antrum of the stomach.
• HCl converts pepsinogen into pepsin (active) i.e. lower pH
• This is protective and ensure that pepsinogen is activated once it is in the lumen of the stomach
• Higher pH inactivates the enzyme

*****ACh is a key stimulus in the secretion of pepsinogen

Question 15

What is the site of intrinsic factor secretion?

Answer 15

Parietal cells secrete intrinsic factor in the body of the stomach

I.e. damage to parietal cells & the gastric epithelium will result in an inability to absorb Vitamin B12

Question 16

What is the physiological role of intrinsic factor?

Answer 16

• Complexes with Vitamin B12 in duodenum
• IF + Vitamin B12= absorbed in ileum via receptor mediated endocytosis

No IF= No Vitamin B12 absorption

Question 17

What are the two key stimuli for mucus secretion by epithelial and neck cells of the stomach?

Answer 17

There are two key regulators

1) ACh (neurocrine)
2) Prostaglandins (paracrine)

**Note that prostaglandins: 1) increase mucus & bicarbonate secretion, 2) suppression of HCl secretion, and 3) increased gastric blood flow

Question 18

What is the the physiological role of mucus in the stomach?

Answer 18

Gastroprotection; mucus creates a protective layer over the mucosal epithelium

Question 19

What are the components of mucus?

Answer 19

Mucin 
Bicarboante 
Phospholipids 
Electrolytes 
Water

Question 20

Outline the pathophysiology of gastritis.

Answer 20

Gastritis= inflammation of gastric mucosa caused by damage to the protective mucosal barrier–this inflammation DOES NOT NECESSARILY produce a break in the mucosal lining. Commonly caused by:

1) H. pylori
2) NSAIDs i.e. ASA

Question 21

Outline the pathophysiology of H. pylori infection.

Answer 21

• Urease creates a buffered microenvironment that is hospitalble to H. pylori colonization
• Colonization and subsequent immune response cause the mucosal damage that leads to ulceration

Question 22

Outline the pathophysiology of peptic ulcers.

Answer 22

Break in the protective lining of the lower esophagus, stomach, or duodenum

Question 23

Outline the pathophysiology of Zollinger-Ellison Syndrome.

Answer 23

Gastrin secreting tumor that results in high acid levels

Question 24

What are the four different phases of gastric acid secretion?

Answer 24

1) Interdigestive
2) Cephalic= sight or smell of food triggers vagal response to increase acid secretion

3) Gastric= stomach distention & presence of proteins causes vagal response to increase acid secretion
- Most gastric acid secreted in this phase

4) Intestinal= proteins in the duodenum causes acid secretion

Question 25

How are the four phases of gastric acid secretion regulated?

Answer 25

1) Interdigestive
2) Cephalic
3) Gastric= if pH falls below 1, feedback on D-cells to secrete somatostatin
4) Intestinal= peptides induce gastrin secretion

Question 26

Outline the mechanism of HCl production. What cells produce HCl?

Answer 26

Parietal cells secrete HCl i.e. gastric acid via a H+-K+ ATPase, or “proton pump”
- Located on the apical membrane of parietal cells

Question 27

What regulates the H+-K+ ATPase?

Answer 27

Stimulation

• Gastrin= direct increase or stimulation of histamine for indirect increase in H+/K+ ATPase pump
• ACh= like Gastrin, direct increase or stimulation of histamine for indirect increase in H+/K+ ATPase pump

Inhibition

• Prostaglandins= direct inhibition
• Somatostatin= indirect inhibition by decrease Gastrin & Histamine