GI Physiology: Stomach

Question 1

Where does the major portion of digestion happen?

Answer 1

The beginning of the small intestine

Question 2

Digestion in the stomach involves primarily one macronutrient. Which one is it?

Answer 2

Protein!

Question 3

What does the acid do to proteins in the stomach?

Answer 3

Denatures them

Question 4

What are the three major functions of the stomach?

Answer 4

1. Motor
2. Secrete products
3. Secrete peptide hormones

Question 5

What is a function of the stomach that allows you to eat a lot without barfing?

Answer 5

It is highly compliant! It can take up ~2L without an increase in pressure.

Question 6

How does lipase and amylase work in the stomach despite being inactivated at low pH?

Answer 6

Since the food bolus that is swallowed is a ball, the enzymes stuck in the middle of the bolus are shielded from the stomach acid and continue to work a little.

Question 7

Food particles that are >1 mm in diameter are ____ out of the stomach when the stomach is empty.

Answer 7

swept

Question 8

Name six major things that are secreted in the stomach.

Answer 8

1. Pepsinogen
2. HCl
3. Mucus
4. Gastrin
5. Intrinsic factor
6. Water

Question 9

What are the three functions of acid in the stomach?

Answer 9

1. Convert pepsinogen to pepsin
2. Kills microbes
3. Denatures protein

Question 10

Intrinsic factor is necessary for absorption of _____.

Answer 10

B12

Question 11

How much water is secreted into the stomach per day?

Answer 11

2.5 L

Question 12

Where in the GI tract is B12 absorbed?

Answer 12

distal ileum

Question 13

What does gastrin do? What cells secrete it?

Answer 13

Stomach G cells secrete gastrin. It stimulates acid secretion by parietal cells, pepsinogen secretion by chief cells, and histamine secretion by ECL cells.

Question 14

Where are cells located that make somatostatin (3)? What does it do?

Answer 14

It is made by cells in the stomach, small intestine, and pancreas (delta cells). It inhibits gastrin release (cells in stomach), decreases endocrine and exocrine secretions (pancreas and liver) and decreases bile flow (liver).

Question 15

Where are cells located that make CCK? What does it do?

Answer 15

Made by cells in the small intestine. It acts on cells in the pancreas and gallbladder to increase muscle contractions and associated enzyme secretion.

Question 16

Where are cells located that make secretin? What does it do?

Answer 16

Made by cells in the duodenum. Acts on the pancreas and bile ducts to increase bicarbonate and fluid secretion.

Question 17

Where are cells located that make gastrin releasing peptide (GRP)? What does it do?

Answer 17

Made by cells in the vagal nerve endings. Acts in the stomach to increase gastrin release.

Question 18

Where are cells located that make gastric inhibitory peptide (GIP)? What does it do?

Answer 18

Made by cells in the duodenum and jejunum. Acts on pancreatic cells to decrease fluid absorption.

Question 19

Which GI “hormone” is not a true hormone? Why?

Answer 19

GRP is not a true hormone because it is neuroendocrine.

Question 20

Describe the general distribution of GI hormones (gastrin, CCK, secretin, GIP).

Answer 20

Gastrin is found in the antrum of the stomach as well as in the small intestine (tapers off distally) and the others are just found in the small intestine primarily.

Question 21

In what structure are chief cells, parietal cells, and ECL cells found primarily? Where are the mucus cells found?

Answer 21

Chief cells, parietal cells, and ECL cells are found in the gastric glands (deep).

Mucous cells are found closer to the lumen in the gastric pits.

Question 22

What cells make pepsinogen?

Answer 22

Chief cells in the stomach glands

Question 23

What do parietal cells make?

Answer 23

H+ and intrinsic factor

Question 24

Where does the majority of protein digestion occur in the GI tract?

Answer 24

Small intestine

Question 25

An important component of mucus is _______, a glycoprotein that forms a _____ when it is hydrated.

Answer 25

mucin; forms a gel when hydrated

Question 26

Do detergents like bile salts, weak acids like aspirin, alcohol, and NSAIDs disrupt the mucosal barrier of the somach?

Answer 26

Yeah

Question 27

30% of stomach ulcers are not caused by H. pylori, but rather by ______-type medications.

Answer 27

aspirin

Question 28

If the gastric mucosal barrier is damaged, the underlying epithelium can become denuded, allowing ___ to infiltrate and degranulate ______ cells, releasing ______ that increases vascular permeability resulting in flooding of the GI lumen with Na+, _______, and ______.

Answer 28

epithelium denuded --> H+ infiltrates --> mast cell degranulation ---> histamine increases vascular permeability --> Na+, blood, and fluid flood the lumen.

Question 29

Parietal cells use a _______ exchanger to pump protons into the stomach, therefore ____ (an ion) must be present in order for this to work.

Answer 29

H+/K+ exchanger (PeePee exchanger - proton/potassium), so K+ is needed

Question 30

What is the "alkaline tide?"

Answer 30

This refers to the high pH of blood in the venous end of the capillary bed supplying gastric epithelium due to release of bicarbonate as a byproduct of H+ synthesis by parietal cells (CO2 + H2O --> H2CO3 --> HCO3- + H+).

Question 31

Why should you eat a cracker when you get heartburn?

Answer 31

Food is a good buffer.

Question 32

Describe the regulation of gastric acid and pepsin secretion.

Answer 32

When pH is low (no food so lots of acid), D cells will make somatostatin, which inhibits G cells (they stop making gastrin). When pH is high (presence of food decreases acid in stomach), D cells stop making somatostatin so G cells can make gastrin. The gastrin gets into the circulation and acts on three cells: ECL cells, Chief cells, and Parietal cells: ECL cells are stimulated to make histamine, which in turn stimulates both chief and parietal cells. Chief cells are stimulated by gastrin to make pepsinogen. Parietal cells are stimulated to make acid.

Question 33

What do H2 blockers do?

Answer 33

Inhibit acid secretion in the stomach

Question 34

Can acetylcholine act on ECL, parietal, and chief cells to stimulate them?

Answer 34

Yeah

Question 35

Name three receptors present on a parietal cell that can stimulate the cell when the appropriate ligand is bound.

Answer 35

muscarinic (Ach), H2 (histamine), gastrin receptor

Question 36

The majority of acid secretion is in response to the _____ phase.

Answer 36

gastric

Question 37

What are the four phases of acid secretion?

Answer 37

1. Interdigestive 2. Cephalic 3. Gastric 4. Intestinal

Question 38

Describe how emptying of the stomach contents into the duodenum is regulated.

Answer 38

If H+ concentration gets high in the duodenum, it will leak out and loop back to tell the stomach that it needs to slow down (short reflex). H+ can also indirectly act by getting into the blood, stimulating secretin to tell the stomach to slow down.

Question 39

Aside from H+ in the duodenum, what three other things will slow gastric emptying into the duodenum?

Answer 39

1. Fats (FFA) 2. Proteins (AA) 3. HypERtonicity

Question 40

By what two mechanisms can the stomach delay emptying into the duodenum?

Answer 40

1. Decrease muscle contractions | 2. Pyloric sphincter stays shut

Question 41

_______ neutralizes acid in the duodenum.

Answer 41

Bicarbonate