Gastric acid physiology

Question 1

What is anterior to the stomach?

Answer 1

Liver

Question 2

What is posterior to the stomach?

Answer 2

pancreas, colon, diaphragm, spleen

Question 3

What marks the caudal aspect of the gastric body?

Answer 3

Incisura angularis

Question 4

What is the fundus in contact with?

Answer 4

hemidiaphragm and the spleen

Question 5

What are the two types of gastric mucosa that you find in the stomach?

Answer 5

Oxyntic gland mucosa and pyloric gland mucosa. The oxyntic gland mucosa is prox 80% and secretes acid into the body and fundus.

The pyloric mucosa is in the antrum (20% of stomach). Here, GASTRIN is synthesized and released.

Question 6

Describe, very basically, the embryological formation of the stomach

Answer 6

1. Dilation of distal foregut
2. Dorsal aspect grows more rapidly=greater curvature
3. Stomach rotates 90 degrees clockwise

Question 7

What does the right vagus innervate?

Answer 7

posterior stomach wall (primordial right side)

Question 8

What does the left vagus innervate?

Answer 8

Anterior stomach wall (primordial left side)

Question 9

What are the five layers of the stomach?

Answer 9

1. Mucosa
2. Lamina Propria
3. Submucosa
4. Muscularis propria
5. Serosa

Question 10

What’s in the submucosa?

Answer 10

Connective tissue containing lymph, A/V, enteric plexus, plasma cells

Question 11

What is in the muscularis propria?

Answer 11

3 muscle layers: inner oblique, middle circular, and outer longitudinal

Question 12

What kinds of cells are in the neck?

Answer 12

parietal and mucous neck cells and PRECURSOR cells

Question 13

What kinds of cells are in the base?

Answer 13

Chief cells, Enterochromaffin Like Cells, G and D cells

Question 14

What do precursor cells do?

Answer 14

They migrate upwards < 1week to become surface mucous cells or downwards (>1 week) to become parietal or chief cells

Question 15

What are the motor fxns of the stomach?

Answer 15

Reservoir for food (Fundus/Body)
mixes, grinds food (antrum)
Empties slowly into duodenum (Pylorus)
Pepsinogen secretion

Question 16

What is significant about the cardia?

Answer 16

Trasition zone from squamous to columnar

Shallow gastric pits with more surface mucous cells

Question 17

What is significant about the antrum?

Answer 17

Regulates gastric secretion through Gastrin/Somatostatin

Question 18

What kind of gastric pits do you see in the fundus/body?

Answer 18

DEEP pits
Parietal, Chief cells mostly
Also ECL and D cells

Question 19

What kind of gastric pits cells do you see in the antrum?

Answer 19

INTERMEDIATE pits

Endocrine cells: G and D cells

Question 20

What are the secretions of the fundus and body?

Answer 20

H+
Intrinsic factor
Pepsinogens
Lipase

Question 21

What do chief cells secrete?

Answer 21

Pepsinogen and gastric lipase

Question 22

What happens in an individual parietal cell when it is stimulated?

Answer 22

Tubulovesicles with H/K ATPases attach to the canaliculus, which expands. The exchanger pumps H+ into the canaliculus which releases HCl into the lumen

Question 23

What stimulates the parietal cell?

Answer 23

Acetylcholine
Gastrin (works on ECL)
Histamine (increases cAMP intracellularly, required fro gastrin secretion)

Question 24

How does the parietal cell generate acid

Answer 24

H/K ATPase pumps H out, and K in.

• An open K channel allows K to “recycle” back in and out
• A Cl- pump maintains electroneutrality
• Carbonic anhydrase converts CO2+OH- into HCO3- which diffuses into the plasma

Question 25

What happens to the alkaline tide?

Answer 25

Bicarb is released interstitially to the surface epithelium to buffer the gastric mucosa

Question 26

At low secretion rates, what do you see in the gastric juices?

Answer 26

NaCl. Low Potassium and H+. Looks like interstitial fluid, with some bicarb present.

Question 27

At high secretion rates, what is the composition of gastric juices?

Answer 27

HCl. Levels of Potassium and sodium are low.

Question 28

Concentrations of what ions are higher in gastric juices than plasma?

Answer 28

H+, Cl, and K are higher. Na+ concentration is lower

Question 29

What are components of soluble mucus?

Answer 29

Mucin with disulfide bridges

Question 30

What is insoluble mucous?

Answer 30

Mucous secreted by surface mucous cells in response to physical or chemical stimuli

Question 31

What enhances soluble mucus secretion?

Answer 31

Acetylcholine from vagal nerve stimulation

Question 32

What are the endocrine hormones in gastric acid secretion?

Answer 32

Gastrin
CCK
Secretin
Glucose dependent insulinotropic peptide

Question 33

What disrupts the gastric mucosa?

Answer 33

aspirin, ethanol, NSAIDs, bile salts

Question 34

What are the hormones with paracrine secretion?

Answer 34

somatostatin and histamine

Question 35

What are the neurocrine hormones?

Answer 35

Ach and gastrin releasing peptide

Question 36

What stimulates gastrin release?

Answer 36

Amino acids
Stomach distention
Vagal stimulation by GRP

Question 37

What does gastrin do?

Answer 37

Stimulates acid secretion thru ECL or by releasing histamine which binds to parietal cells

• Directly stimulates parietal cells
• Stimulates mucosal growth
• Stimulates pepsinogen

Question 38

What inhibits gastrin?

Answer 38

LOW pH of stomach and somatostatin

Question 39

What are the phases of acid secretion?

Answer 39

1. Interdigestive (basal diurnal rhythm)
2. Cephalic (thru vagus)
3. Gastric (food in stomach, distention, peptides)
4. Intestinal (digestion products)

Question 40

What are the most important phases of acid secretion?

Answer 40

Gastric (50%)

Cephalic (30%)

Question 41

How does gastrin stimulate acid release by the parietal cell?

Answer 41

Directly

Indirectly by stimulating the ECL cell to release histamine

Question 42

What is an important stimulator in the intestinal phase?

Answer 42

Amino acids stimulate gastrin release

However, Chyme and other eneterogastrones inhibit acid secretion and gastric emptying (GIP, CCK, Secretin)