4. The Stomach

Question 1

What are the roles of the stomach?

Answer 1

Storage facility
Start digestion f protein
A little bit of carb and fat digestion
Disinfect

Question 2

What is the cardia of the stomach?

Answer 2

Opening of stomach from oesophagus

Question 3

What is the antrum of the stomach?

Answer 3

Bottom, narrower section of stomach

Question 4

What is the sphincter at the junction of stomach and duodenum?

Answer 4

Pyloric sphincter

Question 5

What sphincter is at the junction of the oesophagus and stomach?

Answer 5

Lower oesophageal sphincter

Question 6

What is the purpose of the right crus of diaphragm?

Answer 6

Close junction between oesophagus and stomach when intra abdominal pressure rises

Question 7

What helps to prevent reflux of stomach contents into the oesophagus?

Answer 7

Receptive relaxation
LOS
Right crus of diaphragm

Question 8

What is receptive relaxation?

Answer 8

Relaxation of proximal stomach muscles so that fundus distends, happens due to peristalsis of oesophagus

Question 9

What are the layers of muscles of the stomach?

Answer 9

Oblique
Circular
Longitudinal

Question 10

What is the epithelial surface of the stomach lined with?

Answer 10

• Surface mucous cells which secrete mucus, forms a layer between lumen of stomach and epithelial layer of stomach
• Gastric pits lead to gastric glands

Question 11

What is the purpose of gastric glands?

Answer 11

Contain parietal cells (produce acid), chief cells (secrete pepsinogen), enteroendocrine cells (G cells)

Question 12

What is pepsinogen?

Answer 12

Precursor to pepsin, activated by acid in stomach

Question 13

What do G cells secrete?

Answer 13

HCO3 (protective against acid to stomach wall)

Gastrin

Question 14

What protects the stomach wall form its acidic contents?

Answer 14

HCO3 - pH neutral layer
Prostaglandins - increase mucosal blood flow, support mucus layer, generally protective
Cells replaced regularly

Question 15

How does the parietal cell produce acid?

Answer 15

Exchanges intraluminal K+ for H+, using H+K+ ATPase/proton pump

Question 16

Where are the proton pumps in parietal cells located?

Answer 16

Within tubulovesicles

Question 17

What happens during the resting phase of the parietal cells?

Answer 17

No acid is secreted

Tubulovesicles are not in contact with the apical membrane

Question 18

How do the parietal cells move from the resting phase to the stimulated phase?

Answer 18

Apical membrane forms canaliculi with microvilli which then fuse with the tubulovesicles to allow secretions

Question 19

What stimulates acid production in the stomach?

Answer 19

Sensory triggers (30%)- smell, sight, taste
Gastric triggers (60%)- stretching of stomach, presence of amino acids and small peptides 
Intestinal triggers (10%)- chyme in duodenum, presence of partially digested proteins

Question 20

How can parietal cells be ‘turned on’?

Answer 20

Gastrin receptors - cholecystokinin
Histamine receptors - histamine onto H2 receptor
Muscarinic receptors - vagal stimulation

Question 21

How are G cells stimulates to produce gastrin?

Answer 21

Peptides in stomach lumen
Acetyl choline (vagal stimulation)
Gastrin releasing peptide (vagal stimulation)

Question 22

What produces histamine?

Answer 22

Entero-chromaffin like cell

Question 23

How is the entero-chromatin like cell stimulated?

Answer 23

Vagal stimulation

Gastrin on gastrin receptors

Question 24

What is the role of D cells?

Answer 24

‘Turn off’ parietal cells

Question 25

How do D cells work?

Answer 25

Lots of acid gives low pH, D cell detects this drop in pH
Once stimulated D cells produce somatostatin (inhibitory hormone), this inhibits G cells from secreting gastrin by a somatostatin receptor

Question 26

How do H+ and Cl- get to being released from the parietal cell?

Answer 26

In the cell, H2O and CO2 combine to form H2CO3 which then dissociates into H+ and HCO3- (catalysed by carbonic anhydrase)
HCO3-/Cl- transporter bringing Cl- into the cell
HCO3- enters venous blood leaving stomach and increases pH (alkaline tide)