7) Functions of the Stomach

Question 1

What are the basic functions of the stomach (4)?

Answer 1

Stores food
Disrupts food (contractions)
Continues digestion
Disinfects food

Question 2

What is the first section of the stomach called?

Answer 2

Cardia, where oesophagus enters

Question 3

What are the other sections of the stomach (top to bottom)?

Answer 3

Fundus, body, antrum, pylorus (+sphincter)

Question 4

What is the change in epithelium at the cardia?

Answer 4

Transition of stratified squamous to columnar (secretion)

Question 5

Describe the muscosa of the stomach:

Answer 5

In folds (rugae), to allow distension by flattening of these folds

Question 6

What are gastric pits?

Answer 6

‘Little holes’ on stomach surface

These pits have gastric glands (specialised cells) at the bottom

Question 7

What causes the movement of substances from the cardia to pylorus?

Answer 7

Upper stomach has basal tones created by sustained contractions which force flow down funnel shaped stomach

Question 8

How many muscle layers does the stomach have?

Answer 8

3 - oblique, circular and outer longitudinal

Question 9

What is receptive relaxation?

Answer 9

As food travels down oesophagus, vagus nerve triggers relaxation of orad stomach wall (flattening of rugae)

Question 10

What does receptive relaxation stop?

Answer 10

Stops rises in intra-gastric pressure

Prevents reflux

Question 11

What are the functions of stomach acid?

Answer 11

Helps unravel proteins - larger SA
Activates proteases - pepsin
Disinfection

Question 12

What do parietal cells secrete?

Answer 12

HCl

Intrinsic factor

Question 13

What do G cells secrete?

Answer 13

Gastrin

Question 14

What do enterochromaffin like cells secrete?

Answer 14

Histamine

Question 15

What do chief cells secrete?

Answer 15

Pepsinogen

Question 16

What do D cells secrete?

Answer 16

Somatostatin

Question 17

What do mucous cells (surface + neck) secret?

Answer 17

Mucus

Question 18

What are the predominant secretions of the cardia?

Answer 18

Mucus

Question 19

What are the main secretions of the fundus and body?

Answer 19

Mucus, HCl, pepsinogen

Question 20

What are the main secretions of the pylorus?

Answer 20

Gastrin, somatostatin

Question 21

What stimulates secretion of stomach acid?

Answer 21

Gastrin, histamine and ACh

Question 22

What feature of the parietal cell allows increased acid secretion?

Answer 22

Invaginations on cell surface (canaliculi) increase SA for secretion

Question 23

What stimulates gastrin secretion?

Answer 23

Peptides/AAs in the stomach lumen

Vagus stimulation - ACh, gastrin releasing peptide

Question 24

What inhibits acid production?

Answer 24

Low stomach pH - food acts as buffer
Low pH also activates D cells –> somatostatin which inhibits G and ECL cells
Reduction in stomach distension reduces vagal activity

Question 25

Describe the formation of HCl:

Answer 25

Water split to OH- and H+ H+ and Cl- into stomach lumen to form HCl Uses H+/K+ ATPase

Question 26

What happens to the OH- produced in HCl formation?

Answer 26

Combines with CO2 to form HCO3- | This moves into bloodstream, alkaline tide (HCO3-/Cl- antiporter)

Question 27

What are the 3 phases of digestion?

Answer 27

Cephalic Gastric Intestinal

Question 28

What occurs in the cephalic phase of digestion?

Answer 28

Vagus nerve stimulates parietal and G cells in response to smelling, tasting, chewing and swallowing Increase in gastric motility 30% of HCl

Question 29

What occurs in the gastric phase of digestion?

Answer 29

Distension of stomach stimulates vagus (parietal and G cells) Presence of AA/peptides stimulates G cells Food acts as buffer so no inhibition of gastrin Enteric NS and gastrin cause strong SM contractions

Question 30

What occurs in the intestinal phase of digestion?

Answer 30

Inhibition of G cells due to presence of lipids - enterogastric reflex, reduced vagal Chyme stimulates CCK and secretin

Question 31

What defences does stomach have against acid?

Answer 31

Mucus and HCO3- - form thick alkaline viscous layer over epithelium High turnover of epithelial cells Prostaglandins maintain mucosal blood flow

Question 32

What can breach stomach defences?

Answer 32

Alcohol - dissolves mucus layer Helicobacter pylori - inflamm of stomach lining NSAIDS - inhibit prostaglandins

Question 33

What can breach of stomach defence lead to?

Answer 33

Gastritis Ulceration Reflux disease

Question 34

What pharmacological interventions can be used to reduce acid secretion?

Answer 34

H2 blockers - cimetidine | Proton pump inhibitors - omeprazole

Question 35

What slows gastric emptying?

Answer 35

Fat, low pH and hypertonicity in duodenum