Week 4 Stomach

Question 1

describe the basic functions of the stomach?

Answer 1

receive food
store food
disrupt food
continue digestion- disinfect

Question 2

describe the patterns of motility of the stomach- receptive relaxation

Answer 2

we receive food faster than can digest so have receptive relaxation- vagally stimulated relaxation of orad stomach (proximal bit) which increases in size

• stops regurgitation as stops increasing pressure in the stomach
• gastric mucosal folds (rugae) allow distension

Question 3

what are the 3 main regions of the stomach and the 2 sphincters called?

Answer 3

fudus, body and antrum

lower oesophageal and pyloric sphincter

Question 4

describe the patterns of motility of the stomach- peristalsis

Answer 4

peristalsis mixes stomach contents in antrum disrupting the food

• coordinated movement- contractions every 20secs- proximal to distal–> as proximal larger and distal smaller contents are accelerated towards duodenum- as pyloric sphincter present prevents bigger contents being left behind and circulated again
• liquid chyme ejected into duodenum 3x per minute

Question 5

list the 6 man cell types and what they secrete in the stomach?

Answer 5

parietal cell (proximal stomach)- HCL (stomach acid) and intrinsic factor (vit b12)
G cell (antrum)- gastrin
D cell- somatostatin -ve feedback
ECL cells- histamine
chief cells- pepsinogen
mucus cells- mucus -protects surface

Question 6

what does the stomach secrete and from where?

Answer 6

mucus (surface mucous cells and mucous neck cels)/HCO3- - protects from acid
intrinsic factor ,HCL (parietal cells)
pepsinogen- pepsin (chief cells)

in order from surface to lower

Question 7

what is the difference between the gastric pit and gastric gland?

Answer 7

gastric pit- superficial element- pin prick holes in stomach lining
gastric gland- underneath with cells in

Question 8

how does acid help to continue digestion?

Answer 8

helps unravel proteins- activates proteases- pepsinogen->pepsin
disinfects stomach contents

Question 9

explain the mechanisms of gastrin secretion in the stomach

Answer 9

G cells in antrum- thick muscle part
stimulated by:
- peptides/AAs in lumen of stomach
- vagal nerve stimulation- Ach, Gastrin- releasing peptide (GRP)

Question 10

explain the mechanisms of secretions of HCL in the stomach and what fine tunes this?

Answer 10

HCL released from parietal cells- H+ pump
stimulated by:
- Ach from vagus nerve- responds to stretch of stomach
- Gastrin from G cells
- histamine from ECL cells

synergistic effect of more than one stimulating- histamine has fine tuning affect of acid production

Question 11

explain how acid secretion by the stomach is controlled

Answer 11

inhibition of G cells

• when food leaves the stomach pH drops as food buffers the acid–> low pH activates D cells which release somatostatin–> inhibits G cells and ECL cells(histamine)
• stomach distension reduces so vagal activity reduced

Question 11

how is stomach acid produced starting with H20?

Answer 11

water splits into OH- and H+
H+ moved into stomach lumen by H/K ATPase pump REQUIRES ENERGY
Cl moved into stomach lumen creating HCL (Cl exchanged for HCO3-)
K moved back out by channel protein

OH- combines with CO2 to form HCO3- which is moved into the blood stream via above exchanger- why blood pH rises after meal

Question 12

what is the alkaline tide?

Answer 12

HCO3- entering blood after a meal slightly increases pH

Question 13

what is the alkaline tide?

Answer 13

HCO3- entering blood after a meal slightly increases pH

Question 14

what is involved in cephalic digestion and what percentage of acid production does this account for?

Answer 14

cephalic 30%

• smell, taste, chewing, swallowing
• stimulates vagal nerve- parietal cells (H) and G cells (gastrin via GRP)

Question 15

what is involved in gastric digestion and what percentage of acid production does this account for?

Answer 15

gastric 60%

• distension of stomach -stimulates vagal nerve- parietal and G cells
• AAs and small peptides in stomach- stimulates G cells
• food buffers acid in stomach- why gastrin not inhibited

Question 16

what is involved in intestinal digestion and what percentage of acid production does this account for?

Answer 16

10%

• short phase quickly stopped by G cell inhibition via somatostatin
• chyme initially stimulates gastrin secretion

Question 17

describe the functions of the 3 stomach defences

Answer 17

1. mucous- released by surface mucous and neck cells in gastric glands
   HCO3
   - when combined forms a thick alkaline viscous layer of mucus that adheres to the epithelium
2. epithelial cells have a high turnover
3. prostaglandins maintain the mucosal blood flow supplying the epithelia with nutrients

Question 18

what might breach the stomach defences and what will this lead to?

Answer 18

alcohol- dissolves mucous layer
helicobacter pylori- chronic active gastritis
NSAIDS- inhibit prostaglandins

leads to gastritis, ulceration or reflux disease

Question 19

outline how gastric acid secretions may be reduced by drugs?

Answer 19

H2 blockers- cimetidine, ranitidine - stops histamine affecting parietal cells
PPI- proton pump inhibitors- omeprazole

highly selective vagotomy- will till need drain in as pyloric sphincter cannot relax