Gastric Motiliity and Secretion

Question 1

entrance and exit of the stomach

Answer 1

entrance = cardia
exit = pyloric sphincter after the antrum

Question 2

mucosa and submucosa of stomach highly folder, called? function?

Answer 2

ruggae, allows dramatic increase in stomach volume.

Question 3

two regions of the stomach?

Answer 3

orad and caudad regions

Question 4

gastric motility receptive relaxation controlled by

Answer 4

vagus nerve, coordinates with stomachs enteric nerve plexus.

Question 5

neurotransmitters responsible for stomach relaxation

Answer 5

NO and serotonin

Question 6

what is retropulsion

Answer 6

powerful peristaltic stomach contractions force the pyloric sphincter closed, forcing the contents of the antrum backwards towards the body of the stomach.

Question 7

define basic electrical rhythm of the GI tract

Answer 7

smooth muscle cellls undergo spontaneous cycles of depolarisation and repolarisation

Question 8

slow waves; origin, mechanism, function

Answer 8

pacemaker zone of stomach, approx 3/minute, coordinate contractions by controlling the appearance of APs.

Question 9

ring of smooth muscle between antrum and duodenum

Answer 9

pyloric sphincter

Question 10

control of pyloric sphincter (3 thing)

Answer 10

Sympathetic nerve fibres increase constriction
Parasympathetic vagal fibres can be either excitatory or inhibitory to muscle contraction
Hormones cholecystokinin (CCK), gastrin, gastric inhibitory peptide (GIP) and secretin all cause constriction of the sphincter.

Question 11

which duodenal environments will decrease rate of stomach emptying, how does this occur

Answer 11

fat digestion products
highly acidic conditions
hypertonic conditions

receptors on duodenum/jejunum sensitive to the above cause release of enteric hormones causing constriction of p.sphincter/decrease antrum contractions.

Question 12

components of gastric juice, secreted by what structure, how much/day

Answer 12

HCl
Mucus
Enzymes (pepsinogen and gastric lipase)
intrinsic factor

gastric glands

3 litres

Question 13

2 cell types that secrete mucous

Answer 13

surface mucous cells and neck mucous cells.

Question 14

parietal cells secrete

Answer 14

HCl and intrinsic factor

Question 15

chief cells secrete

Answer 15

pepsinogen

Question 16

G cells secrete

Answer 16

gastrin

Question 17

where are parietal and G cells found

Answer 17

parietal - proximal 80% of stomach (“oxyntic gland area”)

G cells - typically in the antrum (“pyloric gland area”)

Question 18

3 gastric functions of gastrin

Answer 18

secretes acid, pepsinogen, mucus, HCO3-
stimulates gastric motility
inhibits gastric emptying

Question 19

3 effects of gastrin (outside stomach)

Answer 19

stimulation of pancreatic enzyme and HCO3- secretion
stimulation of insulin release
stimulation of intestinal motility

Question 20

Histamine is secreted by

Answer 20

Enterochromaffin like cells (ECL)

Question 21

2 actions of histamine in the stomach

Answer 21

stimulates acid secretion

increased local blood flow - supports increase in metabolism associated with acid secretion.

Question 22

somatostatin secreted by, found where

Answer 22

D cells, antrum and body of the stomach

Question 23

gastric effects of somatostatin

Answer 23

inhibits gastrin release

inhibits acid secretion

Question 24

pH of gastric lumen

Answer 24

1-2

Question 25

how is a parietal cell adapted for function

Answer 25

apex pointed towards gastric lumen
extensive invaginations forming canaliculi - large surface area
high mitochondria content

Question 26

mechanism of acid secretion (4 steps)

Answer 26

Carbonic anhydrase: CO2 + H20 –> H+ + HCO3-
H+ secreted in lumen by H+/K+ ATPase pump
HCO3- moves out of basolateral side of cell via antiport with Cl-
Cl- diffuses passively into stomach lumen by passive diffusion.

Question 27

3 things that stimulate acid secretion

Answer 27

gastrin
ACh
hsitamine

Question 28

3 things that inhibit acid secretion

Answer 28

somatostatin
prostaglandins
enteric hormones

Question 29

2 things that can function to increase histamine release

Answer 29

gastrin and ACh

Question 30

what is mucus

Answer 30

mixture of glycoproteins and glycopolysaccharides, functions to protect stomach against acid, proteolytic enzymes and mechanical damage.

Question 31

gastro-mucosal barrier consists of

Answer 31

mucus and HCO3-

Question 32

renewal of gastric mucosa controlled by

Answer 32

prostaglandins - inhibit acid secretion and increase mucus and HCO3- production
stimuli of acid secretion also increase mucus production
cells of stomach have a high rate of cell division

Question 33

what causes pepsinogen –> pepsin

Answer 33

low pH (only active at low pH)

Question 34

5 functions of the stomach

Answer 34

store food
minimize bacteria ingestion
dissolve and partially digest macromolecules
regulate rate of passage into duodenum
secrete intrinsic factor