Physiology of Gastric Motility and Gastric Acid Secretion

Question 1

what is the role of the stomach

Answer 1

stores food before passing food on to small intestine as chyme
continues carbohydrate digestion
begins protein digestion

Question 2

name the two regions of the stomach

Answer 2

orad region

caudad region

Question 3

where is the orad region

Answer 3

fundus to proximal body

Question 4

where is the caudad region

Answer 4

distal body and antrum

Question 5

explain what happens in the orad region

Answer 5

vagus nerve causes relaxation leading to the opening of the lower oesophageal sphincter
this allows food to move in to the cuadad part of the stomach where it is stored
minimal mixing of contents leads. to
protein digestion begins here
carbohydrate digestion continues

Question 6

how do contents from the orad region lead to the caudad region of the stomach

Answer 6

via weak phasic contractions

phasic contractions are weak due to relatively thin muscular wall

Question 7

what is the role of gastrin

Answer 7

decreases the rate of gastric emptying

Question 8

what happens at the caudad region

Answer 8

slow waves occur simultaneously but only those reaching threshold will illicit contraction
propels contents from mid stomach –> gastroduodenal junction

Question 9

explain retropulsion

Answer 9

increased velocity of contraction approaching the gastroduodenal junction overtaking chyme movement
small amounts of chyme and small particles pass through

Question 10

what is the slow wave eliciting the contraction AKA

Answer 10

antral wave or pump

Question 11

what has an effect on gastric emptying

Answer 11

gastric and dodenal factors

Question 12

list some gastric factors

Answer 12

consistency of chyme

proportional to volume of chyme

Question 13

list some duodenal factors

Answer 13

fat - delay gastric emptying
products of protein and carbohydrate digestion can draw water into the. small intestine and decrease plasma volume 
hormonal relex
enterogatstric reflex
acid - time for neutralisation

Question 14

describe the gastric mucosa

Answer 14

surface lining the stomach
pits, invaginations of the surface
glands at the bottom of the its pits

Question 15

the stomach can be split into

Answer 15

oxyntic gland and pyloric gland

Question 16

pyloric gland has what kind of cells

Answer 16

D cells - secrete somatostatin

G cells - secretes gastrin

Question 17

oxyntic mucosa has what kind of cells

Answer 17

chief cells - secrete pepsinogen
mucous cells - secrete histamine
parietal cells - HCL, intrinsic factor, gastroferrin

Question 18

what is the role of HCl

Answer 18

pepsinogen –> pepsin
denature proteins
kill most micro-organisms

Question 19

what type of cells does Hcl acid come from

Answer 19

parietal cells

Question 20

intrinsic factor is responsible for

Answer 20

binding Vit B12

Question 21

Gastroferrin is responsible for

Answer 21

binding Fe2+

Question 22

What is pepsinogen

Answer 22

inactive precursor of pepsin

Question 23

the role of histamine

Answer 23

stimulate HCl acid secretion

Question 24

G cells

Answer 24

secrete HCl

Question 25

Somatostatin

Answer 25

inhibits HCl

Question 26

Mucus

Answer 26

Protective

Question 27

How is hydrochloric acid secreted

Answer 27

CO2 + H20 join to form H2CO3 by carbonic anhydrase H passes into the lumen via H/K ATPase K then flows back across K flows into the plasma via K+ channel and Na/KATPase Na flows out from inside the cell HCO3- exits the cell via HCO3/Cl antiporter CL enters the cell Cl enters the lumen via a chlorine channel CFTR Cl and H fuse together to form HCl

Question 28

what induces acid secretion

Answer 28

Acetylcholine gastrin histamine

Question 29

how do acetylcholine, gastrin and histamine act

Answer 29

via direct and indirect mechanisms

Question 30

Direct pathway

Answer 30

ACh, gastrin and histamine stimulates parietal cell --> brings H into lumen

Question 31

indirect mechanism

Answer 31

ACh and gastrin stimulate ECL cells to secrete histamine and histamine then activates the parietal cell to bring hydrogen into lumen

Question 32

by what mechanism does gastrin and acetylcholine work

Answer 32

activates PLC --> IP3 --> H

Question 33

by what mechanism does histamine work

Answer 33

activates cAMP which activates PKa --> H

Question 34

by which mechanisms do somatostatin and prostaglandin inhibit H secretion

Answer 34

preventing cAMP activating pKa and thereby preventing H entering the lumen

Question 35

what are the 3 phases of gastric acid secretion

Answer 35

cephalic gastric intestinal

Question 36

describe the stimulatory effects of gastric motility

Answer 36

cephalic - before food reaches stomach --> activation of the vagus nerve allows opening of the lower oesophageal sphincter gastric - mix of chemical and physical mechanisms when food is in the stomach intestinal - after food has left the stomach when chyme leaves the stomach

Question 37

describe the inhibitory effects of gastric motility

Answer 37

cephalic - inhibition of vagus nerve CNX --> constriction of lower oesophageal sphincter gastric - antral pH falls --> activates delta cells to release somatostatin --> stop gastric emptying gastric - release of prostaglandin E2 --> prevent histamine from HCl secretion

Question 38

Explain in detail the cephalic phase

Answer 38

slight smell, taste of food vagal activation --> enteric neurones Increased ACh increase parietal cells directly Increased ACh can stimulate ECL cells to increase histamine and stimulate parietal cells Increase in GRP can stimulate G cells to release gastrin and activate parietal cells Parietal cells increase secretion Increase in ACh can inhibit Delta cells from releasing somatostatin and therefore decrease its inhibitory effect on parietal cells

Question 39

Explain in detail gastric phase

Answer 39

when food is in the stomach Distension causes activation of mechanoreceptors which activate G cells to increase gastrin and thereby activate parietal cells Distension also causes increase in ACh and thereby activates parietal cells Increase pH causes inactivation of D cells and therefore decrease somatostatin and decrease inhibitory effect on parietal cells Protein digestion activates G cells to increase gastrin and thereby parietal cells