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GI > Physiology of Gastric Motility and Gastric Acid Secretion > Flashcards

Physiology of Gastric Motility and Gastric Acid Secretion Flashcards

1
Q

what is the role of the stomach

A

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

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2
Q

name the two regions of the stomach

A

orad region

caudad region

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3
Q

where is the orad region

A

fundus to proximal body

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4
Q

where is the caudad region

A

distal body and antrum

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5
Q

explain what happens in the orad region

A

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

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6
Q

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

A

via weak phasic contractions

phasic contractions are weak due to relatively thin muscular wall

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7
Q

what is the role of gastrin

A

decreases the rate of gastric emptying

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8
Q

what happens at the caudad region

A

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

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9
Q

explain retropulsion

A

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

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10
Q

what is the slow wave eliciting the contraction AKA

A

antral wave or pump

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11
Q

what has an effect on gastric emptying

A

gastric and dodenal factors

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12
Q

list some gastric factors

A

consistency of chyme

proportional to volume of chyme

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13
Q

list some duodenal factors

A 
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
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14
Q

describe the gastric mucosa

A

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

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15
Q

the stomach can be split into

A

oxyntic gland and pyloric gland

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16
Q

pyloric gland has what kind of cells

A

D cells - secrete somatostatin

G cells - secretes gastrin

17
Q

oxyntic mucosa has what kind of cells

A

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

18
Q

what is the role of HCl

A

pepsinogen –> pepsin
denature proteins
kill most micro-organisms

19
Q

what type of cells does Hcl acid come from

A

parietal cells

20
Q

intrinsic factor is responsible for

A

binding Vit B12

21
Q

Gastroferrin is responsible for

A

binding Fe2+

22
Q

What is pepsinogen

A

inactive precursor of pepsin

23
Q

the role of histamine

A

stimulate HCl acid secretion

24
Q

G cells

A

secrete HCl

25
Q

Somatostatin

A

inhibits HCl

26
Q

Mucus

A

Protective

27
Q

How is hydrochloric acid secreted

A

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

28
Q

what induces acid secretion

A

Acetylcholine
gastrin
histamine

29
Q

how do acetylcholine, gastrin and histamine act

A

via direct and indirect mechanisms

30
Q

Direct pathway

A

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

31
Q

indirect mechanism

A

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

32
Q

by what mechanism does gastrin and acetylcholine work

A

activates PLC –> IP3 –> H

33
Q

by what mechanism does histamine work

A

activates cAMP which activates PKa –> H

34
Q

by which mechanisms do somatostatin and prostaglandin inhibit H secretion

A

preventing cAMP activating pKa and thereby preventing H entering the lumen

35
Q

what are the 3 phases of gastric acid secretion

A

cephalic
gastric
intestinal

36
Q

describe the stimulatory effects of gastric motility

A

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

37
Q

describe the inhibitory effects of gastric motility

A

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

38
Q

Explain in detail the cephalic phase

A

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

39
Q

Explain in detail gastric phase

A

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

GI (25 decks)

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