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Gastrointestinal > Gastric Motility, Secretion and Digestion > Flashcards

Gastric Motility, Secretion and Digestion Flashcards

1
Q

capacity of the stomach

A

orad region relaxes receptively to accomadate food from oesophagus

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2
Q

what nerve relaxes the stomach

A

vagus (CN X)

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3
Q

functions of the stomach

A

digestion;
proteins
carbohydrates

mixes food with gastric secretions, producing chyme

limited amount of absorption

stores food before passing to small intestine

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4
Q

enzymes for protein digestion

A

pepsin

HCl

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5
Q

enzymes for carbohydrate digestion

A

salivary amylase

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6
Q

secretion of gastric juice from stomach

A

secretes gastric juice from gastric gland in the gastric mucosa

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7
Q

describe fundus of the stomach

A

next to oesophagus

thin smooth muscle layer

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8
Q

function of fundus

A

receives food, little mixing

little food stored here - usually a pocket of gas

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9
Q

describe body of the stomach

A

middle section

thin smooth muscle layer

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10
Q

function of body

A

little mixing

food stored here

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11
Q

describe antrum of stomach

A

next to duodenum

thick smooth muscle layer

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12
Q

function of antrum

A

highly contractile

much mixing at time of gastric secretions

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13
Q

mechanical activity of the stomach

A

2 types;
orad stomach
caudad stomach

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14
Q

describe orad stomach

A

fundus and proximal body

tonic - maintained

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15
Q

describe caudad stomach

A

distal body and antrum

phasic - intermittent

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16
Q

electrical and mechanical activity of the orad region - relaxation

A

occurs during swallow, permitting storage of ingested material
no slow activity
tonic contractions - weak due to relatively thin musculature

contents propelled intermittently to caudad region by low amplitude tonic contractions – decrease stomach size as it empties
minimal mixing of contents for long periods allows for carbohydrate partial digestion

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17
Q

hormone that decreases contractions (and stomach emptying) in the orad region

A

gastrin

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18
Q

electrical and mechanical activity of caudad region

A

slow waves occur simultaneously, only those that reach threshold contract
phasic peristaltic contractions driven by suprathreshold slow waves progress from midstomach to gastroduodenal junction (the antral wave, or pump) propelling contents towards pylorus through which a very small volume of chyme flows into the duodenum
velocity of contraction increases towards the junction, overtaking the movement of chyme that rebounds against constricted distal antrum back into the relaxed body of the stomach – this is retropulsion
retropulsion mixes gastric contents reducing chyme (‘grinding’ function) to small particles that pass through the pylorus

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19
Q

what controls the emptying of the stomach

A

strength of antral wave, or pump, determines the escape of chyme through pyloric sphincter

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20
Q

what governs the strength of the antral wave

A

gastric factors

duodenal factors

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21
Q

gastric factors

A

rate of emptying proportional to volume of chyme in the stomach - distension increases motility
consistency of chyme - emptying facilitated by thin liquid chyme

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22
Q

gastric factors - how does distension increase motility

A

stretch of smooth muscle
stimulation of intrinsic nerve plexus
increased vagus nerve activity and gastrin release

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23
Q

duodenal factors

A

duodenum must be ready to receive chyme, it can delay entry

24
Q

duodenal factors - how does the duodenum delay emptying

A

neuronal response - entergastric reflex

hormonal response - release of enteragastrones

25
Q

enterogastric reflex

A

decreases antral activity by signals from intrinsic nerve plexus and the ANS

26
Q

enterogastrones

A

e.g. cholecystokinin CCK

inhibits stomach contraction

27
Q

stimuli within duedenom driving neuronal and hormones response

A

fat (potent)
acid
hypertonicity
distension

28
Q

how does fat within duedenom drive neuronal and hormones response

A

delay in gastric emptying required for digestion and absorption in small intestine

29
Q

how does acid within duedenom drive neuronal and hormones response

A

time is required for neutralisation of gastric acid by bicarbonate secreted from the pancreas - important for optimal function of pancreatic digestive enzymes

30
Q

how does hypertonicity within duedenom drive neuronal and hormones response

A

products of carbohydrate and protein digestion are osmotically active and draw water into the small intestine - danger of reduced plasma volume and circulatory disturbances
e.g. dumping syndrome

31
Q

how is the mucosa of the stomach class in consideration of secretion

A

the oxyntic gland area (proximal stomach including the fundus and body)
the pylorlic gland area (distal stomach, designated the antrum)

32
Q

what is gastric mucosa composed of

A

surface lining the stomach
pits, invaginations of the surface
gland, at the base of the pits responsible for several secretions

33
Q

functions of oxyntic mucosa

A 
secretes;
HCl 
pepsinogen
intrinsic factor and Gastroferrin
histamine 
mucus
34
Q

HCl function in secretion

A

activates pepsinogen to pepsin
denatures protein
kills most micro-oragnisms ingested with food

35
Q

pepsinogen function in secretion

A

inactive precursor of the peptidase, pepsin

36
Q

intrinsic factor and gastroferrin function in secretion

A

bind vitamin B12 and iron respectively, facilitating subsequent absorption

37
Q

histmaine function in secretion

A

stimulates HCl secretion

38
Q

somatostatin function in secretion

A

inhibits HCl secretion

39
Q

what regulates/induces HCl secretion from gastric parietal cell

A

ACh
gastrin (parietal cell)
histamine

40
Q

functions of pyloric gland area secretion

A

gastrin
somatostatin
mucus

41
Q

gastrin function in secretion

A

stimulates HCl secretion

42
Q

receptor and signal-transduciton pathways for secretion of HCl from gastrin

A

gastrin, ACh - PLC-IP3

histamine - cAMP PKA

43
Q

receptor and signal-transduciton pathways for inhibiting HCl from gastrin

A

somatostatin, prostaglandins - cAMP - PKA

44
Q

3 phases of gastric acid secretion

A 
cephalic phase (in the head)
gastric phase 
intestinal phase
45
Q

cephalic phase

A

before food reaches the stomach preparing it stomach to receive food

46
Q

nerve control of cephalic phase - neurotransmitter action

A 
vagus nerve (CN X);
release ACh - directly activating parietal cells
47
Q

gastric phase

A

when food is in stomach - involving both physical and chemical mechanisms

48
Q

intestinal phase

A

after food has left stomach;

chyme entering upper small intestine causes weak stimulation of gastric secretion via neuronal and hormonal mechanisms

49
Q

nerve control of cephalic phase - endocrine action

A

vagus nerve;

via release of GRP, causing release of gastrin from G cells into systemic circulation - activating parietal cells

50
Q

nerve control of cephalic phase - paracrine action

A

vagus nerve;

via release of histmaine from ECL cells that locally activate parietal cells

51
Q

nerve control of cephalic phase - D cells

A

vagus nerve;

via inhibition of D cells, decreasing the inhibitory effect of ss on G-cells

52
Q

physical and chemical mechanisms of the gastric phase

A

distension of stomach activates reflexes that cause acid secretion
food buffers pH, D cel inhibition via ss of gastrin release is decreased
amino acids stimulate G cells
other stimulates - calcium, caffeine, alcohol

53
Q

phases of inhibition of gastric acid secretion

A

cephalic phase
gastric phase
intestinal phase

54
Q

phases of inhibition of gastric acid secretion - cephalic phase

A

vagal nerve activity decreases upon cessation of eating and following stomach emptying
pain, nausea and negative emotions also decrease vagal activity and increase sympathetic activity - reducing gastric secretion

55
Q

phases of inhibition of gastric acid secretion - gastric phase

A 
antral pH falls when food exits stomach (due to decreased buffering of gastric HCl) – release of somatostatin from D cells recommences, decreasing gastrin secretion
prostaglandin E2 (PGE2) continually secreted by the gastric mucosa acts locally to reduce histamine- and gastrin-mediated HCl secretion
56
Q

phases of inhibition of gastric acid secretion - intestinal phase

A

The factors that reduce gastric motility also reduce gastric secretion (e.g. neuronal reflexes, enterogastrones)

Gastrointestinal (71 decks)

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