Gastric Motility, Secretion and Digestion

Question 1

capacity of the stomach

Answer 1

orad region relaxes receptively to accomadate food from oesophagus

Question 2

what nerve relaxes the stomach

Answer 2

vagus (CN X)

Question 3

functions of the stomach

Answer 3

digestion;
proteins
carbohydrates

mixes food with gastric secretions, producing chyme

limited amount of absorption

stores food before passing to small intestine

Question 4

enzymes for protein digestion

Answer 4

pepsin

HCl

Question 5

enzymes for carbohydrate digestion

Answer 5

salivary amylase

Question 6

secretion of gastric juice from stomach

Answer 6

secretes gastric juice from gastric gland in the gastric mucosa

Question 7

describe fundus of the stomach

Answer 7

next to oesophagus

thin smooth muscle layer

Question 8

function of fundus

Answer 8

receives food, little mixing

little food stored here - usually a pocket of gas

Question 9

describe body of the stomach

Answer 9

middle section

thin smooth muscle layer

Question 10

function of body

Answer 10

little mixing

food stored here

Question 11

describe antrum of stomach

Answer 11

next to duodenum

thick smooth muscle layer

Question 12

function of antrum

Answer 12

highly contractile

much mixing at time of gastric secretions

Question 13

mechanical activity of the stomach

Answer 13

2 types;
orad stomach
caudad stomach

Question 14

describe orad stomach

Answer 14

fundus and proximal body

tonic - maintained

Question 15

describe caudad stomach

Answer 15

distal body and antrum

phasic - intermittent

Question 16

electrical and mechanical activity of the orad region - relaxation

Answer 16

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

Question 17

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

Answer 17

gastrin

Question 18

electrical and mechanical activity of caudad region

Answer 18

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

Question 19

what controls the emptying of the stomach

Answer 19

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

Question 20

what governs the strength of the antral wave

Answer 20

gastric factors

duodenal factors

Question 21

gastric factors

Answer 21

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

Question 22

gastric factors - how does distension increase motility

Answer 22

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

Question 23

duodenal factors

Answer 23

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

Question 24

duodenal factors - how does the duodenum delay emptying

Answer 24

neuronal response - entergastric reflex

hormonal response - release of enteragastrones

Question 25

enterogastric reflex

Answer 25

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

Question 26

enterogastrones

Answer 26

e.g. cholecystokinin CCK | inhibits stomach contraction

Question 27

stimuli within duedenom driving neuronal and hormones response

Answer 27

fat (potent) acid hypertonicity distension

Question 28

how does fat within duedenom drive neuronal and hormones response

Answer 28

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

Question 29

how does acid within duedenom drive neuronal and hormones response

Answer 29

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

Question 30

how does hypertonicity within duedenom drive neuronal and hormones response

Answer 30

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

Question 31

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

Answer 31

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

Question 32

what is gastric mucosa composed of

Answer 32

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

Question 33

functions of oxyntic mucosa

Answer 33

``` secretes; HCl pepsinogen intrinsic factor and Gastroferrin histamine mucus ```

Question 34

HCl function in secretion

Answer 34

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

Question 35

pepsinogen function in secretion

Answer 35

inactive precursor of the peptidase, pepsin

Question 36

intrinsic factor and gastroferrin function in secretion

Answer 36

bind vitamin B12 and iron respectively, facilitating subsequent absorption

Question 37

histmaine function in secretion

Answer 37

stimulates HCl secretion

Question 38

somatostatin function in secretion

Answer 38

inhibits HCl secretion

Question 39

what regulates/induces HCl secretion from gastric parietal cell

Answer 39

ACh gastrin (parietal cell) histamine

Question 40

functions of pyloric gland area secretion

Answer 40

gastrin somatostatin mucus

Question 41

gastrin function in secretion

Answer 41

stimulates HCl secretion

Question 42

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

Answer 42

gastrin, ACh - PLC-IP3 | histamine - cAMP PKA

Question 43

receptor and signal-transduciton pathways for inhibiting HCl from gastrin

Answer 43

somatostatin, prostaglandins - cAMP - PKA

Question 44

3 phases of gastric acid secretion

Answer 44

``` cephalic phase (in the head) gastric phase intestinal phase ```

Question 45

cephalic phase

Answer 45

before food reaches the stomach preparing it stomach to receive food

Question 46

nerve control of cephalic phase - neurotransmitter action

Answer 46

``` vagus nerve (CN X); release ACh - directly activating parietal cells ```

Question 47

gastric phase

Answer 47

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

Question 48

intestinal phase

Answer 48

after food has left stomach; | chyme entering upper small intestine causes weak stimulation of gastric secretion via neuronal and hormonal mechanisms

Question 49

nerve control of cephalic phase - endocrine action

Answer 49

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

Question 50

nerve control of cephalic phase - paracrine action

Answer 50

vagus nerve; | via release of histmaine from ECL cells that locally activate parietal cells

Question 51

nerve control of cephalic phase - D cells

Answer 51

vagus nerve; | via inhibition of D cells, decreasing the inhibitory effect of ss on G-cells

Question 52

physical and chemical mechanisms of the gastric phase

Answer 52

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

Question 53

phases of inhibition of gastric acid secretion

Answer 53

cephalic phase gastric phase intestinal phase

Question 54

phases of inhibition of gastric acid secretion - cephalic phase

Answer 54

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

Question 55

phases of inhibition of gastric acid secretion - gastric phase

Answer 55

``` 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 ```

Question 56

phases of inhibition of gastric acid secretion - intestinal phase

Answer 56

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