Meal Phases: Gastric Flashcards
(67 cards)
1
Q
stomach
A
dilated part of the canal between esophagus and small intestine
2
Q
simple stomach
A
single compartment
3
Q
complex/ruminant stomach
A
multiple compartments
4
Q
functions of the stomach
A
- storage
- mixing
- H+ secretion
- delivery
- intrinsic factor secretion
5
Q
lesser curvature
A
concave curve (along top surface between pylorus and cardia)
6
Q
greater curvature
A
convex curve (along bottom between fundus and antrum)
7
Q
lower esophageal sphincter
A
cardiac sphincter; opening between the esophagus and the cardia of the stomach
8
Q
cardia
A
small area surrounding the LES
9
Q
function of the LES + cardia
A
prevent reflux
allow entry of food into stomach
regulate belching
10
Q
secretions in LES and cardiac region
A
mucus and bicarbonate
11
Q
fundus
A
part of the stomach that extends above the cardia from the cardiac incisure
12
Q
body of the stomach
A
corpus; extends from the cardia to the angular incisure
13
Q
function of the fundus and body
A
food reservoir
tonic force during emptying
14
Q
secretions in the fundus and body
A
H+, IF, mucus, bicarbonate, pepsinogens, lipase
15
Q
antrum
A
extends from the angular incisure to the pylorus
16
Q
pylorus
A
pyloric sphincter; opening between the stomach and the duodenum
17
Q
function of the antrum and pylorus
A
mixing
grinding
sieving
regulation of emptying
18
Q
secretions of the antrum and pylorus
A
mucus and bicarbonate
19
Q
rugal folds
A
allow the stomach to expand to accommodate more food
20
Q
cardiac region histology
A
simple glands that only contain mucin secreting cells
21
Q
antral region histology
A
enteroendocrine cells + simple glands that only contain mucin secreting cells
22
Q
body region histology
A
complex gastric glands with many cell types
23
Q
gastric glands
A
contain parietal and chief cells
24
Q
gastric pits
A
contain surface/neck cells
25
surface/neck cells
secrete mucin; located in the neck of the gastric gland (gastric pit)
26
parietal cells
secrete acid
located in proximal part of gland
have large canaliculi to maximize transit across cell
27
chief cells
secrete pepsinogen/digestive enzymes
located in distal part of gland
have large, apical granules containing pepsinogen
28
enteroendocrine cells
secrete histamine
located throughout the cell
29
steps of acid secretion
1. parietal cells break down H2O --> OH- + H+
2. carbonic anhydrase produces HCO3-
3. H+/K+ ATPases pump H+ across the apical side into the stomach lumen (against concentration gradient)
4. Cl- is pumped into the cell in exchange for HCO3- on basal side; HCO3- enters blood
5. Cl- crosses the cell and passes into the lumen on the apical side via Cl- channels
30
parietal cell stimulators
1. ACh: released by enteric neurons --> binds to cholinergic receptors on parietal cells
2. histamine: released by enteroendocrine cells --> bind to H2 receptors on parietal cells
3. gastrin: released by G cells in response to GRP --> binds to parietal cells and enteroendocrine cells
31
parietal cell inhibitor
somatostatin: released by D cells in response to acid in antrum --> binds to G cells to inhibit gastrin secretion --> decreases acid release in antrum
32
steps of pepsinogen secretion
1. H+ in lumen of the stomach stimulates ENS reflex
2. enteric neurons activate chief cells to release pepsinogen and lipase
3. pepsinogen gets activated to form pepsin by H+ in the lumen
33
chief cell stimulator
ACh: released by enteric neurons --> binds to chief cells
34
vago-vagal reflex
1. sensory neurons detect stretch of gastric wall --> activates parasympathetic outflow to stomach
2. PS outflow stimulates ENS neurons
3. enteric neurons stimulate acid and pepsinogen secretion
35
gastric erosion
superficial (partial) breakdown of mucosa
36
gastric ulceration
full thickness breakdown of mucosa; includes submucosa +/- muscularis
37
causes of ulceration
imbalance of aggressive factors and protective factors
38
protective mechanisms of the stomach
1. tight junctions
2. mucus
3. bicarbonate
4. prostaglandins (PGE2)
- increases blood flow, mucus/bicarb secretions, and epithelial cell proliferation
39
effect of NSAIDs on gastric protection
NSAIDs decrease prostaglandin production --> decreased mucosal defense
40
gastric therapies
1. histamine blockers (H2)
2. proton pump inhibitors (blocks H+/K+ ATPase)
3. antacids
41
what 3 cell types are needed for GI motility
enteric neurons
interstitial cells of cajal (ICCs)
smooth muscle cells
42
slow waves
intrinsic electrical activity in smooth muscle; periodic depolarizations that set up electrical conditions for smooth muscle cells to contract in response to ACh release from excitatory myenteric neurons
43
do slow waves reach threshold
no
44
what generates slow waves
ICCs in pacemaker regions (longitudinal muscle and myenteric plexus)
45
what does the amplitude and frequency of slow waves depend on
location in the GI tract
(antrum, small intestine, colon)
46
function of slow waves
to organize depolarization events into a pattern of phasic contractions
47
function of gap junctions
connect ICCs to other ICCs and smooth muscle cells
areas of low resistance to allow excitatory signal to propagate to neighboring cells
48
what type of ion channels do smooth muscle cells have that allow for contraction
L-type Ca2+ channels
49
does excitation spread to ICCs or smooth muscle first
ICCs --> coordinates pattern --> sends to smooth muscle
50
what modulates smooth muscle contraction
calcium (intra and extracellular)
ICCs set the pattern - action potential fires in same pattern as non-AP generating slow waves
51
what regulates smooth muscle contraction (frequency and tone)
enteric nervous system
52
anatomic regions of the stomach
fundus, corpus, antrum, pylorus
53
is muscle in the fundus thick or thin
thin - mixing function only
54
is muscle in the antrum thick or thin
thick - retropulses food back to body and involved in gastric emptying
55
is muscle in the pylorus thick or thin
thick - (circular muscle) has tonic contractions to prevent flow
tonic contraction generates HIGH pressure
56
functional regions of the stomach
gastric reservoir and gastric pump
57
what type of contractions occur in gastric reservoir region
tonic - fundus and body
58
what type of contractions occur in the gastric pump region
phasic - antrum
59
steps of gastric motility
1. relaxation of LES and cardia
2. tonic contraction of LES
3. relaxation of proximal stomach (fundus and body)
4. phasic contraction of distal stomach (antrum)
5. tonic contraction of pylorus
60
steps of gastric emptying
1. tonic contraction of proximal stomach (fundus and body)
2. increased strength of phasic contractions of antrum
3. relaxation of pylorus
4. receptive relaxation of SI (inhibits duodenal contraction)
creates high pressure in stomach and low pressure in SI --> liquids/semi-liquid chyme flows from high to low pressure
61
predominant reflex during gastric phase
receptive relaxation
62
regulation of gastric emptying
allows gastric emptying to slow depending on nutrient/energy content of food to maximize nutrient absorption
afferents:
enteroendocrine cells & vagal afferents: sense nutrients, H+ and hyperosmolarity of food
efferents:
activation of vagal outflow decreases strength of antral contractions, contracts pylorus, and decreases proximal motility to SLOW gastric emptying
63
sieving function of stomach
liquids empty faster than large particles
- can empty through SMALL pyloric opening
- large particles get pushed back
64
rate of liquid emptying
exponential rate
65
rate of solid emptying
lag phase followed by linear rate
66
how stomach increases rate of emptying
1. tonic contraction of reservoir
2. deep peristaltic waves of body
3. deep contractions of antral waves
4. wide pyloric opening
5. duodenal receptive relaxation
67
how stomach decreases rate of emptying
1. prolonged relaxation of reservoir
2. shallow peristaltic waves of body
3. shallow antral waves
4. small pyloric opening
5. lack of duodenal relaxation
