Meal Phases: Gastric Flashcards
stomach
dilated part of the canal between esophagus and small intestine
simple stomach
single compartment
complex/ruminant stomach
multiple compartments
functions of the stomach
- storage
- mixing
- H+ secretion
- delivery
- intrinsic factor secretion
lesser curvature
concave curve (along top surface between pylorus and cardia)
greater curvature
convex curve (along bottom between fundus and antrum)
lower esophageal sphincter
cardiac sphincter; opening between the esophagus and the cardia of the stomach
cardia
small area surrounding the LES
function of the LES + cardia
prevent reflux
allow entry of food into stomach
regulate belching
secretions in LES and cardiac region
mucus and bicarbonate
fundus
part of the stomach that extends above the cardia from the cardiac incisure
body of the stomach
corpus; extends from the cardia to the angular incisure
function of the fundus and body
food reservoir
tonic force during emptying
secretions in the fundus and body
H+, IF, mucus, bicarbonate, pepsinogens, lipase
antrum
extends from the angular incisure to the pylorus
pylorus
pyloric sphincter; opening between the stomach and the duodenum
function of the antrum and pylorus
mixing
grinding
sieving
regulation of emptying
secretions of the antrum and pylorus
mucus and bicarbonate
rugal folds
allow the stomach to expand to accommodate more food
cardiac region histology
simple glands that only contain mucin secreting cells
antral region histology
enteroendocrine cells + simple glands that only contain mucin secreting cells
body region histology
complex gastric glands with many cell types
gastric glands
contain parietal and chief cells
gastric pits
contain surface/neck cells
surface/neck cells
secrete mucin; located in the neck of the gastric gland (gastric pit)
parietal cells
secrete acid
located in proximal part of gland
have large canaliculi to maximize transit across cell
chief cells
secrete pepsinogen/digestive enzymes
located in distal part of gland
have large, apical granules containing pepsinogen
enteroendocrine cells
secrete histamine
located throughout the cell
steps of acid secretion
- parietal cells break down H2O –> OH- + H+
- carbonic anhydrase produces HCO3-
- H+/K+ ATPases pump H+ across the apical side into the stomach lumen (against concentration gradient)
- Cl- is pumped into the cell in exchange for HCO3- on basal side; HCO3- enters blood
- Cl- crosses the cell and passes into the lumen on the apical side via Cl- channels
parietal cell stimulators
- ACh: released by enteric neurons –> binds to cholinergic receptors on parietal cells
- histamine: released by enteroendocrine cells –> bind to H2 receptors on parietal cells
- gastrin: released by G cells in response to GRP –> binds to parietal cells and enteroendocrine cells
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
steps of pepsinogen secretion
- H+ in lumen of the stomach stimulates ENS reflex
- enteric neurons activate chief cells to release pepsinogen and lipase
- pepsinogen gets activated to form pepsin by H+ in the lumen
chief cell stimulator
ACh: released by enteric neurons –> binds to chief cells
vago-vagal reflex
- sensory neurons detect stretch of gastric wall –> activates parasympathetic outflow to stomach
- PS outflow stimulates ENS neurons
- enteric neurons stimulate acid and pepsinogen secretion
gastric erosion
superficial (partial) breakdown of mucosa
gastric ulceration
full thickness breakdown of mucosa; includes submucosa +/- muscularis
causes of ulceration
imbalance of aggressive factors and protective factors
protective mechanisms of the stomach
- tight junctions
- mucus
- bicarbonate
- prostaglandins (PGE2)
- increases blood flow, mucus/bicarb secretions, and epithelial cell proliferation
effect of NSAIDs on gastric protection
NSAIDs decrease prostaglandin production –> decreased mucosal defense
gastric therapies
- histamine blockers (H2)
- proton pump inhibitors (blocks H+/K+ ATPase)
- antacids
what 3 cell types are needed for GI motility
enteric neurons
interstitial cells of cajal (ICCs)
smooth muscle cells
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
do slow waves reach threshold
no
what generates slow waves
ICCs in pacemaker regions (longitudinal muscle and myenteric plexus)
what does the amplitude and frequency of slow waves depend on
location in the GI tract
(antrum, small intestine, colon)
function of slow waves
to organize depolarization events into a pattern of phasic contractions
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
what type of ion channels do smooth muscle cells have that allow for contraction
L-type Ca2+ channels
does excitation spread to ICCs or smooth muscle first
ICCs –> coordinates pattern –> sends to smooth muscle
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
what regulates smooth muscle contraction (frequency and tone)
enteric nervous system
anatomic regions of the stomach
fundus, corpus, antrum, pylorus
is muscle in the fundus thick or thin
thin - mixing function only
is muscle in the antrum thick or thin
thick - retropulses food back to body and involved in gastric emptying
is muscle in the pylorus thick or thin
thick - (circular muscle) has tonic contractions to prevent flow
tonic contraction generates HIGH pressure
functional regions of the stomach
gastric reservoir and gastric pump
what type of contractions occur in gastric reservoir region
tonic - fundus and body
what type of contractions occur in the gastric pump region
phasic - antrum
steps of gastric motility
- relaxation of LES and cardia
- tonic contraction of LES
- relaxation of proximal stomach (fundus and body)
- phasic contraction of distal stomach (antrum)
- tonic contraction of pylorus
steps of gastric emptying
- tonic contraction of proximal stomach (fundus and body)
- increased strength of phasic contractions of antrum
- relaxation of pylorus
- 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
predominant reflex during gastric phase
receptive relaxation
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
sieving function of stomach
liquids empty faster than large particles
- can empty through SMALL pyloric opening
- large particles get pushed back
rate of liquid emptying
exponential rate
rate of solid emptying
lag phase followed by linear rate
how stomach increases rate of emptying
- tonic contraction of reservoir
- deep peristaltic waves of body
- deep contractions of antral waves
- wide pyloric opening
- duodenal receptive relaxation
how stomach decreases rate of emptying
- prolonged relaxation of reservoir
- shallow peristaltic waves of body
- shallow antral waves
- small pyloric opening
- lack of duodenal relaxation
