Stomach Flashcards
Muscularis Externa
3 layers of muscle
1. Inner oblique: Found in the cardiac stomach and strips along the greater and lesser curvatures
2. Middle circular: through the entire stomach
3. Outer longitudinal: Start and end of the stomach
Neuronal control
Autonomic NS: PNS and SNS(Via. mainly submucosal plexus and myenteric plexus)
neuronal afferents:
-lumen pH
-osmolarity
-calorie content
-types of macro-nutrients
-stretch of wall
-temperature
-painful stimuli
Orad/Proximal stomach
FUNCTIONS:
-food storage up to 1 hr
-food stored as layers top(newest) to bottom(oldest)
NOTE:
-Prior to loading upper stomach(FASTED) the muscle is contracted(Em=-40mV[Fasted] Vs. Em=-50mV[Fed]) which has a pressure of 13mmHg
-AFTER swallowing meal–> the upper stomach relaxes for 20-30mins(9.8mmHg-10mmHg)
(TRIGGERS)
a). Receptive relaxation: act of swallowing induces relaxation(Vagus/PNS input mediates)
b). Gastric accommodation: stretching of stomach wall
Caudad/Distal Stomach
FUNCTIONS:
-gastric emptying
-grinds foodstuff and mixes with enzymes and HCL
NOTE:
-smooth muscle cells prior to foodstuff entry are hyperpolarized(-70mV)
Cells contract –> Peristalsis(starts from top to down towards pyloric sphincter
-PNS activity INCREASED
-SNS activity DECREASED
-Food entering
Tituration: Retropulsion of foodstuff through a smaller bore hole via. peristalsis after hitting pyloric sphincter
Lag phase
how low it takes for the contents of stomach to get emptied into small intestine
Fed motor activity
FACTORS:
1. toughness of food
2. calorie content
3. viscosity
REGULATORS:
1. size particles: touch sensitive neurons –>brainstem –> INCREASE PNS
2. chemical from food: sensory input goes to brainstem and enteric NS –>MAYBE INCREASE gastrin and CCK secretions
3. Duodenum: wall stretch, fats, AA, L-tryptophan –>inhibits
Fasted motor activity
3 Phases(Migrating motor complex(MMC))
1. motor quiescence(75-90mins)
2. peristalsis(irregular and 15mins)
3. strong rhythmic contraction, starts at fundus –> stomach –> small intestine or pyloric sphincter –>open jejunum(5-15mins)
Pyloric sphincter
FUNCTIONS:
-regulates gastric emptying
-prevent reflux from small intestine to stomach
STRUCTURE:
-all circular muscle
-lots of vagal(PNS) input
REGULATORS:
1. Hormonal
-CCK, GLP-1 cause slow gastric emptying
-High fat and AA in duodenum –>closes
-High [H+] in duodenum –>closes
-High osmolarity –>closes
2. Sensory neurons
-sensory neurons(extrinsic) vagal, spinal afferents –>info sent to brainstem and spinal cord
-high SNS input –>contraction
-PNS: low frequency –>Closes Vs. High frequency –>Opens
3. Duodenum
-electrically stimulated duodenum contraction –>pyloric sphincter contracts too
4. Antrum
-electrically stimulate antrum –> Pyloric sphincter relaxes
Gastric emptying
Rate of emptying: 200 Kcal/hr
NOTE:
-liquids have no lag phase
-indigestible solids empty out last
LIQUIDS:
1. Calorie: slows
2. Volume: Larger volumes empty faster than small volume
3. Fat content: slows
4. Osmolarity/Tonicity: Hyper slows down emptying
5. L-trytophan: slows
6. pH: Acidity slows
7. gravity: no effect
SOLIDS:
-lag phase if anything is bigger than 1mm in diameter anything bigger than 0.25 mm in diameter have no lag phase
1. Calorie: slows
2. Volume: Larger volumes empty faster than small volume
3. Fat content: slows
4. Osmolarity/Tonicity: Hyper slows down emptying
6. pH: Acidity slows
Fluid Dynamics:
midline to pyloric sphincter is smallest particles and moving outward towards the edge is larger and larger all due to peristalsis
