Gastric motility and emptying Flashcards
How is motility in the stomach initially brought about
By reflex receptive relaxation, allowing food to enter from oes.
mediated by vagal inhibitory fibres
Where does mixing of food w secretions take place
In distal body and antrum of stomach. Muscularis externa here is thicker.
Contractions and relaxations of the 3 muscle layers cause the mixing and emptying
Which is the plexus resposible for the contractions
Myenteric plexus
3D layer between the layers of smooth muscle that recieves para and symp innervation
Where does parasymp innervation come from and what does it cause
Cholinergic from vagus
increase gastric motility and secretion
Where does symp innervation come from and what does it cause
Adrenergic from coeliac plexus has opposite effect
What happens when food stretches stomach
Cagovagal reflex reduces the tone in muscular wall of body of the stomach so wall bulges outwards.
Can accommodate more food, 0.8 L to 1.5L
Pylorus
As each peristaltic wave approaches pylorus, the pyloric muscle itself contracts to stop emptying through the pylorus. Therefore most antral contents are squeezed upstream again
- Initial lag phase
when stomach is full of food
not contracting, intense secretions are digesting food down to form chyme
- Reversal of vagal discharge
upregulation in vagal excitatorty and less inhibitory
contractions break off small boluses of food and carry towards pylorus
large pieces moved back up for further degradation (retropulsion)
what does force and freq of contractions depend on
- neural activity of intrinsic and extrinsic nerves
- myogenic properties of smooth muscle
- properties of paracrine andendocrine agents (gastrin and motilin upregulate foc, secretin inhibits)
basic electrical rhythm of stomach
pacemaker zone located in fundus on greater curvature
these cells spontaneously depolrize, continuously
Depending on excitability of smooth muscle, BER may trigger large peristaltic waves
sweep down towards antrum, where greatest contraction occurs
Contraction rate and time
3 per minute
last between 2 and 20 seconds
Gastric emptying
pyloric sphincter
circular muscle of pylorus is greater and remains tonically contracted at all times
As retropulsion occurs, the pyloric sphincter opens by coordination of antral and duodenal contractions. small digested particles squirted through
Pyloric pump
As stomach becomes progressively more empty, the contractions begin farther and farther up the body of the stomach, gradually pinching off the food in body to push to antrum
Factors that determine rate of gastric emptying
type of food eaten
osmotic pressure of duodenal contents
vagal innervation
release of somatostatin, secretin, CCK and GIP by duodenum (all inhibit emptying)
