Stomach Emptying
Stomach emptying is promoted by intense peristaltic contractions in the stomachantrumAt the same time, emptying is opposed by varying degrees of resistance to passage ofchymeat the pylorus
IntenseAntralPeristaltic Contractions During Stomach Emptying—“ Pyloric Pump.”Begins inmidstomach& spreads through thecaudadstomach no longer as weak mixing contractions but as strong peristaltic, very tight ring like constrictions that can cause stomach emptyingThese intense peristaltic contractions create 50 to 70 centimeters of water pressureThe peristaltic waves, in addition to causing mixing in the stomach, also provide a pumping action called the “pyloric pump.”
Role of the Pylorus in Controlling Stomach Emptying
The thickness of the circular wall muscle becomes 50 to 100 percent greaterIt remains slightlytonicallycontracted almost all the timeThe constriction usually prevents passage of food particles until they have become mixed in thechymeto almost fluid consistencycontrolled by a very complex set of neural and hormonal signals
Regulation of Gastric Emptying
Chymemust enter duodenum at proper rate
Regulation of Gastric Emptying
Gastric emptying takes about 3 hours and very closely regulated so that nutrient absorption is maximized and H+ in the duodenum has time to be neutralized.Fat and high H+ (acidic) content slow gastric emptying.
Within the Stomach
Gastric Factors That Promote Emptying
Effect of Gastric Food Volume on Rate ofEmptyingStretching of the stomach wall elicit localmyentericreflexes in the wall that greatly accentuate activity of the pyloric pump and at the same time inhibit the pylorusDegree of fluidity ofchyme
Gastric Factors That Promote Emptying
Effect of the HormoneGastrinon Stomach EmptyingRelease of a hormone calledgastrinfrom theantralmucosaenhance the activity of the pyloric pump
With in the Duodenum
When food enters the duodenum multiple nervous reflexes are initiated from the duodenal wall that pass back to the stomach to slow or even stop stomach emptying if the volume ofchymein the duodenum becomes too much.
Regulation of Gastric Emptying
Activation of receptors in intestinal mucosa initiatesenterogastricreflexes. This decreases gastric emptying by -Inhibition of pyloric pumpIncreased tone of pyloric sphincter
EnterogastricNervous Reflexes
Directly from the duodenum to the stomach through the enteric nervous system in the gut wallThrough extrinsic nerves that go to theprevertebralsympathetic ganglia and then back through inhibitory sympathetic nerve fibers to the stomachSlightly through thevagusnerves all the way to the brain stem, where they inhibit the normal excitatory signals transmitted to the stomach throughvagi
Factors responsible forenterogastricinhibitory reflex
The degree of distention of the duodenumThe presence of any degree of irritation of the duodenal mucosaThe degree of acidity of the duodenalchymeThe degree ofosmolalityof thechymeThe presence of certain breakdown products in thechyme, especially breakdown products of proteins and perhaps to a lesser extent of fats
Role of Fats and the HormoneCholecystokininHormone released from the upper intestineStimulus for releasing these inhibitory hormones is mainly fats entering the duodenumBind with “receptors” on the epithelial cellsCarried by blood to the pylorus and increase the strength of contraction of the pyloric sphincter
Outside the digestive tract
Emotions can influence gastric motilityInfluence gastric emptying through autonomic nerves by influencing the gastric smooth muscle contractilityIntense pain can also inhibit the gastric motility by stimulation of sympathetic nerves
Inhibitory Hormonal Factors
CholecystokininSecretinGIP
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