2 Stomach EmptyingStomach emptying is promoted by intense peristaltic contractions in the stomach antrumAt the same time, emptying is opposed by varying degrees of resistance to passage of chyme at the pylorus
3 Intense Antral Peristaltic Contractions During Stomach Emptying—“ Pyloric Pump.” Begins in midstomach & spreads through the caudad stomach 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.”
4 Role of the Pylorus in Controlling Stomach Emptying The thickness of the circular wall muscle becomes 50 to 100 percent greaterIt remains slightly tonically contracted almost all the timeThe constriction usually prevents passage of food particles until they have become mixed in the chyme to almost fluid consistencycontrolled by a very complex set of neural and hormonal signals
5 Regulation of Gastric Emptying Chyme must enter duodenum at proper rate
6 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.
8 Gastric Factors That Promote Emptying Effect of Gastric Food Volume on Rate of EmptyingStretching of the stomach wall elicit local myenteric reflexes in the wall that greatly accentuate activity of the pyloric pump and at the same time inhibit the pylorusDegree of fluidity of chyme
9 Gastric Factors That Promote Emptying Effect of the Hormone Gastrin on Stomach EmptyingRelease of a hormone called gastrin from the antral mucosaenhance the activity of the pyloric pump
11 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 of chyme in the duodenum becomes too much.
12 Regulation of Gastric Emptying Activation of receptors in intestinal mucosa initiates enterogastric reflexes. This decreases gastric emptying by -Inhibition of pyloric pumpIncreased tone of pyloric sphincter
13 Enterogastric Nervous Reflexes Directly from the duodenum to the stomach through the enteric nervous system in the gut wallThrough extrinsic nerves that go to the prevertebral sympathetic ganglia and then back through inhibitory sympathetic nerve fibers to the stomachSlightly through the vagus nerves all the way to the brain stem, where they inhibit the normal excitatory signals transmitted to the stomach through vagi
14 Factors responsible for enterogastric inhibitory reflex The degree of distention of the duodenumThe presence of any degree of irritation of the duodenal mucosaThe degree of acidity of the duodenal chymeThe degree of osmolality of the chymeThe presence of certain breakdown products in the chyme, especially breakdown products of proteins and perhaps to a lesser extent of fats
15 Role of Fats and the Hormone Cholecystokinin Hormone 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
17 Emotions can influence gastric motility Influence gastric emptying through autonomic nerves by influencing the gastric smooth muscle contractilityIntense pain can also inhibit the gastric motility by stimulation of sympathetic nerves