Question

discuss the regulation of gastric secretion, gastric mobility and gastric emptying. Include both neural and chemically mediated processes and mechanisms for both stimulation and inhibition

Answer 1

There are two phases for gastric secretion stimulation. They are cephalic phase and gastric phase. In cephalic phase it is stimulated by eating food and gastric phase is stimulated by the arriver of food in the stomach.Another phase that controls gastric secretion when food arrives the small intestine is called intestinal phase.All these stimulating factors secretes fluids that contains hydrochloric acid,electrolytes, pepsinogen, ,bicarboante and mucus.In this the hydrochloric acid and pepsinogen stimulates oral and gastric vagal afferents.This results in the release of gastrins , a digestive hormone secreted by the area where the stomach joins the small intestine.This triggers the secretion of gastric juice.As digestion proceeds gastric acid continue to release until the food leaves the stomach.Then finally when the contents that is leaving the stomach after digestion reaches a pH level below 2.5 and thus the release of gastrin is stopped which in turn inhibits the acid secretion.

Gastric mobility or Gastrointestinal motility is the contraction of the smootm muscles that is located in the gastrointestinal tract.The gastrointestinal tract includes mouth,esophagus,stomach,small intestine and large intestine. All these parts are seperated by muscles known as sphincters that helps to regulate the movement of food that we eat and to move the residues of food from one part to another part.All these parts has diffrent roles in the digestion process so their motility is diffrent from each other.The mouth and esophagus motility has three phases voluntary phase,pharyngeal phase and esophagal phase.In the voluntary phase food is pushed towards the posterior part of the mouth and it moves to oropharynx.In the next phase this food stimulates receptors and then food goes to pharynx.The pharyngeal muscles contracts and then forces food through pharynx and food is pushed to esophagus.In esophageal phase muscle contractions called peristalsis occurs in esophagal walls and also food in esophagus can stimulate enteric plexus that controls the local reflexes.These reflexes pass through vagus nerve thus the muscles in esophagus stimulates peristaltic contraction that helps move food to stomach.The gastro mobility in stomach include both peristalsis and segmentation which is mixing the food.The contractions of muscles starts near lower esophageal sphincter and then towards pyloric sphincter.Thus the food is mixed with stomach secretions to form chyme.Gastric mobility of small intestine includes segmental contractions and peristaltic waves that is regulated by local reflexex.Mobility of large intestine has strong peristaltic contractions that leads to sudden distension of rectum that triggers defecation.All these Gastric mobility is regulated by the reflexes called long reflexes and short reflexex.The gastrointestinal peptides stimulate and inhibits the mobility.The peptides includes cholecystokinin,secretin,motilin and glucagon-like peptide 1.

After the food inside the stomach forms chyme , it is evacuated to the intestine.In the process of gastric emptying the chyme passes through pylorus and allows evacuation as a result of the gastro-duodenal gradient pressure.The amount of chyme that is pushed out depends on the ingested volume ,solubility ,gastric secretion and mixing of food.The emptying is regulated by the physical and chemical nature of the food and is achieved through several neuro hormonal control mechanism. There are inhibitory and excitory motor circuits that regulates gastric emptying with their regulatory neurons located in solitary tract nucleus.In this mechanism stomach contractions that originates in antrum prevents rapid emptying.Also acid in deodenum stimulates secretin hormone that inhibits gastro motility.Fats contained in deodenum secretes cholecystokinin and lucagon-like peptide 1.Finally hypertonicicity in deodenum can inhibit gastric emptying.