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Transcript of STOMACH
It is an enlarged segment of the digestive tract in the left superior part of the abdomen.
It functions as the storage and mixing chamber for ingested food.
Anatomy of the Stomach
Cardiac Region – region of the stomach around the gastrophageal opening.
Gastroesophageal Opening – opening from the esophagus to the stomach.
Body – largest part of the stomach.
Fundus – most superior part of the stomach.
Pyloric sphincter – a relatively thick ring of smooth muscle that surrounds the pyloric opening.
Pyloric Opening – opening from the stomach into the small intestine.
Histology of the Stomach
Outer longitudinal layer
Middle circular layer
These muscular layers of the stomach produce a churning action in the stomach that is important to the digestive process.
Rugae – large folds of the mucosa.
Gastric pits – formed by the mucosal surface.
EPITHELIAL CELLS OF THE STOMACH CAN BE DIVIDED INTO FIVE GROUPS:
Surface Mucous Cells – inner surface of the stomach and lining of the gastric pits.
Mucous Neck Cells – produce mucus
Parietal Cells – produce hydrochloric aid and intrinsic factor
Endocrine Cells – produce regulatory chemicals
Chief Cells – produce pepsinogen
Secretions of the Stomach
Hydrochloric Acid – produces a pH of about 2.0 in the stomach. It kills microorganisms and activates pepsin.
Pepsin – exhibits optimum enzymatic activity at a pH of about 2.0. It starts protein digestion.
Mucus – It lubricates and protects the epithelial cells of the stomach wall from the damaging effect of the acidic chyme and pepsin.
Intrinsic Factor – It aids in Vitamin B12 absorption.
Regulation of Stomach Secretions
1.) The taste, smell, or thought of food or tactile sensations of food in the mouth stimulate the medulla oblongata (green arrow).
2.) Vagus nerves carry parasympathetic action potentials to the stomach (pink arrow), where enteric plexus neurons are activated.
3.) Postganglionic neurons stimulates secretion by parietal and chiel cells and stimulates gastrin and histamine secretion by endocrine cells.
4.) Gastrin is carried through the circulation back to the stomach (purple arrow), where, long wo
1.) Distention of the stomach stimulates mechanoreceptors (stretch receptors) and activates a parasympathetic reflex. Action potentials generated by the mechanoreceptors are carried by the vagus nerves to the medulla oblongata.
2.) The medulla oblongata increases action potentials in the vagus nerves that stimulates secretions by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells.
3.) Distention of the stomach also activates local reflexes that increase stomach secretions.
4.) Gastrin is carried through the circulation back to the stomach (purple arrow), where, along with histamine, it stimulates secretion.
1.) Chyme in the duodenum with a pH less than 2 or containing fat digestion products (lipids) inhibits gastric secretions by three mechanisms (2-4).
2.) Chemoreceptors in the duodenum are stimulated by H+ (low pH) or lipids. Action potentials generated by the chemoreceptors are carried by the vagus nerves to the medulla oblongata (green arrow), where they inhibit parasympathetic action potentials (pink arrow), thereby decreasing gastric secretions.
3.) Local reflexes activated by H+ or lipids also inhibit gastric secretion (orange arrows).
4.) Secretin and cholecystokinin produced by the duodenum (brown arrows) decrease gastric secretions in the stomach.
Movement in the Stomach
1.) A mixing wave initiated in the body of the stomach progresses toward the pyloric sphincter.
2.) The more fluid part of the chyme is pushed toward the pyloric sphincter, whereas the more solid center of the chyme squeezes past the peristaltic constrictions back toward the body of the stomach.
3.) Peristaltic waves move in the same direction and in the same way as the mixing waves but are stronger.
4.) Again, the more fluid part of the chyme is pushed toward the pyloric region, whereas the more solid center of the chyme squeezes past the peristaltic constriction back toward the body of the stomach.
5.) Peristaltic contractions force a few millimeters of the most fluid chyme through the pyloric opening into the duodenum. Most of the chyme, including the more solid portion, is forced back toward the body of the stomach for further mixing.