Regulation of Gastric Secretion, Motility, and Emptying

1. Regulation of Gastric Secretion ("Gastric Juice")
1. cephalic (reflex) phase
• sight, aroma, taste, thought -----> hypothalamus gustatory centers -----> vagal nuclei of medulla -----> vagus nerve (parasympathetic) -----> increased gastric secretion
2. gastric phase
• food reaches the stomach --------> neural mechanism hormonal mechanism distention & low acidity ---> digested proteins ---> vagal afferents to medulla ---> increase in pH ---> vagal efferents to stomach ---> gastrin released ---> parasympathetic ACh release ---> enzymes & HCl released --> increased gastric secretion
• control of HCl secreting parietal cells
• gastrin, histamine, & ACh increase the release of HCl from parietal cells
• H+ comes from carbonic acid release
3. intestinal phase
• excitatory phase inhibitory phase --> chyme enters the duodenum -> inhibition of vagal nuclei ---> release of intestinal gastrin -> inhibition of local reflexes
• continued gastric secretion activation of sympathetics --- > release of inhibitory hormones: (secretin, cholecystokinin CCK, gastric inhibitory peptide GIP)
2. Gastric Motility and Emptying
1. receptive relaxation - trilayer of muscles in wall of the stomach relax to allow filling to occur
2. plasticity - smooth muscle tension specially regulated to prevent regurgitation of food
3. basic electrical rhythm - pacemaker cells of longitudnal muscle allow rhythmic contractions
4. emptying to duodenum - regulated by amount and type of chyme entering into the duodenum; faster with high carbo, slower with higher fats
5. vomiting (emesis) - irritants activate neurons which stimulate the "emetic center" of medulla

Category: Physiology Notes