GI physiology of mouth, esophagus and stomach

Chewing motility pattern function

function: mechanical digestion, mixing food with saliva
voluntary (taken over by reflexes)

secretion rates of the mouth

basal/resting and stimulated

composition of saliva 

mucus, electrolyte fluid (contains bicarbonate), digestive enzymes 

regulation of saliva production by CNS 

PNS = watery 
SNS = viscous

swallowing motility pattern function

function: rapid transfer of food from mouth to stomach and preventing food going the wrong way
starts voluntary, continues under reflexes

what motility patterns comprise swallowing?

relaxing of upper and lower esophageal sphincters 
peristalsis 

what prevents food going the wrong way during swallowing?

uvula and soft palate block nasopharynx
epiglottis flaps down to cover trachea

function of relaxation in the stomach

to increase stomach volume with minimal change in lumen pressure 
ensures stomach is always lower pressure than esophagus so food moves in one direction

two types of relaxation

receptive and accomodation

what is retropulsion?

peristalsis grinds chyme against contracted pyloric sphincter to finish mechanical digestion 

what is gastric emptying?

pyloric sphincter relaxes to allow fully digested chyme to pass through to duodenum
regulated by feedback from duondenum

regulation of gastric emptying

feedback from duodenum to match secretion of chyme with pancreatic and liver secretions

secretion of stomach

goblet cells - mucus (with water and bicarbonate) secreted onto stomach epithelial cells for protection
chief cells - pepsinogen
parietal cells - HCl acid
G cells (gastric enteroendocrine)- gastrin

formation of HCl acid by parietal cells (steps)

H+ made inside the cell 
H+ secreted against conc gradient 
Cl- moved into then out of cell
H+ and Cl- react to form HCl in lumen 

phases of gastric regulation

cephalic → gastric → intestinal

cephalic phase summary (function, pathway, response)

prepares stomach for arrival of food via CNS pathway
20% of gastric secretion and no change in motility

gastric phase summary (function, pathway, response)

stomach is carrying out mechanical and chemical digestion via. local/short reflex
70% of gastric secretion and large increase in motility

intestinal phase summary (function, pathway, response)

stomach is inhibited while SI and accessory organs are stimulated via. long reflex and hormonal pathways 
10% of gastric secretion and decrease in motility

steps of cephalic phase

see/smell food → CNS pathway → submucosal plexus → increased secretion

steps of gastric phase

food arrives → receptors → ENS (submucosal and myenteric plexus) → increased secretion and increased motility
G cells stimulated by secretion also increase motility

steps of intestinal phase (receptors)

chyme arrives in duodenum → receptors → CNS → SNS → ENS → decreased secretion and motility

steps of intestinal phase (hormones)

chyme arrives in duodenum → enteroendocrine cells secrete CCK and secretin → decreased gastric secretion → less gastrin → decreased motility