Flashcards in Physiology and Pharmacology of Gastric Motility and Secretion Deck (54)
What is stomach relaxation driven by?
What is the starting point for digestion of proteins?
HCl and pepsin
What is produced by the stomach?
What are the rugae?
folds in the empty stomach
What is the fundus?
top of stomach, gas pocket, usually no food
What is the antrum?
next to duodenum - thick sm. muscle for contraction
How is food mixed in the stomach?
peristalic wave forces chyme down and back against pyloric sphincter which causes retropulsion
What size of food does the pyloric sphincter let through?
2mm or less
What governs the strength of the antral wave?
gastric factors and duodenal factors
What are the gastric factors mediating the antral wave?
rate of emptying is proportional to volume of chyme in stomach
distension increases motility due to stretch of smooth muscle, stimulation of intrinsic nerve plexus and increased vagal nerve activity and gastrin increase
consistency of chyme
What are the duodenal factors mediating the antral wave?
must be ready to recieve chyme and can delay emptying
How does the duodenum delay emptying of the stomach?
neuronal response - enterogastric reflex decreases antral peristalic wave from intrinsic nerve plexuses and ANS
hormonal response - release of secretin and CCK
What are the stimuli that drive the neuronal and hormonal responses of the duodenum?
fat - particularly potent as time required for digestion
acid - time needed for neutralisation by HCO3
hypertonicity - products of carbohydrate/ protein digestion are osmotically active and draw water into the sm. intestine
Where do secretions from the gastric glands come from?
Pyloric Gland Area
What is produced by the oxyntic mucosa?
enterochromaffin cells - histamine - paracrine
chief cells - pepsinogen
parietal cell - HCl, Intrinsic factor
What is produced by the pyloric gland area?
D cell - somatostatin - endocrine
G cell - gastrin - endocrine
What is the function of HCl?
activates pepsinogen -> pepsin
kills most micro-organisms ingested
What is the function of pepsinogen?
inactive precursor of peptidase - pepsin
pepsin is autocatalytic once formed
What is the function of Intrinsic Factor?
binds vitB12 - allowing absorption in the terminal ileum - essential as only found in stomach
What is the function of histamine?
stimulates HCl secretion
What is the function of mucus?
protects stomach wall
What is the function of gastrin?
stimulates HCl secretions
What is the function somatostatin?
inhibits HCl secretion
What are the processes involved with secretion of HCl?
Conversion of CO2 and H20 to HCO3 + H
HCO3 exiting the cell and bringing Cl into the cell
H being extruded into the cannaliculus
Cl being extruded into the cannaliculus
What converts CO2 and H20 to H2CO3?
What takes HCO3 out of the cell?
How is H taken into the cannaliculus?
via H-K ATPase
Which cell produces HCl?
The parietal cell
How is H+ increased by the parasympathetic nervous system?
ACh stimulates M3 on parietal cells and M1 on ECL cells
Gastrin activates CCK2Rs on parietal and ECL cells
Hitamine generated from M1 and CCK activates H2R on parietal