Functions Of The Stomach Flashcards
What are the basic functions of the stomach?
Short term storage of food
Mechanical and chemical disruption of food
Continue digestion (proteins mainly)
Disinfect
What epithelium lines the stomach?
Simple columnar
What are rugae?
Fold in the mucosa and submucosa
Allow distension of the stomach
How many layers of smooth muscle are there in the stomach?
3
Why do we want to grind our food?
Increase the surface area for enzymes to work on
Describe receptive relaxation of the stomach
Vagus nerve mediated
Allows food to enter the stomach without raising the intragastric pressure too much
Prevents reflux
Distension of rugae
Why do we have acidic conditions in the stomach?
Help to unravel protein
Activates proteases
Disinfects stomach contents
What do the parietal cells secrete?
HCl and intrinsic factor
What do the G cells secrete?
Gastrin
What do the enterochromaffin like cells (ECL) secrete?
Histamine
What do the chief cells of the stomach secrete?
Pepsinogen
What do the D cells secrete?
Somatostatin
What do the mucous cells in the stomach secrete?
Mucus
What is the predominant secretion in the cardia of the stomach?
Mucus
What is secreted in the body and fundus of the stomach?
Mucus, HCl, pepsinogen
What is secreted at the pylorus of the stomach?
Gastrin, somatostatin
The parietal cells are stimulated to release HCl via …
Gastrin
Histamine
ACh
How are parietal cells adapted for acid release?
Have many invaginations of the cell membrane to increase the surface area for acid release
What receptors are present on the parietal cells and what binds to them?
CCK receptor - gastrin binds
H2 receptor - histamine
Muscarinic receptor - ACh
What stimulates gastrin secretion?
Peptides/amino acids in the stomach lumen
Vagal stimulation
Where are the G cells located?
Antrum
What factors inhibit HCl production?
Inhibition of G cells - less gastrin
Food leaving the stomach, decrease in pH, activates D cells - somatostatin which inhibits G cells
Stomach distension reduces - reduced vagal stimulation
Somatostatin also prevents the production of histamine
Describe HCl production
Water split inside the parietal cells (OH- and H+)
H+ moved into stomach lumen
Cl- moved into stomach lumen (the 2 combine)
CO2 combines with the OH- forming bicarbonate which is moved into the blood stream creating the alkaline tide during acid production
Describe the antiporter present on the basolateral surface of parietal cells
HCO3- moves into blood (out of cell)
Cl- moves into cell (out of blood)
How do we scientifically write the proton pump?
H+/K+/ATPase
How does the proton pump work?
Uses ATP to pump H+ into stomach lumen against huge conc gradient
In exchange for a K+ ion
What are the 3 phases of digestion?
Cephalic
Gastric
Intestinal
Describe the cephalic phase of digestion
Before things arrive in the stomach 30% total HCl secreted PNS stimuli - direct stimulation of parietal and G cells via vagus nerve Anticipating food Also increases gastric motility slightly
Describe the gastric phase of digestion
Food actually in the stomach
60% of total HCl secreted in this stage
Distension stimulates vagus -> parietal and G cells
Presence of amino acids -> G cells
Food acts as a buffer
Enteric NS and gastrin cause strong muscular contractions - acceleration of food towards pyloric sphincter
Describe the intestinal phase of digestion
10% of HCl production done in this phase
Chyme initially stimulates HCl secretion
Soon overtaken by inhibiton of G cells
Presence of lipids activates enterogastric reflex - reduced vagal stimulation - reduced secretions
Chyme stimulates CCK and secretin which help suppress secretions
Name some factors that protect the stomach
Mucus
Bicarbonate
Rapid turnover of epithelial cells
Why do we need the thick alkaline layer at the epithelium in the stomach?
Higher pH so that proteases are not activated near the stomach surface
Why are NSAIDs bad for the stomach?
Reduce synthesis of prostaglandins
Decrease the mucosal blood flow
Decreased nutrients to epithelium
Breaching stomach defences
How does alcohol breach the stomach defences?
Dissolves the mucus layer
What is the most effective way to stop acid production?
PPIs
Eg. Omeprazole, lansoprazole
Give examples of H2 antagonists
Cimetidine
Ranitidine
