7) Functions of the Stomach Flashcards
What are the basic functions of the stomach (4)?
Stores food
Disrupts food (contractions)
Continues digestion
Disinfects food
What is the first section of the stomach called?
Cardia, where oesophagus enters
What are the other sections of the stomach (top to bottom)?
Fundus, body, antrum, pylorus (+sphincter)
What is the change in epithelium at the cardia?
Transition of stratified squamous to columnar (secretion)
Describe the muscosa of the stomach:
In folds (rugae), to allow distension by flattening of these folds
What are gastric pits?
‘Little holes’ on stomach surface
These pits have gastric glands (specialised cells) at the bottom
What causes the movement of substances from the cardia to pylorus?
Upper stomach has basal tones created by sustained contractions which force flow down funnel shaped stomach
How many muscle layers does the stomach have?
3 - oblique, circular and outer longitudinal
What is receptive relaxation?
As food travels down oesophagus, vagus nerve triggers relaxation of orad stomach wall (flattening of rugae)
What does receptive relaxation stop?
Stops rises in intra-gastric pressure
Prevents reflux
What are the functions of stomach acid?
Helps unravel proteins - larger SA
Activates proteases - pepsin
Disinfection
What do parietal cells secrete?
HCl
Intrinsic factor
What do G cells secrete?
Gastrin
What do enterochromaffin like cells secrete?
Histamine
What do chief cells secrete?
Pepsinogen
What do D cells secrete?
Somatostatin
What do mucous cells (surface + neck) secret?
Mucus
What are the predominant secretions of the cardia?
Mucus
What are the main secretions of the fundus and body?
Mucus, HCl, pepsinogen
What are the main secretions of the pylorus?
Gastrin, somatostatin
What stimulates secretion of stomach acid?
Gastrin, histamine and ACh
What feature of the parietal cell allows increased acid secretion?
Invaginations on cell surface (canaliculi) increase SA for secretion
What stimulates gastrin secretion?
Peptides/AAs in the stomach lumen
Vagus stimulation - ACh, gastrin releasing peptide
What inhibits acid production?
Low stomach pH - food acts as buffer
Low pH also activates D cells –> somatostatin which inhibits G and ECL cells
Reduction in stomach distension reduces vagal activity
Describe the formation of HCl:
Water split to OH- and H+
H+ and Cl- into stomach lumen to form HCl
Uses H+/K+ ATPase
What happens to the OH- produced in HCl formation?
Combines with CO2 to form HCO3-
This moves into bloodstream, alkaline tide (HCO3-/Cl- antiporter)
What are the 3 phases of digestion?
Cephalic
Gastric
Intestinal
What occurs in the cephalic phase of digestion?
Vagus nerve stimulates parietal and G cells in response to smelling, tasting, chewing and swallowing
Increase in gastric motility
30% of HCl
What occurs in the gastric phase of digestion?
Distension of stomach stimulates vagus (parietal and G cells)
Presence of AA/peptides stimulates G cells
Food acts as buffer so no inhibition of gastrin
Enteric NS and gastrin cause strong SM contractions
What occurs in the intestinal phase of digestion?
Inhibition of G cells due to presence of lipids - enterogastric reflex, reduced vagal
Chyme stimulates CCK and secretin
What defences does stomach have against acid?
Mucus and HCO3- - form thick alkaline viscous layer over epithelium
High turnover of epithelial cells
Prostaglandins maintain mucosal blood flow
What can breach stomach defences?
Alcohol - dissolves mucus layer
Helicobacter pylori - inflamm of stomach lining
NSAIDS - inhibit prostaglandins
What can breach of stomach defence lead to?
Gastritis
Ulceration
Reflux disease
What pharmacological interventions can be used to reduce acid secretion?
H2 blockers - cimetidine
Proton pump inhibitors - omeprazole
What slows gastric emptying?
Fat, low pH and hypertonicity in duodenum
