Stomach Flashcards
Which structure related to the stomach can limit the spread of infection?
Greater omentum as it can adhere to infected sites
What part of the stomach will you likely be able to see on a radiograph when the patient is standing?
Fundus because it is filled with air
Where is the lesser omentum?
Between liver and stomach
What is special about the splenic artery?
Tortuous so can stretch
What does free border of lesser omentum become?
Hepatoduodenal ligament
What is the pringle manoeuvre?
Clamping of hepatoduodenal ligement during surgery to prevent excessive bleeding from liver
What are the 3 phases of gastric motility?
Receptive relaxation
Mixing
Emptying
Which 2 electrical modalities contribute to the coordinated contraction of smooth muscle in the stomach?
Slow waves
Action potentials
Which phase of gastric motility occurs in the orad region?
Receptive relaxation
How does the stomach expand to accommodate food?
Unfolding of rugae
Describe the mixing process in the stomach
Peristaltic waves move food towards antrum
When approaching antrum, contraction force increases and pyloric sphincter shuts
This forces most of the food back into the stomach - retropulsion
List 5 functions of the stomach
Storage of food Minimise ingestion of bacteria Dissolve and partly digest macromolecules Regulate rate of gastric emptying Secrete intrinsic factor
Which reflex is activated when food enters digestive system?
Vagovagal
List 3 things which stimulate acid production in the stomach
ACh
Histamine
Gastrin
List 3 things which inhibit gastric acid secretion
Somatostatin
Prostaglandin
Enteric hormones
What disruption of acid base balance can excessive vomiting cause?
Metabolic alkalosis
What 2 problems can be caused by hypochlorhydia?
Increased vulnerability to GI bacterial infection
Impaired ability to digest and absorb certain nutrients and B vitamins
What does carbonic anhydrase do?
Catalyses reaction producing H+ and HCO3 from H2O and CO2
Give 2 functions of the pyloric sphincter
Prevent regurgitation
Allow regulated emptying of stomach
What effect does CCK have on the pyloric sphincter?
Constriction
How is gastric emptying regulated?
By duodenal contents. Receptors on duodenal and jejunal mucosa detect acidity, osmotic pressure, fats, amino acids, peptides etc.
A high fat meal, high acidity or very hypertonic would all decrease the rate of gastric emptying
What needs to contract to bring about emptying of the stomach?
Contraction of stomach, pylorus and proximal small intestine
Relaxation of pyloric sphincter
Name the 4 parts of the stomach
Fundus
Body
Pyloric antrum
Pyloric canal
What is a mesentery?
Mesenteries are double-layered folds of peritoneum attaching the gut tube to the body wall
What does the free edge of the lesser omentum contain?
Contains common bile duct, hepatic artery, portal vein
What does the greater omentum contain?
Blood vessels and fat
Describe the blood supply to the stomach
Coeliac trunk derived
Left and right gastric form anastamotic loop which supplies lesser curvature
Splenic artery branches to the short gastric and left gastro-epiploic/omental which forms anastamotic loop on greater curvature with right gastro-epiploic/omental which comes from gastroduodenal which also branches to superior pacreaticoduodenal
What does gastric motility allow the stomach to do?
Serve as reservoir for large volume
Fragment food into smaller particles and mix it with gastric secretions
Empty gastric contents at a controlled rate
What is the volume of the empty stomach?
50ml
Describe receptive relaxation
Food is swallowed, smooth muscle in stomach wall orad region relaxes
Enables stomach to increase volume to 1.5L with little increase in pressure
Which nerve mediates receptive relaxation?
Vagus coordinating with enteric nerve plexuses
Enteric nerves release NO and serotonin to mediate smooth muscle relaxation
What is the predominant motor activity of the orad region?
Accommodation of ingested food
Muscle layers are thin so contractions here are weak
What is the basic electric rhythm of the GI tract?
Smooth muscle cells undergo spontaneous cycles of depolarisation and repolarisation
What are slow waves?
Fluctuations in membrane potential spreading from adjacent sections of muscle
Gastric slow waves at 3/min
Rhythm generated in pacemaker zone
Coordinate contractions by controlling appearance of action potentials
What is the pyloric sphincter?
Ring of smooth muscle and connective tissue between gastric antrum and duodenum
Which hormones cause constriction of the pyloric sphincter?
CCK, gastrin, GIP, secretin
What effect do enteric hormones have on gastric emptying?
Inhibit antral contractions
Constriction of pyloric sphincter
Decrease gastric emptying
How much gastric juice is released per day?
3L
What are the main components of gastric juice?
Hydrochloric acid
Mucus
Enzymes - pepsinogens, gastric lipase
Intrinsic factor
What are the 5 cell types in gastric pits?
Surface mucus cells Mucus neck cells Parietal cells - HCl and intrinsic factor Chief cells - pepsinogen G cells - gastrin
Where are parietal cells located?
Proximal 80% of stomach, oxyntic gland area
Where are G cells located?
Antrum, pyloric gland area
What are gastric hormones?
Gastrin
Histamine
Somatostatin
What is gastrin?
Principal hormone secreted from gastric epithelium
Polypeptide secreted by G cells
Stimulates acid secretion, pepsinogens, mucus, HCO3
Stimulates gastric motility
Inhibits gastric emptying
Stimulates pancreatic secretions, insulin release, intestinal motility
What effect does histamine have on GI tract?
Paracrine agent
Secreted by enterochromaffin like cells (ECL cells) close to parietal cells
Stimulation of acid secretion
Increased local blood flow
What effects does somatostatin have on GI tract?
Polypeptide synthesised by D cells in antrum and body of stomach
Inhibits gastrin release
Inhibits acid secretion
What is special about the shape of parietal cells?
Truncated pyramidal, apex oriented towards gastric lumen
Extensive invaginations of luminal membranes forming canaliculi lined with ion pumps
High mitochondrial content
How is gastric acid produced?
H+ and HCO3 produced from H20 and CO2
H+ secreted into lumen by H/K ATPase
HCO3 moves out of basolateral membrane via antiport with Cl-
Cl- diffuses passively into lumen via Cl channel
How does prostaglandin inhibit gastric acid secretion?
Blocks activity of histamine on parietal cells
How does somatostatin inhibit gastric acid secretion?
Acts on ECL cell to reduce histamine release
Acts on parietal cell to block effects of gastrin
What is mucus?
Mixture of glycoproteins and glycopolysaccharides
Forms a viscous gel on luminal surface with alkaline secretions trapped in it
Gastric mucosal barrier to protect against acid, enzymes and mechanical damage
Allows cells to be kept at near neutral pH despite low pH of stomach
Describe renewal of the gastric mucosal barrier
Local irritation to mucosa stimulates production of prostaglandins which increase mucus and HCO3 production and inhibit acid secretion. Also promote healing
Stimuli of acid secretion also promote mucus and HCO3 production
Why can excessive use of NSAIDs cause stomach damage?
Blocks production of prostaglandins which act to reduce acid secretion, increase mucus and HCO3 production and promote healing
What are antacids?
Base, counteracts stomach acidity by buffering, so raise pH
What are alginates?
Anionic polysaccharides that form a viscous gel on binding water
Increase viscosity of stomach contents so protect from acid reflux
Gel raft floats on stomach contents
What is Misoprostol?
Stable analogue of prostaglandin 1
Inhibits acid secretion and mucosal blood flow
Augments secretion of mucus and HCO3
Given to prevent gastric damage that can occur with chronic use of NSAIDs
Give examples of histamine receptor antagonists
Cimetidine
Ranitidine
Famotidine
Nizatidine
How effective are histamine receptor antagonists at reducing acid secretion?
Decrease basal and stimulated secretion by 90%
In which patients should caution be used with H2 antagonists?
Hepatic and renal failure
Pregnancy and breast feeding
Give examples of PPIs
Omeprazole Lansoprazole Esomeprazole Pantoprazole Rabeprazole
What are advantages of PPIs over H2 antagonists?
Inactive at neutral pH so activated where required in acidic stomach
Accumulate in canaliculi of parietal cells
What is pepsin?
Secreted as Pepsinogen by chief cells Exposure to low pH causes conversion to pepsin It's secretion parallels acid secretion Active only at low pH Accelerates protein digestion
What is intrinsic factor?
Glycoprotein
Secreted by parietal cells
Essential for Vit B12 absorption in small intestine
