Lecture 8 Flashcards
Where does the stomach begin?
At the gastroesophageal junction where the oesophagus ends.
What is the superior part of the stomach?
Fundus. It is the curvature at the top of the stomach. Acts as a chamber.
What is medial to the gastroesophageal junction?
Cardia.
What makes up majority of the stomach?
The body.
What is towards the distal end of the stomach?
The antrum. The antrum feeds into the pylorus (sphincter).
What does the pylorus control?
The entry of food into the duodenum.
What does the greater curvature consist of?
Rural folds. They aid the digestion of gastric contents.
What is the incisura?
The angle that connects the lesser curvature to the antrum.
What are the major functions of the stomach?
- reservoir for food.
- Digests food - has to do this to allow food to become particular consistency before entering the duodenum. Needs to enter small intestine as chyme.
- Antrum mixes and grinds up the food.
- Pylorus regulates the size of particles, before they move into the small intestine.
- Gastric acid secretion - 1.5L per day.
- Secretes: mucus, bicarbonate, intrinsic factor, pepsinogen, and prostaglandins.
What happens in gastric motility?
The funds acts as a food store, the body and antrum mix the food and the pylorus contracts to limit exit of chyme.
What are the exact steps in the motility of the stomach?
- Relaxation of fundus (vasovagal reflex). When meal enters it, mediated by the vagus nerve. Vagus nerve causes reflex which tells funds to relax, and food is stored.
- Contraction of body and antrum. Allows food to be moved to distal part of the stomach.
- Pylorus contracts. Needs to remain shut during physical digestion of the food.
- Mixing by retropulsion. Allowing food to digest into smaller particles.
Normal function requires?
- Intact antrum - as the antrum does a lot of the mixing.
- Intact pylorus - things won’t be held in the stomach with digestion if not intact.
- Intact duodenum - controls the release of chyme into the small intestine for alter digestion by the pancreas.
- Normal vagus nerve.
- Normal hormone function.
What is abnormal gastric emptying?
Either rapid or delayed.
What causes rapid gastric emptying?
People who have had gastric-surgery. People have had their antrum removed and pylorus, they can develop “dumping syndrome”.
What is the “dumping syndrome”?
Rapid entry of food from the stomach into the small intestine.
What are the symptoms for “dumping syndrome”?
Nausea.
Vomiting.
Cramping.
Diarrhoea.
What causes “dumping syndrome”?
No antrum to mix up the food, and no pylorus to control the exit of food. So food is not completely digested [hyperosmolar chyme]. The large particles act as an osmotic pressure. They draw fluid into the small intestine and it causes the stomach to distend.
What does the hyperosmolar chyme cause?
Rapid fluid shift into the gut, causing intestinal distension = pain. Diarrhoea due to osmotic effect. Can cause committing as well.
What causes delayed gastric emptying?
Diabetic gastroparesis, which is caused by an autonomic neuropathy.
What is gastric secretion common to?
All mammals.
What is the main role of gastric acid?
It sterilises the food. The stomach environment is hostile to most bacteria except for Helicobacter pylori.
What else can gastric acid do?
It can help in absorption of iron and B12.
What happens when people have low or absent gastric acid?
Achlorhydia. It is common with people who have pernicious anaemia.
How is acid secreted
in the stomach?
Parietal cells are located in the body of the stomach. They secrete acid.
What causes parietal cells to secrete gastric acid?
They have proton pumps on the parietal cells which secrete approximately 2L a day of HCl acid.
Describe the H+/K+-ATPase Pump on the parietal cell?
It’s known as a proton pump and it requires ATP as energy for reaction.
What does the Parietal pump do?
It actively pumps hydrogen ions out of the cell into the stomach:
H2O + CO2 H+ + HCO3-. The reaction is catalysed by carbonic anhydrase.
K+ then enters the cell and HCO2- is transported out of the cell into the bloodstream.
Why is ATP required to drive the reaction?
It shifts hydrogen against the concentration gradient. Cell has to actively increase the concentration, by pumping the ions from a low concentration to a high concentration. The [H+] inside the cell = 4x10^8 M; [H+] outside the cell = 0.5M. Thus the cell needs ATP/energy.
What happens when the parietal cells are active (secreting)?
The tubulovesicles fuse with the canaliculus, increased surface area and numbers of H+/K+ - ATPase increases acid secretion into the lumen of the gut. Acid secretion is against a 3 million fold concentration gradient.
How does the stomach protect itself?
It secretes a layer of mucus that protects the stomach form exposure to the acid. It secretes bicarbonate to the epithelium to protect it from the acidic environment.
Why is the protection important?
It is the basis of why peptic ulcers form. If the layer of protection is destroyed, then ulceration occurs due to acidic environment.
Define neurotransmitter?
Molecule that transmits a signal from one neurone to another.