Gastric Secretion Flashcards
What are the three main functional parts of the stomach?
Fundus, body and antrum
What is the fundus of the stomach responsible for?
Storage
What are the functions of the body of the stomach?
Storage Mucous production HCl production Pepsinogen production Production of intrinsic factor
What are the functions of the antrum of the stomach?
Mixing and grinding of the stomach contents
Production of gastrin
What feature of the antrum aids the mixing and grinding of the stomach contents?
Very thick muscularis externae
Where is gastrin released and what does it do?
Released in the antrum, gastro-intestinal hormone which is secreted into stomach lumen, taken into circulation then returned to stimulate the stomach cells
What three mechanisms control gastric acid secretion?
Neurocrine - vagus nerve and local reflexes
Endocrine - gastrin
Paracrine - histamine
What is the first thing to prepare the stomach for digestion and what does this cause?
Precursors to eating - sight, smell and taste of food
Causes stomach to create acid which will instantly sterilise any bacteria ingested
What three things are stimulated by the vagus nerve or by gastrin in the cephalic phase to trigger acid production?
Stomach
G cells
ECL cells
When does the gastric phase occur?
Once there is a physical presence of food in the stomach
Distension of the stomach (gastric phase) triggers long reflexes from the _ and short reflexes from the _
Vagus nerve
Enteric reflexes
Vagus nerve and enteric reflexes trigger the release of
ACh
Peptides in the lumen stimulate
G cells which release gastrin
Gastrin and ACh can also stimulate the ECL cells which release
histamine
What will inhibit gastric acid secretion in the cephalic phase?
Absence of stimulus i.e. stop eating
What will inhibit gastric acid secretion in the gastric phase?
H ion increases, pH decreases leading to decreased gastrin release as environment is acidic enough
Pancreatic enzymes are extremely sensitive to
acid/low pH
Acid in the duodenum triggers
the enterogastric reflex and secretin release from the surface of the duodenum
Secretin triggers the release of
bicarbonate
Secretin and bicarbonate will cause
reduction in gastric secretion and therefore reduce the effect of gastrin stimulation on the parietal cells
Fat in the duodenum causes the release of _ which causes
gastric inhibitory peptide
causes reduced gastric secretion and reduced parietal HCl secretion
The intestinal phase occurs when
signals are sent that the stomach is emptying its contents
The intestinal phase reduces
acid damage to the duodenum
What is pepsinogen?
The zymogen of pepsin
What is a zymogen?
An inactive precursor of an enzyme
When is pepsinogen converted to pepsin?
When the pH is below 3
When are pepsins inactivated?
At neutral pH
Gastric motility causes the
mixing of the stomach contents, contraction of pyloric sphincter and further mixing
What is the function of the pyloric sphincter?
Controls passage of stomach contents into the duodenum
What are responsible for gastric motility?
Peristaltic waves
Where do peristaltic waves originate?
Oesophagus
Why are more powerful contractions possible once the peristaltic wave reaches the antrum and pyloric sphincter?
As the muscle here is thicker and more powerful
Does gastrin increase or decrease contraction in the stomach?
Increase
How is the stomach emptied?
Gradually
The presence of what in the duodenum will inhibit gastric motility?
Fat
Acid
Amino acids
Hypertonicity
What is the only essential, non-compensated function of the stomach?
Releasing intrinsic factor to form a complex with vitamin B12, allowing it to be absorbed from the ileum
What will a defect in intrinsic factor lead to?
Pernicious anaemia
What cells produce gastric mucous?
Surface epithelial cells and mucous neck cells
What role does gastric mucous have?
Cytoprotective role
What is the function of the high bicarbonate content of gastric mucous?
Neutralises the pH of gastric acid, completely denaturing pepsin and stopping the corrosive acid from reaching the cells below the mucous layer
