Gastric secretion Flashcards
What is the fundus?
Upper part forming the majority of the stomach
What is the structure of the fundus?
Thinner musculature
Pleats on surface allow for increase in volume
What is the function of the fundus?
Storage
What is the function of the body of the stomach?
Storage Mucus HCl production for sterilisation Pepsinogen production Intrinsic factor production
What is the function of the antrum?
Mixing and grinding
Gastrin production
What is the cellular composition of gastric glands?
Mucous neck cells
Chief cells
Parietal cells
What is the function of mucous neck cells?
Secrete mucus
What are mucous neck cells?
Immature surface cells
What is the function of chief cells?
Secrete pepsinogen
What is the function of parietal cells?
Secrete HCl and intrinsic factor
How does water pass from the stomach lumen to the bloodstream?
Passes through tight junctions between the parietal cells
What happens to CO2 in the stomach lumen?
Passiveley enters the parietal epithelium and binds with H20 to form H2CO3
What happens to H2CO3 in the parietal epithelium?
Splits into HCO3 and H
H is transported into lumen as K is transported in
HCO3 transported into blood as Cl is transported in
What happens to H in the stomach lumen?
Binds with Cl to form HCl and lower the stomach pH
What secretions have an effect on the stomach?
Gastrin
Histamine
Acetylcholine
Prostaglandins
What does gastrin do?
Activates a receptor on the basolateral membrane causing a rise in intracellular Ca, that tells protein kinases to pump more H across the apical membrane, decreasing the pH of the stomach lumen
What does histamine do?
Stimulated the H2 receptor inducing uptake of CO2 and H2O which in turn decrease the pH of the stomach lumen
What does acetylcholine do?
Cause increase in intracellular Ca, that tells protein kinases to pump more H across the apical membrane, decreasing the pH of the stomach lumen
What do prostaglandins do?
Couple themselves to inhibited G proteins and reduce protein kinase activity to even out the pH of the stomach lumen
What is the main release of acetylcholine and what does it act on for the stomach?
Vagus nerve
Muscarinic cholinergic
What are the 3 types of control of gastric secretion?
Neurocrine
Endocrine
Paracrine
What is the neurocrine control of gastric secretion?
Acetylcholine from Parasympathetic- Vagus and ENS
What is endocrine control of gastric secretion?
Gastrin
What is paracrine control of gastric secretion?
Histamine
Local effect
What are the 2 mechanisms stimulating gastric secretions?
Cephalic phase
Gastric phase
Why is the cephalic phase of secretion important?
Create acidity before food arrives in the stomach so it can be sterilised immediately
What happens in the cephalic phase of secretion?
Sight, smell and taste of food causes an increase in vagus activity causing Ach release and gastrin release
What happens during the gastric phase of secretion?
Distension of stomach activates vagal and enteric reflexes, releasing Ach
Peptides in limen activate G cells to release gastrin
Gastrin and Ach act on ECL to release histamine
What happens in the cephalic phase on inhibition?
Stop eating causes a decrease in vagal activity
What happens in the gastric phase of inhibition?
Decrease of lumen pH causes a decrease in gastrin secretion so pH doesn’t drop too low
What kind of reaction is the gastric phase of inhibition?
Negative feedback
What initiates the intestinal phase of inhibition?
Acid or fat in duodenum
What does acid in the duodenum cause?
Enterogastric reflex and secretin release, decreasing gastrin secretion and stimulation
What does acid in the duodenum indicate?
Stomach is empty
What does fat in the duodenum cause?
GIP release, decreasing gastrin and parietal HCl secretion
What are enterogastrones?
Hormones released from gland cells in duodenal mucosa
What are the main enterogastrones?
Secretin
CCK
GIP
What are enterogastrones released in response to?
Acid Hypertonic solutions Fatty acids Monoglycerides in the duodenum
What do enterogastrones aim to do?
Prevent any acid getting into the duodenum
What are the 2 methods of action of enterogastrones?
Inhibit gastric secretion
Reduce gastric emptying- inhibit motility and contract pyloric sphincter
What is pepsinogen?
Inactive precursor to pepsin
What activated pepsinogen to turn into pepsin?
pH of below 3
Why is pepsin stored in its inactive form?
To prevent cellular damage
How is pepsin deactivated?
When the stomach reaches a neutral pH or pepsin enters and area of neutral pH
What are the mechanisms for control of pepsin?
Sight, smell and taste of food causes an increase in vagus activity causing Ach release and gastrin release- lowering pH and activating pepsin
Distension of stomach activates vagal and enteric reflexes, releasing Ach
Peptides in limen activate G cells to release gastrin
Gastrin and Ach act on ECL to release histamine- lowering pH and activating pepsin
Where is gastric mucus produced?
Epitelial cells and mucus neck cells
What is the role of gastric mucus?
Cytoprotective
Protects mucosal surface from mechanical injury
Protects against gastric acid corrosion and pepsin digestion
How does the mucus protect against gastric acid and pepsin?
Gastric acid neutralised by bicarbonate buffer
Pepsin deactivated by neutral pH
