Gastric Secretion Flashcards
What is the function of the fundus of the stomach?
Storage
What are the functions of the body of the stomach?
- Storage
- Addition of mucus
- Addition of HCL
- Activation of pepsinogen
- Addition of intrinsic factor
What is the function of the antrum of the stomach?
- Mixing/grinding
- Gastrin
What do the mucous neck cells secrete?
Mucus
What do the chief cells secrete?
Pepsinogens
What do the parietal cells secrete?
- HCL
- Intrinsic factor
What is the pH of the lumen of the stomach?
<2
What is the pH of the blood?
7.4
What does carbonic anhydrase catalyse?
Reaction of CO2 to carbonic acid
Describe the movement of ions between the blood, and stomach lumen.
- CO2 from the blood combines with H20 to form carbonic acid.
- Hydrogen from the carbonic acid is pumped out of the cell as potassium is pumped into the cell.
- Bicarbonate remains which is pumped into the blood as Cl is pumped into the cell.
- The Cl then moves into the lumen of the stomach
- Water passes from blood to stomach lumen paracellularly
Slide 5
Slide 5
What are the 3 mechanisms which control gastric acid secretion?
- Neuroncrine
- Endocrine
- Paracrine
How is neurocrine control of gastric acid secretion achieved?
Via vagus and local reflexes
How is endocrine control of gastric acid secretion achieved?
Via gastrin
How is paracrine control of gastric acid secretion achieved?
Via histamine
Describe the cephalic phase of gastric acid secretion.
- Sight, smell and taste of food increases action of Vagus nerve.
- Produces an increase in ACh which acts on parietal cells.
- Vagus activate G cells which increase gastrin release which acts on parietal cells
- Gastrin and ACh act on ECL cells which increase release of histamine which act on parietal cells
Describe the 3 parts of the gastric phase of gastric acid secretion.
- Arrival of food produces distension of stomach. Produces vagal and enteric reflexes releasing ACh acting on parietal cells
- Peptides in lumen activate G cells which release gastrin acting on parietal cells
- Gastrin/ACh act on ECL cells which release histamine acting on parietal cells
How is gastric acid secretion inhibited at the cephalic stage?
Stopping eating decreases vagal activity
How is gastric acid secretion inhibited at the gastric phase?
Decrease in pH as a result of an increase in HCl leads to a decrease in gastrin
How does acid in the duodenum inhibit gastric acid secretion at the intestinal phase?
-Produces enterogastric reflex and secretin release which both lower gastrin secretion and gastrin stimulation of parietal cells
How does fat in the duodenum inhibit gastric acid secretion at the intestinal phase?
Leads to GIP release which decreases gastrin secretion and parietal HCl secretion
What are enterogastrones?
Hormones released from gland cells in duodenal mucosa
Give 3 examples of enterogastrones.
- Secretin
- Cholecystokinin
- GIP
When are enterogastrones released?
In response to acid, hypertonic solutions, fatty acids or monoglycerides in duodenum
What do enterogastrones do?
Act collectively to prevent further acid build up in duodenum
What are the 2 strategies used by enterogastrones?
- Inhibit gastric acid secretion
- Reduce gastric emptying (inhibit motility/contract pyloric sphincter)
What secretes pepsinogen?
Chief cells
When is pepsinogen converted to pepsin?
Low pH <3
Zymogen
Inactive precursor
What does zymogen storage prevent?
Cellular digestion
When are pepsins inactivated?
At neutral pH
What are mechanisms for pepsin control of pepsin secretion parallel to?
Mechanisms for HCl secretion
Where is gastric mucus produced
Produced by surface epithelial cells and mucus neck cells
Describe the cytoprotective role of gastric mucus.
-Protects mucosal surface from mechanical injury
Neutral pH protects against gastric acid corrosion and pepsin digestion
What is the only essential function of the stomach?
Secretion of intrinsic factor
What produces intrinsic factor?
Parietal cells
What is intrinsic factor required for?
Vitamin B12 absorption
Where is the intrinsic factor/B12 complex absorbed?
Ileum
What can failure of intrinsic factor lead to?
Pernicious anaemia which is failure of erythrocyte maturation
