Lecture 28 - Gastric Acid Secretion Flashcards
What are the components of gastric secretions?
Acid
Pepsin
Intrinsic factor
Mucus
What is the function of acid in gastric secretions?
Protective role
Denature proteins
Optimum pH for many digestive enzymes
Render fluid isosmotic
- (150 mM HCl - (HCO3-) - neutralised part)
What is the function of pepsin?
Protein digestion
What is the role of intrinsic factor in gastric secretions?
Vitamin B12 absorption (DNA, red blood cells, pernicious anaemia)
What is the role of mucus in gastric secretions?
Protects against acid and mechanical forces
What luminal secretion occurs at the LES and cardia?
Mucus
HCO3-
What luminal secretion occurs at the fundus and body?
H+
Intrinsic factor
Mucus
HCO3-
Pepsinogens
Lipase
What luminal secretion occurs at the antrum and pylorus?
Mucus
HCO3-
What is the apical HCO3-/Cl- exchanger in salivary duct cells driven by?
Cl- via CFTR
Where does the HCO3- come from in salivary duct cells?
Either carboanhydrase reaction or from basolateral side
What cells make up the gastric glands in body of stomach?
Surface cells
Mucus secreting cells
Oxyntic (parietal) cells
Chief cells
Enterochromaffin like (ECL) cells
What do the surface cells in gastric glands secrete?
HCO3-
What do the parietal cells in gastric glands secrete?
Acid
Intrinsic factor
What do the chief cells in gastric glands secrete?
Pepsinogen
What do ECL cells in gastric glands secrete?
Histamine
How much is secreted by the gastric glands per day?
2-3 L per day
When do gastric secretion composition change?
Eating or fasting phase
What do ECL cells sit in close proximity to?
Oxyntic (parietal) cells
What is the rate of gastric secretion between meals?
15-30ml/h
What is gastric secretion between meals secreted by?
Surface cells
What is the gastric secretion composition between meals?
Isosmotic solution with similar [Na+] as plasma but higher [HCO3-]
Also mucus
What is the rate of gastric secretion while eating?
150ml/hr (5-10x higher)
What is the composition of gastric secretion while eating?
Isosmotic (150 mM) solution of HCl produced by parietal cells
Pepsinogen
Intrinsic factor
More mucus
What is the final gastric secretion osmolality and why?
Remember surface cells secrete HCO3-
H+ + HCO3 <=> H2CO3 <=> H2O + CO2
Therefore final gastric secretion has an osmolality of ≈ 200 mOsmol/L