Gastric Secretion Flashcards
Stomach structure
- Cardia - gastric juices manufactured
- Fundus - storage
- Antrum - connects stomach to duodenum
Histology of gastric glands
- Simple tubular structure
- Isthmus + neck : dividing cells + immature + maturing neck mucosal cells
Parietal cells
Isthmus region -> make HCl + intrinsic factor B12
Chief cells
Base of gastric gland -> peptin production
Mucous cells
Lining of stomach + gastric pits = mucus
Columnar cells
Thick coating for protection replaced 4-6 days
Composition of gastric juice
HCl, (155mM) , pepsinogen, intrinsic factor , KCl (15mM), NaCl small
Mechanism of acid secretion
- H+ generated by parietal cells
- OH- + CO2 -> HCO3- catalysed by carbonic anhydrase
- HCO3- Cl- , HCO3- outflow into blood = slight elevatioin in blood pH, alkaline tide (maintain IC pH in parietal cells)
- Cl- + K+ -> lumen of cannaliculus
- H+ K+ by potassium pump, K+ recycled
- H+ accumulation in canniculus generates osmotic gradient across membrane so outward diff. of water
Stomach produces X fluid / day
2L
Parasympathetic gastric stimulation
Vagal via ENS to HCL secretion -> pepsinogen -> mucus, gastrin -> vago-vagal reflex
Sympathetic gastric stimulation
Sympathetic fibres via ENS to blood vessels + gastric glands innervated
Gastrin
Endocrine stimulant of H+, mucus + pepsinogen secretion
-> released from G cells in central epithelium by ENS reflexes + lumina factors (peptides, aa)
Somatostatin
Paracrine inhibitor of gastrin from D cells
Histamine
Paracrine stimulant of H+ secretion from ECL of gastric mucosa binds to H2 receptors on parietal cells
Secretin
Endocrine inhibitor of H+ secretion
