Composition and functionof gastric secretions 2. Pepsinogen(precursor of pepsin) digestion of proteins 3. Mucus forms a protective barrier: Mucus-bicarbonate barrier 4. Intrinsic factor combines with vitamin b to make it absorbable 16
16 Composition and function of gastric secretions 2. Pepsinogen (precursor of pepsin) ➢ digestion of proteins 3. Mucus ➢ forms a protective barrier: Mucus-bicarbonate barrier 4. Intrinsic factor ➢ combines with vitamin B12 to make it absorbable
Acid secretion HCI secretion The parietal cell -resting Mitochondria bulovesicles光面管泡 Canaliculus 微管 6 LUMEN OF GLAND
17 HCl secretion 光面管泡 微管
HCl secretion Parietal cell -secreting Tubulovesicles fuse with canaliculus. increased surface area and numbers of h+K+ATPase increases acid secretion into lumen f gut. Acid secretion is against a 3 million fold concentration gradient [H+]inside 4 x108M H*outside =0.1M NEEDS ENERGY
18 HCl secretion
HCI secretion Gastric acid H cl parietal ce lls at Proton pump Mitochondia园 Canaliculus HCo. +OH Alkaline tice HCOs sm日
19 HCl secretion
HO Stomach PH<2 Lumen C H Carbonic Anhydrase H CO3 CO, +H. HCO3 cO2 Blood PH3.4
20 Blood Stomach Lumen CO2 CO2 + H2O Carbonic Anhydrase H2CO3 H HCO3 K ~ Cl Cl pH<2 pH>7.4 H2O