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secretion of the GI system (gastric secretion (HCL (H+ and Cl- are…
secretion of the GI system
gastric secretion
HCL
H+ and Cl- are secreted separately by parietal cells into stomach lumen
H+ ions are generated as carbonic anhydrase converts
CO2 + H2O <=> H2CO3 <=> H+ + HCO3-
H+ is actively transported across the plasma membrane via a H+/K+ pump
(proton pump)
as HCO3- is ejected from the cell a Cl- is brought in to balance the charge, these chloride ions are able to diffuse through the apical surface membrane via chloride channels
alkaline tide:
surge of HCO3- into interstitial fluid after you ingest a meal which makes blood slightly alkaline
gastrin
produced by G cells of the stomach
stimulates chief cells to make pepsinogen
stimulates the stomach's SMCs to contract
stimulates parietal cells to secrete acid via ECL cells which secrete histamine
intrinstic factor
secreted by parietal cells
it facilitates the absorption of vitamin B12 in the ileum
pepsinogen
chief cells produce pepsinogen, which in the presence of HCL becomes activated pepsin
pepsin = an enzyme that breaks down proteins
duodenal secretion
cholecystokinin (CCK)
its release is triggered by arrival of
lipids
in the duodenum
it stimulates SMC contraction in gallbladder, stimulates opening of sphincter of Oddi, inhibits gastric contractions
secretin
its release is triggered by increase in H+ (low pH) and fatty acid arrival in duodenum
it promotes the release of pancreatic enzymes
exocrine of pancreas
gastrin inhibitory peptide
stimulates the pancreas to secrete insulin
its release is triggered by presence of glucose, amino acids, and/or fatty acids in the small intestines
endocrine of pancreas
exocrine pancreatic secretion
digestive enzymes (acinar cells)
secreted as inactive digestive proenzymes (
zymogen
) in an alkaline solution and are activated by enteropeptidases in the brush border when they reach the small intestines
pancreatic alpha-amylase: break down starches
pancreatic lipase (
hydrophilic)
: break down certain complex lipids
nucleases: break down DNA and RNA
proteolytic enzymes: break down proteins
aqueous component of pancreatic secretion (centroacinar cells and intercalated ducts)
centroacinar cells make HCO3-
bile secretion