GI 4 Flashcards
what is the acid secretion of the gastric mucosa?
parietal cells
-1-3L of gastric acid (HCl) produced daily with a pH as low 1
-stimulated by gastrin from G-cells, histamine from enterochromaffin-like cells (ECL) or ACh from ENS neurons via long and short reflexes
what are the gastric acid functions?
-stimulates release of pepsinogen from chief cells, cleaves pepsinogen to pepsin (digests proteins)
-denatures proteins making it easier for pepsin to function
-kills bacteria and other ingested microorganisms
-inactivates amylase from saliva
-stimulates D cells to release somatostatin
what is acid secretion in the stomach?
-free H+ actively transported across apical membrane
-water dissociates to H+ and OH- freeing up more H+ to be actively transported
-OH- combines with CO2 via A to generate HCO3-
-HCO3- exchanged for Cl- at basolateral membrane
-Cl- diffuses across apical membrane through open channels following electrochemical gradient
what is the graph of acid secretion in the stomach?
what does the stimuli for acid secretion cause?
apical H+/K+ ATPase, Cl- and K+ transporters stored in vesicles
-stimuli cause exocytosis and insertion of apical transporters
-excessive acid treated with H2 receptor antagonists or proton pump inhibitors
what is the spiderweb of gastric acid secretion?
what are the enteric hormones that inhibit gastric H+ secretion?
-intestinal hormones can also inhibit acid secretion
what is the graph of gastric digestive enzyme secretion?
what is paracrine secretion?
ECL
-histamine
-activates H2 receptors on parietal cells to stimulate HCl secretion
Parietal cells
-intrinsic factors
-forms a complex with Vit B12 (can’t be reabsorbed on its own) so it can be absorbed (imp in metabolism, RBC production)
D cell
-somatostasin
-negative feedback for acid secretion (G cells, parietal cells and ECL cells)
-inhibit pepsinogen release
what is the graph of stomach graph?
what is mucus secretion in the gastric mucosa?
mucus and HCO3- secreted from mucous cells
-mucus secretion stimulated by parasympathetic input and irritation
-HCO3- by parasympathetic input and H+
-creates physical and chemical barrier
what is a peptic ulcer?
-a sore or break in the lining of the stomach or duodenum
-excessive acid production: gastric secreting tumors
-nonsteroidal anti-inflammatory drugs (NSAIDS) (ibuprofen and aspirin)
-helicobacter pylori (major cause)
what is the history of H. pylori?
-for decades stress, spicy foods and over production of acid was believed to cause peptic ulcers
-Barry Marshall and Robin Warren hypothesized bacteria caused the majority of peptic ulcers (1982)
-nobel prize in physiology and medicine in 2005
what is H. pylori?
-breaks down urea and makes it into ammonia buffer
-wants normal pH so imbeds in it
-large levels of ammonia become toxic to the epithelial cells and mucous secreting cells
-break down layer so acid can break down wall
what is the intestinal phase?
-5.5L of food, fluid and secretions (2 ingested+ 1.5 saliva+ 2 gastric) enter the small intestine, an additional 3.5L added from hepatic (0.5), pancreatic (1.5) and intestinal (1.5)
-motility regulated to ensure proper digestion and absorption (allow enough time to get reabsorbed)
-combination of segmental and peristaltic contractions mix the chyme with enzymes and expose digested nutrients to mucosal epithelium for absorption (7.5L absorbed mainly in duodenum and jejunum)
-parasympathetic innervation, gastric and cholecystokinin promote motility
-sympathetic innervation inhibits
what is used in the intestinal phase?
-villi increase surface area available for absorption and secrete mucus (goblet cells)
-crypts contain hormone and fluid secretory cells + stem cells
-most nutrients are absorbed into capillaries and in the villi
-fats enter lacteals (blunt-ended lymph vessels) of lymphatics
what does the liver act as?
a biological filter (in hepatic portal system)
-contain a variety of enzymes that metabolizes drugs and xenobiotics (foreign) and clear them from the blood stream before it can proceed to systematic circulation
-drugs given orally commonly have a higher dose than IV
what is the summary of the intestinal secretions that promote digestion?
3.5L of secretions enter the lumen of the small intestine
-digestive enzymes (intestine epithelium: brush border enzymes and pancreas)
-bile (liver, stored in gallbladder)
-bicarbonate (pancreas)
-mucus (goblet cells)
-isotonic saline (crypt cells): lubricates contents of gut
