AS 3, 4, 5

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Bobopudge
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56911
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AS 3, 4, 5
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2010-12-20 11:58:08
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  1. Describe the layers of the stomach wall
    • from inside to outside:
    • Mucosa
    • Submucosa
    • Musculosa
    • Serosa
  2. Describe the layers of the stomach mucosa
    • Surface epithelium
    • Lamina propria
    • Muscularis mucosa
  3. Decribe the layers of the Musculosa (Muscularis Externa)
    • Inner Oblique Muscles
    • Middle Circular layer
    • Outer Longitudinal Layer
  4. Describe the surface epithelium of the stomach wall
    • Its simple columnar epithelium:
    • - contains goblet cells -- secrete alkaline mucus
    • - contains gastric pits
    • --- lead into gastric glands
  5. Discuss the cells of oxyntic (parietal) glands in the stomach wall, including secretions
    • Neck cells - secrete mucus
    • Chief cells - secrete pepsiinogen (and some lipase, amylases)
    • Parietal cells - secrete acid and intrinsic factor
    • Mast-like cells (enterochromaffin-like cells) - secrete histamine
  6. Name 2 kinds of gastric glands, where are they located?
    • Oxyntic glands (proximal part of stomach)
    • Pyloric glands (antrum)
  7. State the location and contents of oxyntic glands
    • Located in proximal part of stomach and contains:
    • - mucous neck cells
    • - chief cells
    • - parietal cells
    • - mast-like cells
  8. Discuss the location and contents of pyloric glands
    • In antrum of stomach and contain:
    • - mucous cells - secrete mucus
    • - G cells - secrete gastrin into blood
  9. Discuss the 2 primary functions of the stomach
    Mechanical: storage of food, mixing of food, and emptying of chyme into duodenum

    Chemical: secretion (HCL, intrinsic factor, enzymes), absorption (alcohol, aspirin, water and electrolytes)
  10. Discuss receptive relaxation of the stomach
    • vago-vagal reflex
    • Stomach stretch causes fundus to relax
    • via VIP or NO
  11. Describe the mechanism of stomach mixing and emptying
    • pacemaker in middle of stomach
    • produce slow waves
    • travel to antrum of stomach
    • cause depolarization and contraction of smooth muscle (constriction rings)
    • pushes food towards pylorus
    • small amount enters duodenum
    • waves reach pyloric sphincter
    • tightening of pyloric sphincter
    • pushes most food upstream (retropulsion)
  12. Name 3 factors which increase slow waves in stomach and one which opposes it.
    • Increase slow waves:
    • - Acetylcholine from vagus
    • - Gastrin
    • - Stretch
    • Decrease slow waves:
    • - Noradrenaline from sympathetic nerves
  13. Name 3 factors which contract the pyloric sphincter. Name one which relaxes it
    • Contraction caused by:
    • - Sympathetic fibers
    • - Excitatory vagal fibers (Ach)
    • - Hormones
    • Relaxation caused by:
    • - Inhibitory vagal fibers (VIP or NO)
  14. What is an enterogastric reflex?
    • Reflexes that originate in the duodenum to inhibit gastric motility and secretions
    • Controlled by enteric nervous system
    • Due to distension in intestine
  15. What is the make up of gastric juice?
    • Mucus
    • Acid
    • Enzymes
    • - Pepsin
    • - Lipase
    • - Amylase
    • Histamine
    • Water, Bicarbonate, Ion, intrinsic factor
  16. What are the functions of gastric juice?
    • Water: liquifies food
    • Acid: acidifies, kills microbes, acidic environment for enzymes
    • Pepsins: digest proteins
    • Intrinsic factor: B12 absorption in ileum
    • Mucus: physical and chemical protection, lubricates food and protects stomach in acidic environment
  17. State the role of intrinsic factor and problems associated with its deficiency
    • Glycoprotein
    • Complexes with B12
    • Facilitates absorption in ileum

    • Deficiency:
    • occurs in stomach and intestinal disorders
    • results in vit B12 deficiency
    • - macrocytic anemia
    • - pernicious anemia
  18. Compare the pH level in the cytoplasm and gastric gland
    • Cytoplasm: pH 7
    • Gastric gland: pH 0.8
  19. Discuss HCl secretion in the stomach wall
    • In parietal cells
    • CO2 + Water = Carbonic acid
    • (enzyme involved; carbonic anhydrase)
    • Carbonic acid dissociates into H+ and bicarbonate
    • H+ actively pumped out of cell in exchange for potassium
    • (H/K ATPase)
    • Bicarbonate exchanged for Cl- across basolateral membrane
    • Cl- flows down its electrochemical gradient
  20. Discuss role of gastrin in HCL secretion
    • Secreted by G cells in stomach and duodenum
    • Travels of parietal cells in blood
    • Increases intracellular calcium
    • Release of acid
  21. State the major functions of gastrin hormone
    • It has 2 major functions: directly stimulates acid secretion from parietal cells & promotes histamine release from ECL cells
    • Other functions: increse gastric motility, relax ileo-cecal valve
  22. Name 3 factors which increase gastrin release from G cells
    • Amino acids in the stomach
    • Ach and GRP from vagus
    • stomach stretch via local reflexes
  23. Name 3 factors which inhibit gastrin release from G cells
    • acidity
    • somatostatin
    • secretin
  24. Discuss the roles and mechanism of histamine in acid secretion in the stomach
    • Strongest stimulant:
    • - released from ECL cells
    • - acts on H2 receptors in parietal cell
    • - increases cAMP inside cell
    • - increases acid secretion
    • Other functions: vasodilation
  25. Discuss the function and mechanism of Ach in acid secretion
    • Released from vagus
    • Function: increase all gastric secretions
    • Mechanism: Increases intracellular Calcium in parietal cell & Increases H/K ATPases in luminal membrane
  26. Discuss the role of Somatostatin in acid secretion
    • Paracrine agent
    • Released from D cells in gastric glands
    • Inhibits acid secretion in parietal cells (via decrease in cAMP)
    • Inhibits gastrin release from G cells
  27. Name 3 factors which inhibit acid secretion
    • Duodenal Distension (via enterogastric reflex)
    • Acids/fat/proteins in duodenum
    • - release of secretin and CCK
    • --- CCK acts on CCKA receptors on D cells; release somatostatin
    • Excess stomach acid

    *Note: duodenal distension may initially increase gastric; which actually increases acid secretion this occurs in the first part of the "intestinal Phase"
  28. Name 4 drugs which inhibit HCL secretion in the stomach
    • Muscurinic antagonists
    • H2 receptor antagonists i.e. cimetidine
    • PPI i.e. omeprazole
    • Prostaglandis i.e. misoprostol

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