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Describe the layers of the stomach wall
- from inside to outside:
- Mucosa
- Submucosa
- Musculosa
- Serosa
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Describe the layers of the stomach mucosa
- Surface epithelium
- Lamina propria
- Muscularis mucosa
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Decribe the layers of the Musculosa (Muscularis Externa)
- Inner Oblique Muscles
- Middle Circular layer
- Outer Longitudinal Layer
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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
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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
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Name 2 kinds of gastric glands, where are they located?
- Oxyntic glands (proximal part of stomach)
- Pyloric glands (antrum)
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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
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Discuss the location and contents of pyloric glands
- In antrum of stomach and contain:- mucous cells - secrete mucus
- - G cells - secrete gastrin into blood
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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)
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Discuss receptive relaxation of the stomach
- vago-vagal reflex
- Stomach stretch causes fundus to relax
- via VIP or NO
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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)
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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
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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)
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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
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What is the make up of gastric juice?
- Mucus
- Acid
- Enzymes
- - Pepsin
- - Lipase
- - Amylase
- Histamine
- Water, Bicarbonate, Ion, intrinsic factor
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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
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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
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Compare the pH level in the cytoplasm and gastric gland
- Cytoplasm: pH 7
- Gastric gland: pH 0.8
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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
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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
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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
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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
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Name 3 factors which inhibit gastrin release from G cells
- acidity
- somatostatin
- secretin
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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
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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
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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
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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"
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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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