Neural & Hormonal Regulation of the Mouth, Esophagus, and Stomach

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nataliekrier
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192888
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Neural & Hormonal Regulation of the Mouth, Esophagus, and Stomach
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2013-01-16 22:52:59
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Neural Hormonal Regulation Mouth Esophagus Stomach
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Neural & Hormonal Regulation of the Mouth, Esophagus, and Stomach
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  1. 3 types of GI glands

    2 types of GI secretions
    • tubular glands
    • peripheral compound glands
    • mucous glands

    • digestive enzymes
    • mucous
  2. Nervous control of motility and secretion
    • enteric nervous system
    • parasympathetic innervation
    • sympathetic innervation
    • afferent sensory innervation
  3. Enteric nervous system
    • esophagus to anus
    • - acetylcholine (excitatory)
    • - norepinephrine (inhibitory)
    • - serotonin, dopamine, cholecystokinin, substance P, vasoactive intestinal peptide (VIP), somatostatin, leu-enkephalin, metenkephalin, bombesin
    • 2 components
    • - submucosal (Meissner's) plexus (regulates mucosa)
    • - myenteric (Auerbach's) plexus (regulates motor activity along the gut)
  4. Parasympathetic innervation
    • excitatory
    • preganglionic neurons
    • - vagus
    • - sacral spinal cord
    • postganglionic neurons
    • - within submucosal or myenteric plexus
  5. Sympathetic innervation
    • usually inhibitory
    • preganglionic neurons
    • - spinal cord (T5-L2) and enter sympathetic chains to travel to specific outlying ganglia
    • postganglionic neurons
    • - within cervical/mesenteric ganglia
  6. Afferent sensory innervation
    • arise from cell bodies within enteric nervous system
    • short reflex
    • - directly stimulate or inhibit neighboring enteric neurons
    • long reflex
    • - alternatively synapse on neurons in prevertebral sympathetic ganglia that then project back to the enteric nervous system
    • long reflex
    • - other afferent fibers originate from cell bodies in dorsal root ganglia or cranial nerve nuclei and send input to neurons in spinal cord and brainstem that then project back to the enteric nervous system
  7. Hormonal control of motility and secretion
    • enteroendocrine cells
    • - open cells
    • - closed cells
    • minimal reg of motility
    • major reg of secretion
  8. Specific digestive enzyme secreted in the mouth
    salivary amylase
  9. Salivary amylase
    • initial digestion of carbs
    • resp for hydrolyses of 30-40% of ingested starch to maltose
  10. Salivary components
    • IgA
    • lysozyme
    • salivary-amylase (ptyalin)
    • mucous (glycoproteins)
    • lactoferrin
    • lungual lipase
  11. Salivary gland secretion
    • begins in the acini
    • inorganic ion conc altered along duct
    • Na+ (active) and Cl- (passive) absorbed in ducts
    • K+ (active) and HCO3- secreted
    • flow rate affects ion conc
  12. Conditioned and unconditioned secretions in the mouth
    • con - Pavlovial reflex
    • uncon - parasym/sym work together
  13. Parasympathetics - mouth
    • increases secretion and is the primary control (watery saliva, less protein)
    • - sensory neurons in mouth, tongue, and pharynx
    • - solitary tract
    • - preganglionic sup/inf salivatory nuclei
    • - postganglionic submandibular/otic ganglia
    • - glands
  14. Sympathetics - mouth
    • modest increase in secretion (thicker saliva, more protein)
    • - preganglionic neurons in thoracic spinal cord
    • - postganglionic neurons in sup cervical ganglia
    • - glands
    • (excessive stimulation can be inhibatory via vasoconstriction)6y
  15. Hormonal control of motility and secretion in the mouth
    negligible
  16. Digestion and absorption in the mouth
    • digestion of carbs by salivary amylase
    • negligible absorption
    • - absorption of low mlcl weight drugs unstable in the stomach/vulnerable to first-pass metabolism
  17. Organization of the esophagus
    • nonkeritanized stratified squamous epithelium
    • esophageal cardiac glands (lamina propria)
    • - alkaline mucous
    • esophageal glands (submucosa)
    • mixed skeletal/smooth m in externa
  18. Phases of swallowing
    • reg by medullary swallowing center
    • voluntary phase
    • - bolus moved to back of mouth
    • pharyngeal phase
    • - 1-2 sec
    • - bolus pushed thru UES
    • esophageal phase
    • - 8-10 sec
    • - peristalsis to stomach
  19. Hormonal control of motility and secretion in the esophagus
    negligible
  20. Digestion and absorption in the esophagus
    negligible
  21. Organization of the stomach
    • - simple columnar epithelium
    • - gastric pits
    • - gastric glands (lamina propria)
    • - rugae (mucosa/submucosa)
    • cardiac region
    • fundus/body region
    • pyloric region
  22. Cells of the cardiac region of the stomach
    mostly mucous cells
  23. Cells of the fundus/body of the stomach
    • stem cells
    • mucous cells (surface vs. neck)
    • parietal (oxyntic) cells
    • - gastroferrin
    • - gastric intrinsic factor
    • - hydrochloric acid
    • chief (zymogenic) cells
    • - pepsinogen
    • - gastric lipase
    • enterochromaffin like cell
    • - histamine
    • enteroendocrine cells
    • - serotonin (increases motility)
  24. Cells of the pylorus of the stomach
    • (not a lot of acid production; many mucous cells)
    • few parietal/chief cells
    • many mucous cells
    • G cells
    • - gastrin (increases acid secretion)
    • D cells
    • - somatostatin (inhibits enteroendocrine cell secretion)
  25. Actively secreted hydrochloric acid
    • via H+ K+ exchanger and chloride channel
    • anti-microbial
    • promotes ferrous (Fe2+) rather than ferric (Fe3+)
    • provides pH for pepsin
  26. Nervous control of motility in the stomach
    • local
    • - mesenteric plexus reflexes activated by stretching; increases pyloric pump activity and inhibits pyloric sphincter contraction
    • negative feedback from duodenum
    • stimulated by
    • - distension/irritation of duodenum
    • - increased acidity of duodenal chyme 
    • - hypertonic or hypotonic chyme
    • - presence of breakdown products, esp protein and fats
    • 3 mechanisms
    • - directly via enteric nervous system (short)
    • - sensory fibers that synapse on prevertebral sympathetic ganglia neurons that supply inhibitory input to enteric nervous system in stomach (long)
    • - vagovasal reflexes where sensory fibers in vagus send input to brainstem to inhibit excitatory parasympathetic innervation from vagus to enteric nervous system of stomach (long)
    •  
  27. Hormonal control of motility in the stomach
    • local
    • - distension of stomach stimulates gastrin release from enteroendocrine cells in pyloric glands
    • - gastrin has mild ability to increase pyloric pump activity
    • intestinal feedback
    • - cholecystokinin
    • - secretin
    • - gastric inhibitory peptide
  28. Cholecystokinin
    • - released by I cells in duodenum in resp to fatty chyme
    • - competitively inhibits gastrin-dependent increase in motility
  29. Secretin
    • - released by S cells in duodenum in resp to acidic chyme
    • - weak affect on decreasing stomach motility
    • - decreases all gastric secretions from gastric glands
  30. Gastric inhibitory peptide
    • - released by K cells in the duodenum in resp to high fat chyme
    • - weak activity for decreasing stomach motility
  31. Major digestion-related secretory products released
    • mucous
    • pepsinogen
    • hydrochloric acid
  32. Mucous
    • - secreted basally but increased by direct contact of goblet cells with chemicals and foodstuffs
    • - gastrin acts directly upon goblet cells to increase mucous secretion
  33. Pepsinogen
    • - chief cell
    • neuronal control
    • - acetylcholine: from vagal postganglionic neurons/enteric neurons; stimulates increased release
    • - acidic lumen pH: activates enteric neurons to stimulate increased release
    • - negative feedback reflex loops: from sm int; decrease stomach motility also act to decrease secretion
    • hormonal control
    • - secretin: decreases all gastric secretions from gastric glands
  34. Hydrochloric acid
    • - parietal cell
    • neural control
    • - acetylcholine: from vagal postganglionic/enteric neurons; stimulates increased release
    • - vagal postganglionic/enteric neuron stimulation of enterochromaffin cells; stimulates histamine release to bind H2 receptors on parietal cells to stimulate acid release
    • - negative feedback reflex loops: from sm int; decrease acid secretion; same loops that act to decrease stomach motility
    • hormonal control
    • - gastrin-17
    • - secretin
  35. Pepsin 1
    • - 10-20% of protein digestion
    • - protease from inactive pepsinogen precursor (chief cells)
    • - max activity at pH 2-3
  36. Lingual lipase
    • - less than 10% of triglyceride digestion
    • - in saliva
  37. Salivary amylase
    • - 20-40% of starch digestion
    • - in saliva
    • - upon mixing of food with gastric secretions (1 hr after ingestion), pH falls below 4 inactivating salivary amylase

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