Digestive System 2

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crzhazen
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76418
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Digestive System 2
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2011-03-31 10:36:28
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Digestive System
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Digestive System
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  1. Heartburn
    • Caused by abnormal relaxation of esophageal sphincter
    • Called gastroesophageal reflux disease (GERD) if it's chronic
    • Can cause dramatic inflammation and ulcers in esophagus
  2. Stomach
    • Muscular sac immediately inferior to diaphragm
    • Stores food: volume can increase from 50 ml to 4 L
    • Mechanically breaks up food, liquifies food
    • Begins chemical digestion of protein and fat
    • Produces chyme (soup of semi-digested food)
  3. Anatomy of Stomach
    • Lesser curvature along superior surface
    • Greater curvature along inferior surface
    • Stomach lined with rugae
    • Pyloric sphincter controls chyme entry into duodenum
  4. Gastric Banding
    • Bariatric Surgery
    • Small stomach pouch
  5. Sleeve Gastrectomy
    • Bariatric Surgery
    • 85% of the stomach is removed
  6. Gastric Bypass
    • Bariatric Surgery
    • Small stomach pouch that is attached to jejunum
  7. Anatomy of Stomach Wall
    • Mucosa has many cells filled with mucin that becomes mucus
    • Three layers of muscularis externa
  8. Gastric Pits
    • Depressions in gastric mucosa
    • Lined with epithelial cells
    • Opens up to glands in the bottom of each pit
  9. Mucous Cells
    Secrete mucus
  10. Parietal Cells
    Secrete HCl, intrinsic factor, and ghrenlin
  11. Chief Cells
    Secrete gastric lipase and pepsinogen (converted to pepsin)
  12. Enteroendocrine Cells
    Secrete hormones and paracrine agents that regulate digestion
  13. G Cells
    Secrete gastrin (stimulates secretion by parietal and chief cells and stimulate stomach contraction)
  14. Gastric Juice
    • Mixture of water, hydrochloric acid, digestive enzymes, mucous, hormones
    • Produced by gastric glands
    • Stomach produce 2-3 L/day
    • pH as low as .8
  15. Functions of HCl
    • Activates lingual lipase
    • Converts pepsinogen to pepsin
    • Breaks up connective tissue and plant cell walls
    • Converts Fe3+ to Fe2+ to be absorbed and used for hemoglobin synthesis
    • Destroys most ingested pathogens
  16. Pepsin
    • Pepsinogen secreted by chief cells
    • HCl removes some amino acids to form Pepsin
    • Pepsin digests proteins to shorter peptide chains
  17. Gastric Lipase
    • Produced by chief cells
    • With lingual lipase, plays a minor role in digesting fats
  18. Intrinsic Factor
    • Secreted by parietal cells
    • Essential for small intestine to absorb vitamin B12 (needed for hemoglobin synthesis)
  19. Hormones and Paracrine Agents
    • Secreted by enteroendocrine cells
    • Affect gut motility and appetite regulation
  20. Gastric Motility
    • Swallowing center of medulla stimulates stomach to relax and accommodate food
    • After food arrives, stomach contracts every 20 seconds to promote mechanical digestion and mixes food with gastric juice
    • Contractions generated by pacemaker cells in muscularis externa
    • With each contraction, 3 ml of chyme is secreted into duodenum
    • Allows neutralization of acid and slow digestion
    • Typical meal emptied from stomach in 4 hours
  21. Vomiting
    • Forceful ejection of chyme from the mouth
    • Pyloric and esophageal sphincters open due to increases in abdominal pressure and muscle contractions
    • Emetic center in medulla coordinates muscles
    • Induced by overstretching stomach or duodenum, chemical irritant (like alcohol), visceral trauma, intense pain or psychological stimuli
  22. Digestion and Absorption in the Stomach
    • Salivary and gastric enzymes partially digest protein, and digest small amounts of starch and fat
    • Most digestion occurs after chyme passes into small intestine
    • Stomach only absorbs a few things (aspirin and alcohol)
  23. Stomach's Protection from Acid
    • Mucous coat is very basic, so it protects against acid and enzymes
    • Epithelial cells have tight junctions to keep gastric juice out
    • Epithelial cells are replaced every 3-6 days
    • Old cells become part of chyme
  24. Peptic Ulcers
    • Erosion in the stomach walls
    • Most are caused by the bacteria Helicobacter pylori: Infection causes constant inflammation, and either reduces or increases amount of HCl secretion
    • Some caused by excess NSAID use
    • NSAID reduces ability to produce protective mucus
  25. Parasympathetic Nervous System Regulation of Gastric Function
    Increases gastric motility while eating and in anticipation of food (through myenteric plexus)
  26. Sympathetic Nervous System Regulation of Gastric Function
    Suppresses gastric motility when the stomach empties
  27. Cephalic Phase
    Stomach controlled by brain
  28. Gastric Phase
    Stomach controls itself
  29. Intestinal Phase
    Stomach controlled by small intestine
  30. Cephalic Phase
    • Stomach responds to sight, smell, taste or thought of food
    • Hypothalamus relays signal to medulla
    • Parasympathetic neurons from medulla stimulate enteric nervous system to activate gastric secretion
  31. Gastric Phase
    • Ingested food stimulates gastric secretion by activating short (myenteric) and long (vasovagus) reflexes
    • Muscularis externa muscles conntract
    • Acetylcholine and histamine and gastrin stimulates gastric secretion
  32. Intestinal Phase
    Duodenum inhibits gastric secretion by inhibiting parasympathetic neurons in the medulla and stimulating sympathetic neurons
  33. The Liver
    • Gland just inferior to the diaphragm
    • Secretes bile to aid in digestion of lipids
    • Plays many non-degestive roles: detoxification, nutrient and vitamin storage, RBC breakdown, and coagulant secretion
  34. Anatomy of the Liver
    • Four lobes: right, left, quadrate, caudate
    • Falciform ligament separates left and right
    • Porta Hepatis: opening between quadrate and caudate lobes
    • Hepatic portal vein, proper hepatic artery, and bile passages enter liver here
  35. Blood Supply to Liver
    • About 1/3 from proper hepatic artery
    • About 2/3 from hepatic portal vein
    • From capillaries in esophagus, stomach, and intestines
  36. Hepatic Lobules
    • Central canal and sinusoids filled with blood
    • Epithelial cells lining hepatocytes have many gaps (fenestrations) between them to allow blood plasma entry
  37. Hepatocytes
    • Absorb glucose, amino acids, iron, vitamins, and other nutrients after a meal
    • Remove and degrade hormones, toxins, bile pigments and drugs
    • Secrete albumin, lipoproteins, clotting factors, angiotensinogen
    • Between meals (when glucagon present), they break down glycogen and release glucose
    • Form and secrete bile
  38. Hepatic Triad
    • Each lobule has 6 triads, which consists of two blood vessels (branches of proper hepatic artery and hepatic portal vein) and bile duct
    • Proper hepatic artery and hepatic portal vein supply blood to sinusoids
    • After filtering through sinusoids it's collected in the central canal
    • Then flows to right and left hepatic vein and drains into inferior vena cava
  39. Bile Secretion
    • Bile is secreted into bile canaliculi to get to ductule in triad
    • Bile flows into common hepatic duct on inferior side of liver
    • Then flows into the bile ducts
  40. Movement of Bile
    • Bile duct joins with pancreatic duct in hepatopancreatic ampulla
    • Hepatopancreatic sphincter regulates passage of bile and pancreatic juice into duodenum
  41. The Gallbladder
    • Small sac on inferior side of liver
    • Stores and concentrates bile
    • Absorbs water and electrolytes
    • Neck leads into cystic duct
  42. Bile
    • Yellow-green fluid containing water, minerals, bilirubin, cholesterol, bile salts (lipids)
    • Bacteria in large intestine metabolize biliruben to urorubin
    • Responsible for brown color in feces
  43. Bile Salts
    • Break up large lipid droplets (emulsification)
    • This increases surface area so that more enzymes can contact lipids and metabolize them
  44. Bile Storage
    • Liver fills bile duct with bile
    • Stuck in duct until hepatopancreatic sphincter opens
    • Sphincter only opens when fat in SI triggers cholecystokinin production
  45. Bile Concentration
    • Bile overflows into gallbladder until duct empties
    • As it is stored, water is absorbed and bile becomes more concentrated
    • Most bile reabsorbed by SI and returned to liver through hepatic portal vein

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