Digestive System Part 2

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Digestive System Part 2
2011-04-10 09:54:12
Stomach GI Tract

Part 2
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  1. Processes of Digestion:
    • 1. Food ingested: by mouth
    • 2. Mechanical digestion: chewing
    • 3. Chemical digestion: Salivary amylase begins chemical breakdown of starch
    • 4. Propulsion: initiated by swallowing
    • 5. Pharynx and Esophagus: pass food from mouth to stomach
  2. Pharynx
    • passes food and fluids to esophagus and gives air to trachea
    • -lined with stratified squamous epithelium and mucus glands
    • -two skeletal muscle layers for swallowing
    • 1. inner longitudinal
    • 2. outer pharyngeal constricters
  3. Deglutition
    Swallowing: involving 22 seperate muscle groups and involves 3 phases
  4. Buccal Phase:
    • (within deglutition)
    • bolus is forced into oropharynx
  5. Pharyngeal-esophageal phase:
    • (within deglutition)
    • -controlled by medulla and lower pons
    • routes sealed off except into digestive tract (probably so we don't choke)
  6. Peristalsis:
    • (within deglutition)
    • moves food through pharynx and esophagus
  7. Esophagus
    • muscular tube going from laryngopharynx to stomach
    • travels through mediastinum and pierces diaphragm
    • joins stomach at cardiac orifice
  8. Esophageal mucosa
    nonkeratinized stratified squamous epithelium
  9. What happens when the esophagus is empty?
    its folder longitudinally and flattened
  10. The muscle changes from what to what in the esophagus?
    skeletal (superiorly) to smooth muscle (inferiorly)
  11. When does a Hiatal Hernia occur?
    • when the cardiac (gastroesophageal) Sphyncter does not close when food is in stomach
    • -causes pregnancy, obesity, weak sphyncter
    • -superior stomach can move into thoracic cavity
  12. Gastro Esophageal Reflux Disease (GERD)
    • is a result with acid irritating the esophagus
    • -if chronic then esophageal cancer can result
  13. What does the salivary gland secrete?
    • Amylase: carbs-glucose
    • Lingual Lipase: fats-fatty acids
  14. What does the Stomach secrete?
    • Pepsin: proteins-polypeptides
    • HCl: pepsinogen-pepsin, destroys pathogens
  15. What does the Liver secrete?
    Bile Salts: fats-fatty acids
  16. What does the Pancreas secrete?
    • Amylase: carbs-glucose
    • Trypsin: polypeptides-peptides
    • Lipase: fats-fatty acids
  17. What do the small intestines secrete?
    • peptidase: peptides-amino acids
    • sucrase: sucrose-glucose
    • maltase: maltose-glucose
    • lactase: lactose-glucose
  18. What happens when bolus goes into stomach?
    chemical breakdown of proteins and food is converted into chyme
  19. Cardiac Region
    surrounds cardiac orifice and cardic sphincter
  20. Fundus
    dome shaped region beneath diaphragm
  21. Pyloric Region:
    • made of antrum and canal whih terminates at pylorus
    • -pylorus extends to duodenum
  22. What does the greater omentum help with?
    holding the small intestines in place
  23. What is the Nerve Supply like in the Stomach?
    sympathetic and parasympathetic fibers of autonomic nervous system
  24. Blood Supply in the stomach comes from where?
    • celiac trunk (gastric artery
    • corresponding veins (gastric veins)

    part of hepatic portal system
  25. What does the Muscularis layer do in the Stomach?
    • allows stomach to churn, mix, and pummel food physically
    • breaks down food into smaller fragments
  26. What is the Epithelial lining in the Stomach composed of?
    Goblet cells: produce double layer coat of alkaline insoluble mucus with bicarbonate in between
  27. Gastric Pits:
    contain gastric glands that secrete gastric juice, mucus, and gastrin
  28. Mucous Neck Cells (Gastric Pit)
    secrete acid mucus
  29. Parietal Cells (Gastric Pit)
    secrete HCl and intrinsic factor needed for Vitamin B12 (nucleic acid metabolism and RBC maturation) absorption in small intestines
  30. Chief Cells (Gastric Pit)
    produce pepsinogen

    (pepsinogen activated to pepsin by HCl in stomach and pepsin breaks down proteins to polypeptides)
  31. Enteroendocrine cells (Gastric Pit):
    • Secretes:
    • -Gastrin: stimulates gastric glands to increase there secretion, stimulates gastric emptying
    • -Histamine: activates parietal cells to release HCl
    • -Serotonin: stimulates gastric muscle contractions
    • -Cholecystokinin (CCK): allows pancreatic and bile enzymes to be released
    • -Ghrelin: release when stomach is empty stimulating hunger and appetite
  32. To Keep the stomach from digesting itself, its mucosal barrier has what?
    • thick coat of bicarbonate-rich mucus on wall
    • epithelial cells joined by tight junctions (damaged cells are replaced quickly)
    • gastric glands that have cells impermeable to HCl
  33. What are Stomach ulcers caused by?
    • bacteria Helicobacter pylori (H. pylori)
    • burrs a hole through the mucusa and allows HCl to further irritate the lining
  34. How does Helicobacter Pylori work to create a stomach ulcer?
    • 1. bacteria secretes ammonia, neutralized the HCl
    • 2. secretes cytotoxin that damages mucosal cells
    • 3. produces proteins that sepertate cells tight junctions
  35. What are the 5 things the stomach does?
    • 1. holds food
    • 2. degrades food physcially and chemically
    • 3. delivers chyme to small intestine
    • 4. Enzymatically digests proteins to polypeptides to pepsin
    • 5. secretes intrinsic factor required for absorption of vitamin B12 (needed for DNA synthesis and erythropoeisis)
  36. How many phases are there in Gastric Secretion and what are they?
    Cephalic (reflex), Gastric, and Intestinal phase
  37. Cephalic (reflex) phase: Gastric Secretion
    • happens before food enters stomach
    • -Excitatory: think, smell, taste, see
    • enhanced secretory activity (reflex) only happens when we want or like food we see
    • -Inhibitory: loss of appetite/depression, decrease in stimulation of parasympathetic division

    Enteric ganglionic neurons stimulate the stomach glands
  38. Gastric phase: (Gastric secretion)
    • food enters stomach
    • last 3-4 hours
    • Excitatory: stomach distension,
    • activation of stretch receptors,
    • activation of chemoreceptors by peptides caffeine, and lowering pH,
    • release of gastrin in blood (stimulates gastric glands to increase secretion=gastric emptying
    • Inhibitory: pH lower than 2
    • emotional upselt overrides parasympathetic division
    • *ACh release, stimulates more gastric juice
    • rise in pH stimulates gastrin secretion and HCl release (more acid for protein digestion)
  39. Intestinal Phase: (Gastric Secretion)
    Excitatory: low pH; partially digested food enters duodenum and encourages gastric gland activity

    • Inhibitory: distension of duodenum, presence of fatty, acidic, hypertonic chyme, and/or irritants in duodenum
    • -initiates inhibition of local reflexes
    • -closes pyloric sphincter
    • -small intestines release enterogastrones (CCK and Secretin), inhibit gastric secretion
  40. HCl secretion is stimulated by...
    • ACh
    • histamine
    • gastrin
  41. Antihistamines block___ receptors and decrease ____ release.
    • H2
    • HCl
  42. Stomach pressure remains constant until ___ of food is ingested.
    1.5 L
  43. How much food can the stomach hold?
  44. How long is the stomach when it is empty and how big can it get?
    • 6-10 inches
    • to the top of the pelvis when filled
  45. Peristaltic waves move toward the pylorus at rate of __ per________.
    • 3
    • minute
  46. Gastric Contractile Activity:
    The BER is initiated by ________ (________).
    • Basic Electrical Rhythm
    • pacemaker cells
    • Cells of Cajal
  47. Where are the Cells of Cajal (otherwise known as) located?
    • pacemaker cells
    • longitudinal muscles of stomach
    • * these cells are stimulated by the stretch
  48. Where does the most vigorous peristalsis and segmentation occur?
  49. What are the 2 ways Chyme can be delivered?
    • -small amounts to duodenum
    • -backward into stomach for further mixing
  50. Gastric emptying regulated by:
    • -neural enterogastric reflex
    • -hormonal (enterogastrone) mechanisms

    -they inhibit gastric secretion and duodenal filling
  51. What type of chyme moves quickly through duodenum?
  52. What type of chyme moves slowly through duodenum?
    fat-laden chyme, because its digested slower
  53. How long are each of the divisions of the small intestines?
    • Duodenum: 10-12 inches
    • Jejunum: 8 feet long
    • Ileum: 11 feet long
  54. Plicae cirulares:
    • deep circular folds of the mucosa and submucosa
    • forces chyme through and increase time of absorption
  55. Villi
    fingerlike extensions of mucosa
  56. Microvilli
    • brush border cells
    • tiny projections of absorptive mucosal cells' plasma membranes
    • also secrete digestive enzymes
  57. What are the cells of intestinal cypts?
    • Crypts of Lieberkuhn
    • secrete intestinal juice
  58. Peyer's patches are found where?
    • submucosa
    • Ileum
  59. What secretes alkaline mucus within the duodenum?
    Brunner's glands which neutralizes acidic chyme from stomach
  60. Falciform ligament:
    • seperates right and left lobes of liver
    • suspends liver from diaphragm and anterior abdominal wall
  61. Ligamentum teres:
    • remnant of fetal umbilical vein
    • circular
    • runs along free edge of falciform ligament
  62. When you eat, the Sphincter of Oddi is...
  63. What does the portal triad consist of?
    • bile duct
    • hepatic artery
    • hepatic portal vein
  64. Where are the portal triads found?
    each of the 6 corners of each liver lobule
  65. Hexagonal shaped liver lobules are composed of?
    hepatocyte (liver cell) plates radiating outward from central vein
  66. Liver sinusoids:
    • enlarged, leaky capillaries located between hepatic plates
    • blood from hepatic portal vein and artery come through here and empties into central vein
  67. Kupffer cells
    • hepatic macrophages found in liver sinusoids
    • they remove debris such as bacteria and worn out blood cells from blood
  68. Function of Hepatocytes:
    • 1. Production of Bile
    • 2. Processing bloodborne nutrients
    • 3. Storage of fat-soluble vitamins
    • 4. Detoxification
  69. Bile flows between _________ toward ___ ___ in the ____ _____.
    • hepatocytes
    • bile ducts
    • portal triads
  70. Bile
    • yellow-green
    • alkaline
    • bile salts
    • bile pigments
    • cholesterol
    • neutral fats
    • phospholipids
    • electrolytes
  71. Bile Salts:
    • cholesterol derivatives:
    • -emulsify fat
    • -facilitate fat and cholesterol absorption
    • -solubilize cholesterol
  72. Chief bile pigment is?
    bilirubin, waste product of heme
  73. What does the Enterohepatic circulation do with bile salts?
    recycles them
  74. Gallbladder
    • thin walled, green muscular sac on ventral surface of liver
    • stores and concentrates bile by absorbing water and ions
    • releases bile by cystic duct
  75. Acidic and fatty chyme causes...
    • duodenum to release CCK and secretin into bloodstream
    • this stimulates liver to produce bile
  76. Vagal stimulation
    causes weak contractions of gallbladder
  77. Cholecystokinin (CCK) causes:
    • gallbladder to contract
    • hepatopancreatic sphincter to relax
    • *Result: bile enters duodenum
  78. Pancreas
    • produces most digestive enzymes of any organs
    • 1200-1500mL per day
    • exocrine and endocrine gland
  79. What enzymes does the pancreas secrete?
    • 1. Typsin: polypeptides-peptides
    • 2. Lipase: fat-fatty acids
    • 3. Amylase: Carbs-glucose
    • 4. Nucleases: Nucleic acid-nucleotides
    • 5. Carboxypeptidase: polypeptides-peptides

    *part of Exocrine function
  80. Acini:
    • cluster of secretory cells
    • contain zymogen granules with digestive enzymes
  81. Insulin:
    • (Beta cells of Islets of Langerhans)
    • decreases blood sugar by removing it from blood into cells
  82. Glucagon
    • Alpha cells
    • increases blood sugar by breaking down glycogen into glucose and fat.
  83. Composition of Pancreatic Juice:
    water solution of enzymes and electrolytes
  84. Function of Pancreatic Juice:
    • Neutralizes acid chyme
    • provides optimal environment for pancreatic enzymes
    • enzymes are activated in duodenum
  85. As chyme enters duodenum...
    • -carbs and proteins are partially digested
    • -no fat digestion takes place
    • -chyme release slowly because low pH, mixing required for proper digestion
    • -substances needed provided by liver
    • -all nutrient absorption take place in small intestine
  86. Motion in small intestine:
    • -segmentation
    • -initiated by pacemaker cell (Cajal cells)
    • -Migrating Motility Complex (MMC) peristaltic activity
  87. After nutrients are absorbed by small intestine...
    meal remnants, bacteria, mucosal cells, debris are moved into large intestine
  88. How long does it take matter to get through duodenum to ileum?
    ~2 hours