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The Digestive System

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Digestion

  • Processing of food
  • Types
    • Mechanical (physical)
      • Chew
      • Tear
      • Grind
      • Mash
      • Mix
    • Chemical
      • Catabolic reactions
      • Enzymatic hydrolysis
        • Carbohydrate
        • Protein
        • Lipid

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Digestion

  • Phases
    • Ingestion
    • Movement
    • Digestion
    • Absorption
    • Further digestion

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Digestive System Organization

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  • Gastrointestinal (Gl) tract (Alimentary canal)
    • Tube within a tube
    • Direct link/path between organs
    • Structures
      • Mouth
      • Oral Cavity
      • Pharynx
      • Esophagus
      • Stomach
      • Duedenum
      • Jejenum
      • kIleum
      • Cecum
      • Ascending colon
      • Transverse colon

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Digestive System Organization

      • Descending colon
      • Sigmoid colon
      • Rectum
      • Anus
  • Accessory structures
    • Not in tube path
    • Organs
      • Teeth
      • Tongue
      • Salivary glands
      • Liver
      • Gall bladder
      • Pancreas

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Anatomy of the Mouth and Throat

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Human Deciduous and Permanent Teeth

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Dorsal Surface of the Tongue

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The Major Salivary Glands

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Deglutition (swallowing)

  • Sequence
    • Voluntary stage
      • Push food to back of mouth
    • Pharyngeal stage
      • Raise
        • Soft palate
        • Larynx + hyoid
        • Tongue to soft palate
    • Esophageal stage
      • Contract pharyngeal muscles
      • Open esophagus
      • Start peristalsis

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Deglutition (swallowing)

  • Control
    • Nerves
      • Glossopharyngeal
      • Vagus
      • Accessory
    • Brain stem
      • Deglutition center
        • Medulla oblongata
        • Pons
    • Disorders
      • Dysphagia
      • Aphagia

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Esophagus

  • Usually collapsed (closed)
  • 3 constrictions
    • Aortic arch
    • Left primary bronchus
    • Diaphragm
  • Surrounded by
    • SNS plexus
    • Blood vessels
  • Functions
    • Secrete mucous
    • Transport food

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Peristalsis and Segmentation

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Esophagus

  • Sphincters
    • Upper
    • Lower
  • Abnormalities
    • Achalasia
    • Atresia
    • Hernia
    • Barret’s esophagus
    • Esophageal varices

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Stomach

  • Usually “J” shaped
  • Left side, anterior to the spleen
  • Mucous membrane
    • G cells – make gastrin
    • Goblet cells – make mucous
    • Gastric pit – Oxyntic gland – Parietal cells – Make HCl
    • Chief cells – Zymogenic cells
      • Pepsin
      • Gastric lipase

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Anatomy of the Stomach

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Stomach

  • 3 muscle layers
    • Oblique
    • Circular
    • Longitudinal
  • Regions
    • Cardiac sphincter
    • Fundus
    • Antrum (pylorus)
    • Pyloric sphincter
  • Vascular
  • Inner surface thrown into folds – Rugae
  • Contains enzymes that work best at pH 1-2

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Stomach

  • Functions
    • Mix food
    • Reservoir
    • Start digestion of
      • Protein
      • Nucleic acids
      • Fats
    • Activates some enzymes
    • Destroy some bacteria
    • Makes intrinsic factor – B 12 absorption
    • Destroys some bacteria

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    • Absorbs
      • Alcohol
      • Water
      • Lipophilic acid
      • B 12

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Small Intestine

  • Extends from pyloric sphincter 🡪 ileocecal valve
  • Regions
    • Duodenum
    • Jejenum
    • Ileum
  • Movements
    • Segmentation
    • Peristalsis

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Small Intestine

  • Histology
    • Intestinal glands – Intestinal enzymes
    • Duodenal glands – Alkaline mucous
    • Paneth cells – Lysozyme
    • Microvilli
    • Lacteals
    • Plica circularis
    • Smooth muscle
    • Lymphatic tissue – GALT
    • Vascular

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Small Intestine

  • Absorbs
    • 80% ingested water
    • Electrolytes
    • Vitamins
    • Minerals
    • Carbonates
      • Active/facilitated transport
      • Monosaccharides
    • Proteins
      • Di-/tripeptides
      • Amino acids
    • Lipids
      • Monoglycerides
      • Fatty acids
      • Micelles
      • Chylomicrons

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Structure of the Villi in the Small Intestine

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Small Intestine

  • Secretes digestive enzymes
    • Peptidases
      • Amino-
      • Di-
      • Tri-
    • Sucrases
    • Maltase
    • Lactase
    • Saccharidases
      • Di-
      • Tri-
    • Lipase
    • Nucleases

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Small Intestine

  • Control
  • Requires pancreatic enzymes & bile to complete digestion

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Large Intestine

  • Extends from ileocecal valve to anus
  • Regions
    • Cecum – Appendix
    • Colon
      • Ascending
      • Transverse
      • Descending
    • Rectum
    • Anal canal

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Anatomy of the Large Intestine

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Large Intestine

  • Histology
    • No villi
    • No permanent circular folds
    • Smooth muscle
      • Taeniae coli
      • Haustra
    • Epiploic appendages
    • Otherwise like rest of Gl tract

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Large Intestine

  • Functions
    • Mechanical digestion
      • Haustral churning
      • Peristalsis
      • Reflexes
        • Gastroileal
        • Gastrocolic
    • Chemical digestion – Bacterial digestion
      • Ferment carbohydrates
      • Protein/amino acid breakdown

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    • Absorbs
      • More water
      • Vitamins
        • B
        • K
    • Concentrate/eliminate wastes

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Feces Formation and Defecation

  • Chyme dehydrated to form feces
  • Feces composition
    • Water
    • Inorganic salts
    • Epithelial cells
    • Bacteria
    • Byproducts of digestion
  • Defecation
    • Peristalsis pushes feces into rectum
    • Rectal walls stretch
  • Control
    • Parasympathetic
    • Voluntary

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Liver

  • Location
    • R. Hypochondrium
    • Epigastric region
  • 4 Lobes
    • Left
    • Quadrate
    • Caudate
    • Right
  • Each lobe has lobules – Contains hepatocytes – Surround sinusoids – Feed into central vein

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Liver

  • Functions
    • Makes bile
      • Detergent – emulsifies fats
      • Release promoted by:
        • Vagus n.
        • CCK
        • Secretin
      • Contains
        • Water
        • Bile salts
        • Bile pigments
        • Electrolytes
        • Cholesterol
        • Lecithin

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Liver

    • Detoxifies/removes
      • Drugs
      • Alcohol
    • Stores
      • Gycolgen
      • Vitamins (A, D, E, K)
      • Fe and other minerals
      • Cholesterol
    • Activates vitamin D
    • Fetal RBC production
    • Phagocytosis
    • Metabolizes absorbed food molecules
      • Carbohydrates
      • Proteins
      • Lipids

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Liver

  • Dual blood supply
    • Hepatic portal vein
      • Direct input from small intestine
    • Hepatic artery/vein
      • Direct links to heart

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The Duodenum and Related Organs

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The Organs and Positions in the Abdominal Cavity

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Structures of the Alimentary Canal

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