Digestive System Notes Anatomy by bhangrawala06

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									                                     Digestive System
   Digest: break down food into fragments
   Absorb: taking in fragments through blood
   Alimentary Canal (food passes through)
     30 feet long in cadavers mouth, pharynx, esophagus, stomach, small intestine,
       large intestine, and anus
     Canal is open at both ends
   Digestive Process
     Ingestion (mouth)
     Propulsion- moves food
        Swallowing/peristalis
     Mechanical digestion (no enzymes)
        Chewing, saliva, churning in stomach, segmentation in intestines
     Chemical digestion (enzymes)
        Begins in mouth, finished in small intestine
     Absorption: passage of products into blood/lymph-small intestine
     Defecation: elimination through anus
   Functional concepts
     Sensors are located along the GI (gastrointestinal) tract & respond to stimuli such
       as stretching of organ wall, ph, osmolarity and presence of substrates or products
        Activate or inhibit glands that secrete into lumen (hole in center of organ)
        Mix lumen contents and move them along GI tract
     Control systems can be intrinsic or extrinsic; have own nerve plexuses
       (arrangements) or CNS centers (central nervous system)
   Abdominopelvic cavity:
     Peritoneum (serous membrane)
        Visceral peritoneum: covers external surface of most digestive organs
        Parietal peritoneum: lines walls of abdominopelvic cavity
        Peritoneal cavity separates the 2 peritineums
            Mesentary: double layer of peritoneum extends from digestive organs to
               body wall; contains blood and lymphatic vessels, and nerves
   Histology:
     4 main layers of entire alimentary canal (from lumen outward)
        Mucosa: secrete, absorbs, protects; simple columnar epithelium with goblet
           cells
        Submucosa: contains blood, lymphatic vessels, and nerves
        Muscularis Externa: segmentation and peristalis
        Serosa (adventitia): protective outermost layer; replaced by adventitia in the
           esophagus
   Functional Anatomy
     Mouth- only part is involved in ingestion
        Accessory organs: teeth, salivary lands, tongue
        Swallowing- mechanical and chemical digestion
        Oral cavity: stratified squamous epithelium
        Deglutition: swallowing
     Palate
     Hard palate: palantine and maxillae bones
     Soft palate: skeletal muscle; closes off nasopharynx
     Uvula: fingerlike projection
   Tongue
     Taste buds, glands, skeletal muscle, grips food, makes it with saliva to form
        bolus
         Lingual frenulum- holds tongue to floor of mouth
   Salivary glands: secretes saliva
     Purposes: Cleanses, Dissolves, Moistens/forms bolus, Enzymes
     Mucous- produces mucus
     Serous cells- produce enzymes and saliva’s ions
     Saliva: mostly H2O, also contains electrolytes, amylase, mucin, lysozyme,
        IgA, metabolic wastes
     Intrinsic gland: constantly secretes to keep mouth moist
     Extrinsic gland: release saliva when food is in mouth
     1000-1500 ml per day
   Teeth
     Masticate: chew, tear, and grind
     Primary dentition: baby teeth, 20
     Permanent dentition: adolescence 32
         3rd molars (wisdom teeth)- 17-25 years old
     Incisors: cutting
     Canines: tearing
     Premolars: grinding/crushing
     Molars: grinding/crushing
     Crown: exposed part of tooth above gum
     Enamel: hardest substance in body- calcium, hydroxyl apatite crystals
     Root: embedded in jawbone
     Neck: connects rood and crown
     Dentin: bonelike; under enamel-surrounds pulp
     Cavities (caries): decay of enamel
     Calculus: plaque
   Pharynx (throat)
     Stratified squamous epithelium; mucus gland; skeletal muscle
   Esophagus: collapsed when food isn’t being moved; has all 4 layers, switches
    epithelium; has both skeletal and smooth muscle
     Heartburn: gastric juices flow back into esophagus
   Stomach (storage tank)
     Food converted into chime
     Can hold up to one gallon of food
     Rugae: large, longitudinal folds
         Regions:
             Cardiac: “near the heart”, where food enters from esophagus
             Fundus: dome shaped part, beneath diaphragm
             Body: mid-portion
             Pyloric: funnel shaped
                 Pyloric sphinter: controls stomach emptying into small intestine
     Greater/Lesser Curvatures
         Gastric pits: lead into gastric glands that secrete gastric juices
         Glands in stomach- produce a special mucus, secrete HCl (for pepsin) and
            intrinsic factor (for vit. B12), produce pepsinogen, release hormone
         Mucosal barrier protects the stomach from the low PH and enzymes that
            could digest the stomach itself
         Protein digestion occurs in stomach
         Plasticity: stomach can be stretched, usually empties 4 hours after meal
   Small intestine: major digestive organ, most absorption happens here
     Gross anatomy: 6-7 meters long (20 feet) in cadaver, 6 ft in living organ
        because of muscle tone
     3 regions
         Duodenum: shortest; bile duct, pancreatic duct, duct from liver
         Jejunum: middle region
         Ileum: joins large intestine at ileocecal valve
     Microscopic adaptations:
         Plicae circulares- mucosa and submucosa folds, mix chime
         Villi- fingerlike projections, help absorb and move lymph
         Microvili: tiny projections of plasma membrane, brush border; enzymes
            and absorption
         Intestinal crypts: secrete int. juice
         Paneth cells: secrete lysozyme
         Peyers patches: have lymphoid medules
   Liver
     Produces bile which breaks up fat (emulsifier)
     Located within the rib cage
     4 primary lobes/regions
     Bile leaves through common hepatic duct and combines with cystic duct of
        gall bladder to go to duodenum
   Bile: yellow-green, salts, pigments, cholesterol, neutral fats, phospholipids,
    electrolytes
     Belirubin: main bile pigment
   Gallbladder: green muscular sac on inferior side of liver; stores bile and empties
    into cystic duct.
   Pancreas: produces many enzymes which it releases into duodenum pancreatic
    juice.
     Also has endocrine-function: islets of langerhans release insulin and glycogen
        (hormones)
   Large Intestine: greater diameter than small int., shorter in lengeth
     Absorbs water and eliminates indigestible food residues as feces
     3 unique gross anatomy features:
         Teniae coli: 3 bands of smooth muscle in muscularis
         Haustra: pocket like sacs
       Epipolic appendages: small, fat-filled pouches of visceral peritoneum that
        hang from surface
   Divisions and Regions:
     Cecum: saclike, 1st part; appendiz attaches here
     Colon: ascending, transverse, desending, sigmoid
     Rectum: has 3 folds called rectal valves
     Anal canal: lies external to abdominopelvic cavity: opens to anus, has 2
        sphincters
   Microscopic anatomy:
     Simple columnar epith. Except for anal canal (which is strat. Squamous)
     No villi or cells that secrete enzymes
     Large number of goblet cells: make mucus
   Anal canal: stratified squamous epith.
     Food remains in large int. for 12-24 hours
     No digestion occurs here
   Not necessary for life, colon can be removed and ileum brought out to
    abdominal wall.
   Ileoanal juncture: links ileum to anal canal
   Defecation reflex: as feces are pushed into anal canal, messages are sent to the
    brain. the brain decides if the external anal sphincter will open (skeletal
    muscle, voluntary)

								
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