Digestive System

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• Digestive
  System
• Processes Ingestion (food in), Movement,
  Digestion (chemical and mechanical), Absorption,
  Defecation
• Types
• 1. Chemical breakdown of large carbohydrates,
  lipids and protein into simple molecules
• 2. Mechanical chewing, muscular contraction

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C. Organization Gastrointestinal Tract and
Accessory Organs 1. GI Tract (Alimentary Canal)
mouth, pharynx, esophagus, stomach, small
intestine, large intestine 2. Accessory Organs
teeth, tongue, salivary glands, liver, gall
bladder, pancreas
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D. Histology 1. mucosa inner lining mucous
membrane 2. submucosa areolar connective
tissue binds mucosa to muscle, contains blood
and lymphatic tissue 3. muscularis skeletal
mouth, pharynx, upper esophagus, (swallowing)
smooth muscle the rest of the tract 4. serosa
outermost layer, serous fluid allows for free
gliding of the mesentery, omentum and falciform
ligament
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• Digestive Tract Anatomy and Physiology
• 1. Mouth oral or buccal cavity
• a. Tongue skeletal muscle covered with
  mucous membrane
• Extrinsic muscles outside and insert in, move
  tongue side to
• side and in and out
• Intrinsic muscles inside, speech and
  swallowing
• b. Salivary glands - 3 pairs parotid,
  submandibular, sublingual
• Saliva 99.5 H2O, .5 solutes lubrication
  and dissolving, Salivary Amylase under nervous
  control

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c. Teeth located in bony sockets of maxilla
and mandible - KNOW TYPES AND FUNCTIONS
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• Digestion in the mouth
• Mechanical Mastication (chewing)
• Chemical Salivary Amylase starts breakdown
  of starch

• Esophagus lies behind the trachea
• a. Function transports food
• b. Peristalsis muscular movements
  (involuntary) to push food through esophagus
• c. lower esophageal sphincter prevents
  backflow of HCl (heartburn)

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• Stomach J-shaped
• a. Anatomy cardia superior opening
• Fundus up and to the left
• Body large central portion
• Pyloris narrow, inferior region

b. Digestion MECHANICAL mixing
waves Peristaltic movements every
15-20 seconds, forms chyme CHEMICAL
Pepsin digests proteins, effective at
pH of 2 Gastric Lipase breaks down large
lipids (triglycerides) Controlled by
nervous and hormonal mechanisms
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• Regulation of gastric emptying Stomach empties
  all of contents into duodenum within 2-6 hours
• Carbohydrates spend less time in stomach,
  proteins more
• Vomiting forceful expulsion of contents from
  upper GI tract

• Pancreas behind stomach, secrete into duodenum
  through pancreatic duct
• a. Anatomy Islets of Langerhans and Acini
  cells, 2 types of cells
• b. Pancreatic juices
• EXOCRINE ENDOCRINE
• Acini cells Islets of Langerhans
• Produce mixture of digestive Glucagon
  (converts
• enzymes pancreatic enzymes glycogen to
  glucose)
• Multiple enzymes for digestion Insulin
  (transports
• of carbs, protein, fat glucose into cells and
  
• Regulated by nervous system changes glucose
  into
• and hormones glycogen

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5. Liver heaviest gland, supported by
falciform ligament

• Functions
• Lobules consist of hepatic cells which produce
  bile
• Destroys worn out white and red blood cells,
  bacteria and other toxins
• b. Bile yellow, brownish or olive green, pH
  of 7.6-8.6, aids in emulsification, conversion of
  fat into droplets, helps in absorption of fat

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6. Gall bladder concentrates and stores bile
until needed by small intestine
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• Small intestine most digestion and absorption
  (90) occurs here
• a. Anatomy 21 ft long in cadaver, 10 ft long
  in living (muscle tone)
• Made up of duodenum, jejunum, ileum

b. Adaptations - length, mucosa and submucosa
are modified to increase digestion and
absorption, villi and microvilli increase surface
area, circular folds
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• Digestion and absorption of major nutrients
• CARBOHYDRATES maltase, sucrase and lactase
  break disaccharides into monosaccharides,
  absorbed as such
• PROTEINS pepsin fragments proteins into
  peptides, Peptidase completes the task, absorbed
  as amino acids
• LIPIDS occurs in small intestineby pancreatic
  lipase, absorbed as monoglycerides and fatty
  acids
• NUCLEIC ACIDS done by intestinal and
  pancreatic juices

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• Large Intestine completion of absorption, makes
  vitamins, forms feces
• a. Anatomy 5 feet long, 2.5 in in diameter,
  ileocecal sphincter, appendix, ascending,
  transverse, descending and sigmoid colon
• b. Digestion, absorption, and feces formation
  MECHANICAL following meal chyme is forced into
  cecum, food intiates mass peristalsis drives
  colon contents into the rectum 3 or 4 times
  daily
• 9. Disorders of the digestive system

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