Digestive system

• Overview of Topics


  • Functions
  • The Digestive Process
  • Organs for Digestion
  • Phases of Digestion
  • Neural Innervation
  • Deglutition
  • HCL Production
  • Pathophysiology
• Functions


  • Prepare food for absorption and metabolism
  • Absorption
  • Elimination of wastes
• The Digestive Process


  • Ingestion
  • Secretion
  • Mixing and Propulsion
  • Digestion
  • Absorption
  • Defecation
• Organs for Digestion


  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small Intestines
  • Large Intestines
• Mouth


  • Movement of Food: Mastication
  • Accessory Organs: Teeth, Tongue, Lips and cheeks, Palate, Salivary glands
  • Secretion: Salivary amylase, Lingual lipase
  • Digestion: Initial site of carbohydrate metabolism
  • Absorption: None
• Pharynx


  • Movement of Food: Swallowing
  • Anatomy: Nasopharynx, Oropharynx, Laryngopharynx
• Esophagus


  • Movement of Food: Peristalsis
  • Anatomy: Upper esophageal sphincter, Lower esophageal sphincter
• Stomach


  • Movement of Food: Peristalsis (propulsion + retropulsion)
  • Accessory Organs: Fundus, Body, Pylorus, Pyloric Sphincter
  • Secretion: Gastric juice (HCl, Enzymes)
  • Digestion: Initial site of protein and lipid metabolism
  • Absorption: Water, ions, lipids, alcohol, aspirin
  • Stomach Cells: Mucus Cells, Parietal Cells, Chief Cells, G-Cells
• Small Intestines


  • Movement of Food: Segmentation, Migrating Motility Complex
  • Anatomy: Duodenum, Jejunum, Ileum
  • Accessory Organs: Liver, Gallbladder, Pancreas
  • Secretion: Pancreatic juice, Bile, Intestinal juice
  • Digestion: Carbohydrates, proteins, lipids, nucleotides
  • Brush Border Enzymes
  • Absorption: Carbohydrates, proteins, lipids, electrolytes, vitamins, water
• Large Intestines


  • Movement of Food: Haustral churning, Mass peristalsis
  • Accessory Organs: Cecum, Appendix, Ascending colon, Transverse colon, Descending colon, Sigmoid colon, Rectum, Internal Anal Sphincter, External Anal Sphincter
  • Secretion: Good Bacteria
  • Digestion: Carbohydrates, proteins, bile
  • Absorption: Water, ions, Vitamin B12 and K
  • End Products of Digestion: Feces
• Neural Innervation of GIT


  • Enteric
  • Autonomic
  • Gastrointestinal Reflexes
• Phases of Digestion


  • Cephalic Phase
  • Gastric Phase
  • Intestinal Phase
• Cephalic Phase


  • See, smell, taste, think of food
  • Stimulation of cerebral cortex, hypothalamus, medulla
  • Nerve impulse to facial, vagus & glossopharyngeal nerve
  • Increased salivary and gastric secretions
• Gastric Phase


  • Neural Regulation: Stimulus, Receptor, Control Center, Effect
  • Hormonal Regulation: Gastrin
• Intestinal Phase


  • Neural Regulation: Delayed gastric emptying, Activate sympathetic nervous system, Decreased motility
  • Hormonal Regulation: Cholecystokinin, Secretin
• HCL Production


  1. H+ moves out of the parietal cells into the inside of the stomach and K+ move into the cell by active transport (uses up ATP)

  2. Cl- moves out of the cell into the stomach lumen

  3. H+ and Cl- combine to form HCl
• Vagus nerve


  Glossopharyngeal nerve
• Gastric Phase


  1. Stretch and change in pH of stomach

  2. Detect stimuli and send nerve impulse

  3. Contraction of stomach muscles

  4. Increased gastric secretions
• Gastrin


  Goes to bloodstream → inside stomach → stomach cells → increase gastric secretions, close esophageal sphincter, open pyloric sphincter
• Intestinal Phase


  1. Delayed gastric emptying

  2. Activate sympathetic nervous system

  3. Decreased motility (closing of pyloric sphincter)
• Cholecystokinin (CCK)


  Increases intestinal secretions and open their pathways
• Secretin (S)


  • Increased intestinal juice (buffer chyme)
  • Contract pyloric sphincter
  • Decrease gastric secretions
• HCl Production


  1. H+ moves out of the parietal cells into the inside of the stomach and K+ move into the cell by active transport

  2. K+ will eventually move out of the cell through an ion channel

  3. H+ will react with Cl- inside the stomach to form HCl

  4. H2O and CO2 molecules inside the cell will react due to carbonic anhydrase to form H2CO3

  5. H2CO3 will dissociate into H+ and HCO3-

  6. H+ produced undergo active transport using the proton pump

  7. HCO3- will go into the bloodstream causing an alkaline tide

  8. As HCO3- moves out of the cell, Cl- will enter in exchange

  9. Cl- will leave the cell using an ion channel and move into the inside of the stomach

  10. Cl- will react with H+ to form HCl
• GERD


  A common acid-related GI disorder associated with a wide array of symptoms, the most frequent of which is heartburn and acid regurgitation resulting from the abnormal retrograde passage of gastric contents from the stomach into the esophagus
• Causes of GERD include drugs, diet, lifestyle, medical condition, pregnancy
• Symptoms of GERD include persistent heartburn, regurgitation of gastric contents, water brash, belching, hiccup, vomiting
• Pathophysiology of GERD


  Relaxation of LES, esophageal acid clearance, anatomic abnormalities, delayed gastric emptying, aggressive esophageal damage, H. pylori
• Diagnosis of GERD includes endoscopy and barium enema
• Treatment of GERD includes dietary change, medicines, surgery
• Dental caries are formed by the action of bacteria on sugars, producing acids that demineralize the enamel on teeth
• Periodontal disease is a collective term for a variety of conditions characterized by inflammation and degeneration of the gums, alveolar bone, periodontal ligament, and cementum often caused by poor oral hygiene, local irritants, or a poor "bite"
• Peptic ulcer disease is a craterlike lesion in the GI tract exposed to acidic gastric juice caused by either bacteria (Helicobacter pylori) or NSAIDs (aspirin, mefenamic acid)
• Zollinger-Ellison syndrome is a rare condition with too much gastric acid
• Diverticular disease involves saclike outpouchings of the wall of the colon (diverticula) that occur in places where the muscularis has weakened and inflamed, and if diverticula rupture, the release of bacteria into the abdominal cavity can cause peritonitis
• Colorectal cancer is associated with genetics, intake of alcohol, and diets high in animal fat and protein, and screening includes testing for blood in the feces, digital rectal examination, sigmoidoscopy, colonoscopy, and barium enema
• Hepatitis is caused by a virus that can cause chronic or acute symptoms of fever, jaundice, abdominal pain, fatigue or liver damage
• Anorexia nervosa is a chronic disorder characterized by self-induced weight loss, negative perception of body image, and physiological changes that result from nutritional depletion