Digestive system

• GI tract:

  A tube open at both ends for the transit and processing of food

  
• Functional segments of the digestive system

  • Mouth
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine

  
• Accessory structures of the digestive system

  • Teeth
  • Tongue
  • Salivary glands
  • Liver
  • Gallbladder
  • Pancreas

  
• Digestion


  1. Ingestion

  2. Secretion

  3. Mixing and propulsion

  4. Mechanical digestion

  5. Chemical digestion

  6. Absorption of nutrients

  7. Defecation

  
• Mouth


  • Site of mechanical digestion (mastication or chewing)
  • Site of chemical digestion (amylase and lingual lipase)

  
• Saliva


  99.5% water, 0.5% solutes including ions, lingual lipase, and salivary amylase
• Epiglottis


  Cartilaginous, leaf-like structure that covers the trachea during swallowing to prevent fluid/food entry
• Esophagus


  Collapsible muscular tube that transports food from the pharynx to the stomach using peristalsis

  
• Gastroesophageal Reflux Disease (GERD)


  Occurs when the lower esophageal sphincter fails to close properly, allowing stomach acids to enter the esophagus and cause heartburn

  
• Regions of the stomach

  • Cardia
  • Fundus
  • Body
• Stomach


  • Site of mechanical digestion (mixing waves)
  • Site of chemical digestion (protein and fat digestion)

  
• Pancreas


  Produces pancreatic juice containing enzymes, proteases, and sodium bicarbonate for digestion
• Liver


  Heaviest gland in the body, performs functions like gluconeogenesis, breakdown of amino acids, storage of triglycerides and vitamins, synthesis of cholesterol, and detoxification
• Bile


  Composition includes water, cholesterol, bile salts, carbohydrates, lecithin, and electrolytes; functions to emulsify lipids and neutralize chyme
• Gallbladder


  Stores, concentrates, and delivers bile into the duodenum
• Parts of the small intestine

  • Duodenum
  • Jejunum
  • Ileum
• Small Intestine


  • Primary site of chemical digestion and absorption of nutrients

  
• Subdivisions of the large intestine

  • Cecum
  • Ascending/Right Colon
  • Transverse Colon
  • Descending/Left Colon
  • Sigmoid Colon
  • Rectum
  • Anus
• Large Intestine


  Final stage of digestion, site of water absorption and bacterial fermentation

  
• Defecation Reflex


  Distention of the rectal walls stimulates parasympathetic nerves, causing contraction of the descending colon and rectum, and relaxation of the internal anal sphincter
• Liver


  • Performs carbohydrate, lipid, and protein metabolism; filters drugs and hormones; stores vitamins and minerals
• Gallbladder


  Sack-like organ on the inferior/posterior surface of the liver that stores and concentrates bile

  
• Pancreas


  Produces enzymes, proteases, and sodium bicarbonate for digestion

  
• Regulation of digestion


  • Neural (enteric nervous system, parasympathetic nervous system)
  • Hormonal (gastrin, cholecystokinin, secretin, somatostatin)

  
• Phases of digestion


  1. Interdigestive

  2. Cephalic

  3. Gastric

  4. Intestinal

  
• Overview of GI tract Functions

  Mouth - mastication, swallowing

  Pharynx and esophagus - transport

  Stomach - mechanical disruption, absorption of water and alcohol

  Small intestine - chemical and mechanical digestion and absorption

  Large intestine - absorb electrolytes and vitamins

  Rectum and Anus - defecation
• Divided in to 2 major divisions:

  1. upper GI tract
  2. lower GI tract
• Functional segments:

  1. mouth
  2. esophagus
  3. stomach
  4. small intestine
  5. large intestine

  Accessory structures:

  1. teeth
  2. tongue
  3. salivary glands
  4. liver
  5. gallbladder
  6. pancreas
• Organization

  1. mouth
  2. pharynx
  3. esophagus
  4. stomach
  5. small intestine
  6. duodenum
  7. jejunum
  8. ileum
  9. large intestine
  10. cecum
  11. ascending colon
  12. transverse colon
  13. descending colon
  14. sigmoid colon
  15. rectum
  16. anus
• 6 basic processes of digestive system

  1. ingestion
  2. taking food into mouth
  3. secretion
  4. release of water, acids, buffers, and enzymes into GI tract
  5. mixing and propulsion
  6. churning and propelling food through GI tract
  7. digestion
  8. mechanical
  9. chemical (catabolic rxn)
  10. absorption of nutrients
  11. passage of nutrients from GI tract into blood or lymph for cell distribution
  12. defecation
  13. elimination of feces