Digestive

• Digestive System


  The system responsible for the digestion and absorption of food and other nutrients in the body

  
• The Digestive System has 6 Functions

  
• Tunic Layers of Organs in Alimentary Canal

  • Submucosal Nerve Plexus: Controls Glandular Secretions
  • Myenteric Nerve Plexus: Controls Motility of Smooth Muscle
• Anatomy of Each Organ in Alimentary Canal

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine (Colon)

  
• Anatomy of Each Accessory Digestive Organ

  • Teeth
  • Salivary Glands
  • Pancreas
  • Liver
  • Gallbladder

  
• Physiology of all Digestive Organs

  • pH of each organ
  • Nutrients digested in each organ
  • Secretions (enzymes, bile, mucus, etc.) produced/released

  
• Organization of Digestive System

  • Peritoneum: serous membranes of abdominal cavity
  • Peritoneal cavity: fluid-filled space to lubricate organs
  • Mesentery: double layer of peritoneum that extends from body wall to digestive organs
  • Intraperitoneal (peritoneal) organs: organs located within the peritoneum
  • Retroperitoneal organs: located outside, or posterior to, the peritoneum

  
• Mastication


  Chewing food to increase surface area and produce a bolus
• Deglutition


  Swallowing a bolus; includes buccal phase (voluntary) and pharyngeal-esophageal phase (involuntary)
• Peristalsis


  Wave-like muscular contraction through GI tract; begins at esophagus
• Pyloric Pump


  Emptying of ~3 ml of chyme from stomach; increases mixing
• Segmentation


  Massage of chyme in small intestine to increase mixing and digestion/absorption
• Stimulation of Stomach


  Cephalic, Gastric, and Intestinal Phases
• Catabolism


  Large molecules -> small molecules
• Enzymatic Hydrolysis


  Water + enzymes are used to break down molecules into smaller ones
• Digestion in Mouth


  Carbohydrates -> salivary amylase -> carbohydrates

  
• Digestion in Stomach


  Proteins -> HCl, pepsin -> dipeptides and polypeptides

  
• Digestion in Duodenum


  1. CHO -> pancreatic amylase -> disaccharides -> simple sugars (glucose, fructose, galactose)

  2. Polypeptides & dipeptides -> pancreatic proteases -> dipeptides and amino acids

  3. Fats -> bile -> emulsified fats -> pancreatic lipase -> fatty acids + glycerol

  
• Digestion of DNA and RNA

  DNA and RNA -> DNAases and RNAases -> nucleotides

  
• Absorption of Simple Sugars and Amino Acids

  Absorbed into intestinal capillaries via facilitated diffusion and co-transport (coupled with Na+)

  
• Absorption of Fats


  Fatty acids + Glycerol -> bile salts -> micelles -> chylomicrons -> lacteals (lymphatic vessels)

  
• Micelles


  Fat droplets with bile salts
• Chylomicrons


  Protein-coated micelles
• SNS


  Inhibits GI tract activity
• PNS


  Stimulates GI tract activity
• Gastrin


  Hormone that stimulates gastric activity
• Secretin / Cholecystokinin


  Hormones that inhibit gastric activity and stimulate intestinal, pancreatic, liver, gallbladder activity, and open hepatopancreatic ampulla