Digestive System

• • Food provides our cells with energy (glucose for cellular respiration) nutrients for cell reactions and allows us to build larger molecules (EG calcium, proteins, etc.)
• • Food is digested so molecules are small enough to enter our cells
• • Function: take in food, break it down, supply nutrients and excrete waste
• Phases of Digestion

  1. Ingestion
  2. Movement
  3. Mechanical and Chemical 
  4. Adsorption
  5. Elimination
• Mechanical (physical) - Begins in the mouth, chew, tear, grind
• Chemical - Begins in the mouth, enzymatic reactions to improve digestion of carbohydrates, proteins and lipids
• Digestive Tract - long tube with openings on each end, lined with epithelial tissue: mouth, esophagus, stomach, large intestine, small intestine, anus
• Accessory organs - Produce enzymes and fluids that aid in digestion: liver, pancreas, gallbladder
• Mouth - teeth mechanically break down food into small pieces, saliva made by epithelial tissue begins chemical digestion. Saliva contains enzymes including amylase which breaks down starch, food forms a bolus (moistened ball of food)
• Pharynx - short tube shared with the digestive and respiratory system, air and food pass through. Epiglottis is a flap- like structure at the back of the throat that closes over the trachea preventing food from coming into the airways when we swallow
• Esophagus - 20cm long, moves food from the throat to the stomach using peristalsis, Heartburn is caused from stomach acid re entering the esophagus. Sphincter on top of the stomach opens up when it shouldn't be.
• Peristalsis: waves of smooth muscle contractions stimulated by the presence of food.
• Stomach - Muscular bag that churns food, mixes food with digestive juices that contain enzymes that break down proteins and lipids, Acid (HCl) in the stomach kills bacteria, food in the stomach is called the chyme
• Small  Intestine - roughly 6m long, nutrients from the food pass into the bloodstream through small intestine walls, lining of intestine walls has finger-like projections called villi to increase surface area (covered in microvilli)
• Large intestine - 1.5 m long, reabsorbs water from small intestine material and concentrates waste, contains bacteria that help break down waste, waste is excreted through the rectum and out the anus
• • Colitis/Crohn’s Disease (IBS) - inflammation of large intestine, symptoms: cramps, diarrhea, weight loss
• Liver - affects digestion by producing bile, bile helps digest fats, filters out toxins and waste including drugs and alcohol and poisons
• Gallbladder - Stores bile from the liver, releases into small intestine, fatty diets cause gallstones
• Pancreas - produces digestive enzymes to digest fats, carbohydrates and proteins, regulated blood sugar by producing insulin
• Diabetes

  Type 1 - not enough insulin is being made by the pancreas. Blood sugar levels are not controlled

  Type 2 - insulin signal is ignored, if sugar level is too high, blood vessels can be damaged, too low = lose consciousness
• Top sphincter : esophageal

  Bottom sphincter: pyloric sphincter
• Small Intestine

  There are 3 main sections

  1. Duodenum - ALL chemical digestion of accessory organs! Shortest and widest of the 3 regions
  2. Jejunum - SOME chemical digestion and some absorption takes place here (2.5m)
  3. Ileum - Absorption of nutrients (3m)
• Pepsin is a stomach enzyme that serves to digest proteins found in ingested food.
• Lipase is a type of digestive enzyme or "digestive juice."
• Amylase is an enzyme, a type of protein that helps your body break down carbohydrates.