Digestive System

• The digestive system (alimentary canal/gastro intestinal tract(GI)) is the series of tube like organs that convert our meals into body fuel
• In all there's about 30 feet (9 meters) of these convoluted pipe works, starting with the mouth and ending with the anus
• Along the way, food is broken down, sorted, and reprocessed before being circulated around the body to nourish and replace cells and supply energy to our muscles
• Ingestion


  The act of taking food into the body
• Digestion


  The process of breaking down food into smaller molecules that can be absorbed and used by the body
• Absorption


  The process of nutrients being taken up from the digestive system into the bloodstream
• Assimilation


  The process of incorporating nutrients into the body
• Egestion


  The process of eliminating undigested food and waste from the body
• Movement of food through the alimentary canal


  1. Ingestion

  2. Digestion

  3. Absorption

  4. Assimilation

  5. Egestion
• The mouth


  • Digestion begins here
  • Food is chewed, moved around and moistened by saliva
  • Tongue has taste buds
  • Saliva contains water, mucus, salivary amylase and lysozyme
  • Food is churned into a bolus and swallowed into the oesophagus
• Mechanical digestion


  The physical breakdown of food into smaller pieces
• Chemical digestion


  The breakdown of food by enzymes
• Types of teeth


  • Incisors
  • Canines
  • Premolars
  • Molars
  • Wisdom teeth

  
• Incisors


  • Pointed/dagger shape
  • Poorly developed in humans, highly developed in carnivores for grasping and tearing of food
• Molars


  • Flat surface for grinding food
• Salivary amylase begins the breakdown of starch into maltose
• Oesophagus


  • Narrow muscular tube lined with epithelium cells
  • Contains mucus glands
  • Food is pushed to the stomach via peristalsis
  • Epiglottis covers the trachea to prevent food entering
• Stomach


  • Muscular bag that can stretch to store food
  • Carries out mechanical and chemical digestion
  • Contains gastric juices of mucus, hydrochloric acid and pepsin
  • Pepsin begins the breakdown of proteins
  • Churns food into chyme which is then passed to the small intestine
• Small intestine


  • Made up of duodenum, jejunum and ileum
  • Allows for complete digestion and absorption of nutrients
  • Duodenum receives bile from the liver and pancreatic juice from the pancreas to neutralize stomach acid and continue digestion
  • Ileum has adaptations like villi and microvilli to increase surface area for absorption

  
• Large intestine/Colon


  • Absorbs water and some vitamins from undigested food
  • Caecum and appendix have little function
  • Peristalsis moves undigested food to the rectum as faecal matter
• Rectum


  • Stores faecal matter temporarily before egestion through the anus
• Assimilation


  The process of incorporating nutrients (in the simplest form) into the body
• Liver


  • Filters blood, detoxifies, metabolizes proteins, lipids and carbohydrates, stores vitamins and minerals, breaks down red blood cells, produces plasma proteins, generates heat
• Homeostasis


  The maintaining of a constant internal environment despite external changes
• Blood sugar control


  • Insulin lowers blood glucose, glucagon raises blood glucose