digestive system

• tissue 


  a group of cells with a similair structure or function
• organ 


  a group of tissues that work together to carry out a specific function
• organ system 


  group of organs working together to carry out a specific function
• Main nutrients in food


  • Carbohydrates
  • Protein
  • Lipids (fats)
• Digestion


  1. Large food molecules broken down into small molecules by enzymes

  2. Small molecules absorbed into bloodstream
• Main organs of the digestive system


  • Mouth
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Liver
  • Pancreas
• Mouth


  • Food chewed, enzymes in saliva begin to digest starch
• oesophagus


  • Food passes from mouth to stomach
• Stomach


  • Enzymes begin digestion of proteins, contains hydrochloric acid, churning action turns food into fluid
• Small intestine


  • Chemicals from liver and pancreas continue digestion of starch, protein and lipids
  • Small food molecules produced by digestion are absorbed into bloodstream
• Large intestine


  • Water absorbed into bloodstream, feces released from body
• Products of digestion used by body to build new carbohydrates, lipids and proteins
• Some glucose produced is used in respiration
• Enzymes


  Catalyze chemical reactions, speed them up
• Enzymes


  • Large protein molecules
  • Have a groove on their surface called the active site
  • The active site is where the substrate attaches
• Substrate


  The molecule that the enzyme breaks down
• Substrate fits into the active site


  Enzyme can break down the substrate
• Substrate does not fit into the active site


  Enzyme cannot break down the substrate
• Lock and key theory


  Enzymes are specific, the substrate must fit perfectly into the active site
• Protein digestion


  1. Proteases in stomach, pancreatic fluid and small intestine

  2. Convert proteins to individual amino acids
• Proteins


  Long chains of chemicals called amino acids
• Starch digestion


  1. Carbohydrases, specifically amylase in saliva and pancreatic fluid

  2. Break down starch into simple sugars
• Starch


  Chain of glucose molecules
• Lipid digestion


  1. Lipase in pancreatic fluid and small intestine

  2. Breaks down lipids into glycerol and fatty acids
• Lipids


  Molecule of glycerol attached to three molecules of fatty acids
• Bile


  • Made in the liver, stored in the gallbladder
  • Not an enzyme, but helps speed up lipid digestion by lipase
  • Converts large lipid droplets into smaller droplets, increasing surface area
  • Alkaline, neutralizes stomach acids in small intestine
• Small intestine


  The part of the digestive system where the products of digestion are absorbed into the bloodstream
• Small intestine


  • Very long (around 5 meters in humans)
  • Covered with millions of villi
  • Villi have micro villi that further increase surface area
  • Good blood supply to remove products of digestion
  • Thin membrane under villi for short diffusion path
• Absorption of products of digestion in small intestine


  1. Diffusion of molecules that can be absorbed this way

  2. Active transport for molecules that cannot be absorbed by diffusion
• The features of the small intestine enable a rapid rate of diffusion of the products of digestion into the bloodstream