Circulatory systems

• Circulatory system

  System that transports fluids containing oxygen, nutrients and waste
• Types of circulatory systems

  • Single circulatory system
  • Double circulatory system
• Single circulatory system


  • Blood passes through the heart once during one complete circuit of the body
• Double circulatory system


  • Blood passes through the heart twice during one complete circuit of the body
• Fish have a single circulatory system while mammals have a double circulatory system
• Single circulatory system in fish

  1. Deoxygenated blood is pumped to the gills from the heart

  2. Gills are the exchange site where oxygen and carbon dioxide are exchanged with the atmosphere and the blood

  3. Oxygenated blood flows from the gills to the rest of the body

  4. Blood travels through the capillaries in organs, delivering oxygen and nutrients

  5. Blood returns to the heart
• Double circulatory system in mammals

  1. Blood passes through the heart twice during a single circuit of the body

  2. Left side contains oxygenated blood, right side contains deoxygenated blood

  3. Blood in the right side of the heart leaves and travels to the lungs

  4. Blood returns to the left side of the heart before being pumped around the rest of the body

  5. Blood that has just passed through an organ goes straight back to the heart, not to another organ (except hepatic portal vein)
• Advantages of double circulation

  • Maintains higher blood pressure and average speed of flow
  • Allows for efficient exchange of nutrients and waste with surrounding tissues
• Types of circulatory systems

  • Closed circulatory system
  • Open circulatory system
• Closed circulatory system


  • Blood is pumped around the body and is always contained within a network of blood vessels
• Open circulatory system


  • Blood is not contained within blood vessels but is pumped directly into body cavities
• Humans have a closed double circulatory system
• Circulatory system in insects

  1. Tubular heart in the abdomen pumps haemolymph into the dorsal vessel

  2. Dorsal vessel delivers the haemolymph into the haemocoel (body cavity)

  3. Haemolymph surrounds the organs and eventually reenters the heart via one-way valves called ostia

  4. Oxygen is delivered directly to their tissues via tracheae (a system of tubes) that connect directly to the outside
• Insects are able to survive with this less efficient circulatory system because oxygen is delivered directly to their tissues via tracheae