The need for a circulatory system

• All organisms need to?transport?materials to where they are needed inside their tissues
  • Small organisms?(or relatively inactive animals like jellyfish) can rely on?diffusion?alone to transport oxygen, carbon dioxide and nutrients around their bodies
  • Larger organisms?have more layers of cells, so diffusion alone is insufficient for transport of materials between cells further from the exchange surface of the organism
• Circulatory systems?are systems which?transport?fluids?containing materials needed by the organism, as well as waste materials that need to be removed
  • Circulatory systems ensure that fluids containing these substances reach all of the cells in an organism?quickly enough?to supply their needs and remove waste

Humans have a closed, double circulatory system

• A?closed?circulatory system is one in which blood is?contained within a network of blood vessels
  • As opposed to an open circulatory system in which the fluid fills the body cavity e.g. as in insects
• A?double?circulatory system passes through the heart?twice?for every?one?complete circuit of the body, with blood passing through?two separate circuits?known as?pulmonary?and?systemic?circulation
  • In the?pulmonary circulatory system
    • The right side of the heart pumps?deoxygenated?blood to the?lungs?for gas exchange
    • Blood pressure is lower?in the pulmonary system; this prevents damage to the lungs
  • In the?systemic circulatory system
    • Oxygenated?blood returns to the left side of the heart from the lungs
    • The left ventricle then pumps the oxygenated blood at?high pressure?around the?body

The double circulatory system in mammals

Main Circulatory System Structures Table