9.1) Transport in animals

9.1) Transport in animals


The blood, pumped by the heart, travels all around the body in blood vessels. It leaves the heart in arteries and returns in veins. Valves, present in the heart and veins, ensure a one-way flow for the blood, as blood enters an organ, the arteries divide into smaller arterioles, which supply capillaries. In these vessels the blood moves much more slowly, allowing the exchange of materials such as oxygen and glucose, carbon dioxide and other wastes. Blood leaving an organ is collected in venules, which transfer it onto larger veins.


Single circulation of fish:

  • Simplest circulatory systems of all vertebrates.
  • A heart, consisting of one atrium (collecting chamber) and one ventricle (ejection chamber), sends blood to the gills where it is oxygenated. The blood then flows to all the parts of the body before returning to the heart.
  • Known as a single circulation because the blood goes through the heart once for each complete circulation of the body.
  • This system is inefficient because blood pressure is lost when the blood passes through capillaries in the gills


Double circulation of mammals:

  • The blood passes twice through the heart during one complete circuit.
  • Once on its way to the lungs (pulmonary circulation) and again on its way to the body (systemic circulation)
  • Advantage of maintaining a high blood pressure to all the major organs of the body.
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