Circulatory Systems (DP IB Biology)

Comparing Single & Double Circulation

Differences between single circulation in bony fish and double circulation in mammals

• Both fish and mammals have a closed circulatory system

  • This means blood is contained within a system of blood vessels

• Bony fish have single circulation

  • Blood moves through the heart once during each complete circuit

  • The heart has two chambers

  • It enters the heart from the body before being pumped to the gills

  • Here blood is oxygenated before moving to the rest of the body

Single circulation diagram

Bony fish have single circulation

• Mammals have double circulation

  • This means blood flows through the heart twice for each complete circuit of the body

  • The heart has four chambers; two on the right and two on the left

  • The right side of the heart pumps deoxygenated blood to the lungs for gas exchange; this is pulmonary circulation

  • Blood then returns to the left side of the heart, so that oxygenated blood can be pumped at high pressure around the body; this is systemic circulation

Double circulation diagram

Mammals have double circulation

• The main advantages of the mammalian double circulation system include:

  • Keeping oxygenated and deoxygenated blood separate, so that cells can receive blood with high oxygen levels for aerobic respiration

  • Maintaining a high pressure for the transport of oxygenated blood to every part of the body

  • Pumping blood at a lower pressure in the lungs so that delicate blood vessels are not damaged