circulatory systems

• reasons why multicellular organisms needs a transport system:

  • have a low surface area to volume ratio
  • high metabolic rate (the speed at which chemical reactions take place in the body).
  • A lot of them are very active meaning a large number of cells are all respiring very quickly, so they need a constant, rapid supply of glucose and oxygen. Carbon dioxide also needs to be removed from cells quickly.
• The circulatory system in mammals uses blood to carry glucose and oxygen around the body. It also carries hormones, antibodies (to fight disease) and waste products (like CO2)
• single circulatory system 


  blood only passes through the heart once for each complete circuit of the body.
• fish's single circulatory system

  A) rest of body

  B) heart

  C) gills

  D) oxygenated blood

  E) deoxygenated blood

  
• double circulatory system


  blood passes through the heart twice for each complete circuit of the body.
• • Mammals have a double circulatory system.
  • The heart is divided down the middle, the right side of the heart pumps blood to the lungs (to pick up oxygen).
  • From the lungs it travels to the left side of the heart, which pumps it to the rest of the body.
  • When blood returns to the heart, it enters the right side again.
• • our circulatory system is really two linked loops. One sends blood to the lungs - this is called the pulmonary system, and the other sends blood to the rest of the body. this is called the systemic system.
• The advantage of the mammalian double circulatory system is that the heart can give the blood an extra push between the lungs and the rest of the body. This makes the blood travel faster, so oxygen is delivered to the tissues more quickly.
• closed circulatory system 


  the blood is enclosed inside blood vessels.
• All vertebrates (e.g. fish and mammals) have a closed circulatory system.
• In fish, the heart pumps blood into arteries. These branch out into millions of capillaries. Substances like oxygen and glucose diffuse from the blood in the capillaries into the body cells, but the blood stays inside the blood vessels as it circulates. Veins take the blood back to the heart.
• open circulatory system 


  blood isn't enclosed in blood vessels all the time.

  Instead, it flows freely through the body cavity.
• • An insect's heart is segmented.
  • It contracts in a wave, starting from the back, pumping the blood into a single main artery.
  • That artery opens up into the body cavity.
  • The blood flows around the insect's organs, gradually making its way back into the heart segments through a series of valves.
  • The circulatory system supplies the insect's cells with nutrients, and transports things like hormones around the body.
  • It doesn't supply the insect's cells with oxygen though - this is done by a system of tubes called the tracheal system.