EXTRA: CURIOSITIES

• The heart doesn't need a body. If we remove a heart from a human body, it can continue working if receive oxygen.  
  

Some curiosities about the circulatory system are: 

• The circulatory system is composed by a lot of blood vessels, arteries and capillaries. If we extend them in order, we can obtain a line of 100.000 kilometers.

• The big bodies have slower heart rates. For example, a whale has a heart rate of 5 beats per minute, while humans have a heart rate of approximate 75 beats per minute.