Heart

• heart cycle step 1 


  Blood enters the heart through the atria
• the heart cycle step 2

  the atria contract and force blood into the ventricles
• the heart cycle step 3


  the ventricles then contract and force blood out of the heart
• the heart cycle step 4


  valves make sure the blood flows in the correct direction
• what is the natural resting heart rate controlled by?


  the natural resting heart rate is controlled by a group of cells located in the right atrium which act as a place maker
• the heart pumps blood around the body in a double circulatory system
• the left and right atria ,which receive blood from the veins
• the left and right ventricles ,pump the blood out into the arteries
• arteries 


  they take blood from your heart to your organs
• arteries


  thick walls made from muscle and elastic fibres
• veins


  take blood from your organs to your heart
• veins


  thinner walls and valves to prevent back flow
• capillaries


  allow substances needed by the cells to pass out of the blood
• capillaries


  allow substances produced by the cells to pass into the blood
• capillaries


  narrow ,thin -walled blood vessels