Heart

• The heart is a double circulatory system
• Right Ventricle pumps deoxygenated blood to the lungs to take in oxygen, the blood then returns to the heart.
• The left ventricle pumps oxygenated blood around all the other organs of the body
• Arteries have thick walls with elastic tissue which allows them to stretch when pumped by the heart
• Veins have thinner walls than arteries as they do not need to be able to cope with high pressure from the heart
• Capillaries are very thin so that substances can diffuse easily across their walls into cells
• The heart has valves to prevent backflow of blood
• Pulmonary Circuit

  Vena Cava -> Right Atrium -> Tricuspid Valve -> right ventricle -> Pulmonary artery -> Lungs
• Bodily Circuit

  Lungs -> Pulmonary Vein -> Left Atrium -> Bicuspid valve -> Left Ventricle -> Aorta
• Resting heart rate is controlled by a group of cells in the right atrium called pacemaker cells