The Heart

• It is divided into four chambers: two atria and two ventricles.
• The heart is made of muscle which contracts to pump blood around the body
• The heart is divided into 2 halves
• Blood flows in one direction through each half of the heart
• There are atrio-ventricular valves between the atria and ventricles. These can close to prevent backflow of blood when the ventricles contract
• There are semi-lunar valves at the bottom of the pulmonary artery and aorta to prevent backflow of blood into the ventricles when they relax
• there are tendons attached to the valves so they dont get pushed inside out.
• The left side of the heart pumps oxygenated blood to the body
• The atria have thin walls because they only pump blood to the ventricles
• The ventricles have thick muscular walls because when they contract they have to pump blood out of the heart
• The left ventricle has a thicker muscular wall than the right ventricle because it pumps blood to all parts of the body, the right ventricles only pumps blood to the lungs.
• The vena cava carries blood from the organs of the body to the right atrium
• Blood passes through the right atrioventricular valve to the right ventricle
• the right ventricle contracts, pumping blood through a semi-lunar valve into a pulmonary artery.
• The pulmonary artery carries the blood to the lungs where it is oxygenated
• The pulmonary vein carries blood back from the lungs to the left atrium
• Blood passes through the left atrio-ventricular valve in the left ventricles
• The left ventricle contracts, pumping blood through a semi lunar valve into the aorta
• the aorta carries blood from the heart to the organs of the body
• Parts of the heart :

  Semi-lunar valves

  Right side :

  Pulmonary artery

  Vena Cava

  Right Atrium

  tricuspid valve

  Right ventricle

  Left side : Aorta

  Pulmonary vein

  Left atrium

  Biscuspid valve

  Left Ventricle
• The coronary artery supplies the heart muscle with blood and oxygen
• The double circulatory system means that the blood passes through the heart twice to make a complete circuit
• What is meant by a double circulatory system?

  Blood passes twice through the heart to make a complete circuit
• the septum separates the 2 halves of the heart to stop blood mixing
• arteries have small lumen to maintain high pressure
• veins have large lumen to maintain low pressure