The Mammalian Heart (Cambridge O Level Biology)

• The heart is labelled as if it was in the chest so what is your left on a diagram is actually the right-hand side and vice versa
• The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs
• The left side of the heart receives oxygenated blood from the lungs and pumps it to the rest of the body
• Blood is pumped into the heart in veins and away from the heart in arteries
• The two sides of the heart are separated by a muscle wall called the septum
• The heart is made of muscle tissue which is supplied with blood by the coronary arteries

Exterior heart structure diagram

The exterior view of the heart shows coronary arteries across the surface; these supply blood to the heart muscle itself

Interior heart structure diagram

The interior view of the heart allows the four chambers to be seen clearly

• The ventricles have thicker muscle walls than the atria as they pump blood out of the heart and so need to generate a higher pressure
• The left ventricle has a thicker muscle wall than the right ventricle as it has to pump blood at high pressure around the entire body, whereas the right ventricle pumps blood at lower pressure to the lungs
• The septum separates the two sides of the heart and prevents the mixing of oxygenated and deoxygenated blood

The structure of the heart shows the different valves

The function of valves

• The basic function of all valves is to prevent blood from flowing backwards
• There are two sets of valves in the heart:
  • The atrioventricular valves separate the atria from the ventricles
  • These valves are pushed open when the atria contract but when the ventricles contract they are pushed shut to prevent blood from flowing back into the atria
  • The semi-lunar valves are found in the two blood arteries that come out of the top of the heart
  • They are unusual in that they are the only two arteries in the body that contain valves
  • These valves open when the ventricles contract so blood squeezes past them out of the heart, but then close to avoid blood flowing back into the heart