The Mammalian Heart

• The heart is a hollow, muscular organ located in the chest cavity.
• It has a mass of around 300g and is roughly the size of a closed fist.
• It is protected in the chest cavity by the pericardium, a tough and fibrous sac.
• The heart is divided into four chambers. The two top chambers are atria and the bottom two chambers are ventricles.
• The left and right sides of the heart are separated by a wall of muscular tissue, called the septum. The portion of the septum which separates the left and right atria is called the interatrial septum, while the portion of the septum which separates the left and right ventricles is called the interventricular septum.
• The septum ensures that blood does not mix between the left and right sides of the heart.
• There are two blood vessels bringing blood to the heart; the vena cava and pulmonary vein.
• There are two blood vessels taking blood away from the heart; the pulmonary artery and the aorta.
• Heart valves are important for:

  • Keeping blood flowing forward in the right direction and stopping it flowing backwards.
  • Maintaining the correct pressure in the chambers of the heart
• The right atrium and right ventricle are separated by an atrioventricular valve known as the tricuspid valve.
• The left atrium and left ventricle are separated by an atrioventricular valve known as the bicuspid valve.
• The right ventricle and the pulmonary artery are separated by a semi-lunar valve known as the pulmonary valve.
• The left ventricle and aorta are separated by a semi-lunar valve known as the aortic valve.
• The valves in the heart:

  • Open when the pressure of blood behind them is greater than the pressure in front of them
  • Close when the pressure of blood in front of them is greater than the pressure behind them
• The heart is a muscle and so requires its own blood supply for aerobic respiration.
• The heart receives blood through arteries on its surface. These are called coronary arteries.
• It is crucial that the coronary arteries remain clear of plaques, as this could lead to angina or a heart attack (myocardial infarction).