The Mammalian Heart (OCR AS Biology)

Heart structure

• The human heart has a mass of around 300g and is roughly the size of a closed fist
• The heart is a hollow, muscular organ located in the chest cavity
• It is protected in the chest cavity by the pericardium, a tough and fibrous sac

The human heart has four chambers and is separated into two halves by the septum

• 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 is very important for ensuring blood doesn’t mix between the left and right sides of the heart

Valves in the heart

• 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

• Valves are important for keeping blood flowing forward in the right direction and stopping it flowing backwards. They are also important for maintaining the correct pressure in the chambers of the heart
• The right atrium and right ventricle are separated by the atrioventricular valve, which is otherwise known as the tricuspid valve
• The right ventricle and the pulmonary artery are separated by the pulmonary valve
• The left atrium and left ventricle are separated by the mitral valve, which is otherwise known as the bicuspid valve
• The left ventricle and aorta are separated by the aortic valve
• 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 aorta

Coronary arteries

• The heart is a muscle and so requires its own blood supply for aerobic respiration
• The heart receives blood through arteries on its surface, called coronary arteries
• It’s important that these arteries remain clear of plaques, as this could lead to angina or a heart attack (myocardial infarction)

The coronary arteries cover the outside of the heart, supplying it with oxygenated blood