3 2 The heart Unit 3 The human

3. 2 The heart Unit 3 The human circulatory system

Outline of lesson content • The structure and function of the heart

The structure of the heart The heart is a large muscular organ. The heart has four chambers: -an upper and lower chamber on the left, -an upper and lower chamber on the right.

Four chambers are divided into two halves - the right-hand side and the left-hand side. The right-hand side of the heart is responsible for pumping deoxygenated blood to the lungs. The left-hand side pumps oxygenated blood around the body.

The heart receives its own supply of blood from the coronary arteries.

• The heart contains valves to make sure the blood always flows in the right direction. • The valves are between chambers.

How the heart works The heart is made of muscle. This muscle contracts and then relaxes.

• When muscle contracts, it gets shorter. • This makes the walls of the heart chambers squeeze inwards. • This pushes blood out of the heart. The atria and ventricles work together, alternately contracting and relaxing to pump blood through your heart.

Heart valve There are valves between the upper chambers and the lower chambers. The valves only let the blood flow from the upper chamber to the lower chamber. Tricuspid valve. Located between the right atrium and the right ventricle. Mitral valve. Located between the left atrium and the left ventricle.

Heart valve There also valves in the big arteries coming out of the heart. These valves only let the blood flow out, not back in to the heart.

This is what happens during one heart beat: • The heart muscle contracts, pushing blood out into the arteries. • The heart muscle relaxes, allowing blood to flow into the heart from the veins.

Summary • The heart is made of muscle, which contracts and relaxes to pump blood around the body. • The heart contains valves to make sure the blood always flows in the right direction.

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