Describe the structure of the human heart and how the blood is pumped by the heart.

The heart can be described as a double pump system. It consists of 4 main chambers (sections) - 2 atria and 2 ventricles split into left and right. The atria have relatively thin walls whereas the ventricles have thicker walls, the left ventricle is more muscular than the right. The easiest way to look at the blood flow of the heart is to start from the right side of the heart going through to the left. The blood flows into the right atrium via the superior and inferior vena cava, the atrium passively fills up whilst the tricuspid valve is closed. The tricuspid valve opens and the right atria contracts pushing the blood into the right ventricle. The tricuspid valve closes again, with the pulmonary valve closed the right ventricle contracts increasing pressure within the ventricle, then the pulmonary valve opens to allow the blood to be pumped to the lungs via the pulmonary arteries. Gaseous exchange takes place in the lungs and oxygenated blood returns to the left side of the heart via the pulmonary veins. Similarly to the right hand side the left atrium fills with blood whilst the bicuspid (mitral) valve is closed, the atria contracts to squeeze the blood into the left ventricle. The left ventricle contracts with both valves closed to increase pressure and then the aortic valve opens to allow the blood to flow through the body via the aorta and great vessels.