Describe the course of blood through the heart and lungs, explaining how it becomes oxygenated.

Considering the heart has 4 distinct chambers - for this question it's best to start in the right atrium. (Supported by a diagram) Deoxygenated blood is returned to the right atrium from the rest of the body via the vena cava (inferior and superior). It then passes into the right ventricle via the tricuspid valve, before leaving for the lungs via 4 pulmonary arteries (two for each lung) as the heart contracts. At the lungs, the blood 'picks up' oxygen at the alveolar cell surface and 'drops off' waste carbon dioxide. The blood is now oxygenated and returns to the left side of the heart at the left atrium via 2 pulmonary veins. It then passes into the left ventricle via the bicuspid valve. Contraction of the heart then forces blood out of the atrium and it is then circulated to the body tissues to be used in metabolism. The cycle then starts again.