1 Double circulatory system as it is doing two jobs at a time
2 Theres the: Aorta, Inferior and superior vena cava, left vetricle, right ventricle, left atrium, right atrium, left and right pulmonary veins and artieries. Theres also a pulmony Valve and tricuspid, and bicuspic valve
3 There is deoxygenated blood ('oxygen poor') it appears 'blue' because it has travelled all around the body and come back to the heart via the vena cava - a major vein. This type of blood travels in the veins.
4 There is oxygenated blood. 'oxygen rich' as it has travelled to the lungs to gain oxygen, ready to be transported to every part of our body through the aorta
5 Valves prevent backflow of blood. Valves keep blood going in the right direction and this is especially important in the vena cava travelling up from the lower part of the body
5.1 People can be given a replacement heart but it doesnt last a lifetime.
5.1.1 People can also be given replacement valves - animals (such as pigs) last many years in humans.
184.108.40.206 Artificial valves can also be given and these are made of titanium, but they don't last as long and blood clots up around them, so people have to take medicines everyday to prevent this further problem
6 Strokes, heart attacks, heart disease and other heart problems are normally causes by blockages of the lumens of the major veins and arteries such as the Vena Cava and Aorta.
6.1 These are caused by build up of fat/ cholesterol over time. Age also contributes to this, due to the huge amount of pressure out circulatory system under goes.