Describe the flow of blood through the human circulation

Blood needs to circulate around the body in order to supply organs with nutrients and oxygen and to remove waste. Blood is oxygenated in small, one cell thick vessels in the lungs. These flow together to form the pulmonary veins. The pulmonary veins allow blood to flow into the heart. First, the oxygenated blood flows into the left atrium, from which it is pumped into the left ventricle through the mitral valve during diastole. During systole, the left ventricle contracts and the blood exits the heart via the aortic valve and enters the aorta. This splits up into a complex network of arteries that form the peripheral arterial circulation. These allow a distribution of nutrients and oxygen to all tissues, the blood is deoxygenated and enters the peripheral venous circulation to move back to the heart. The peripheral venous circulation of the lower limbs enters the inferior vena cava, the blood from the head and upper limbs enter the superior vena cava. Both enter into the right atrium. The right atrium contracts at the end of diastole moving the blood through the tricuspid valve into the right ventricle. During systole, the right ventricle contracts pumping the deoxygenated blood via the pulmonary valve through the pulmonary arteries into the lungs. Here the cycle repeats.