Heart and circulation
The heart and blood vessels that form the circulation are among the first organs that start working in a human body. And 70, 80 or 90 years later, the end of life is marked when they stop. Until then the heart will beat three billion times and pump 200 million litres of blood through the veins. The heart and circulation adapt quickly to the body's needs. The arteries and major blood vessels are flexible and muscular, and they can quickly increase or decrease in diameter to allow for changes in blood flow.