In the 2nd century, the ancient physician Galen wrote that blood is created in the liver from ingested food and flows to the right side of the heart. He thought some of it flows then to the lungs where it gives off vapors, and some flows through pores into the left side of the heart, where it gains "vital spirits". Several arteries flow into the base of the brain, where those vital spirits are changed to animal spirits before being distributed to the rest of the body through hollow tubes called nerves. In the body tissues, blood is consumed. Amazingly, this canon held for nearly 1500 years, with only a few overlooked objections in the 1200s from Arab physician Ibn al-Nafis. (Nafis looked for the pores connecting the sides of the heart and couldn't find them; he also elucidated the pulmonary circulation.) In 1628, William Harvey realized something was amiss with this thinking. Now you can duplicate the process by which Harvey determined that blood flows through the body in a closed loop. Take your resting pulse and heart rate at rest. Recall the average stroke volume of a healthy individual. a) About how long will it take your heart to pump your entire body weight in blood? (10 pts) (you can estimate all of these numbers, just use values for the average human) b) Under Galen's version of the circulation, how much new blood would the liver need to produce each day? (10 pts)

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