Body Systems: The Respiratory and Circulatory Systems - 6-Pack

Every second of every day you do two things to stay alive. You might not even know you’re doing them. You breathe. Your heart also pumps blood. You don’t think about these things because your respiratory and circulatory systems work automatically. In this book, you’ll read about these systems and how they work. You’ll also find out how knowing about these systems can help you train for a sport.