What Do the Heart and Circulatory System Do?
The circulatory system works closely with other systems in our bodies. It supplies oxygen and nutrients to our bodies by working with the respiratory system. At the same time, the circulatory system helps carry waste and carbon dioxide out of the body. Hormones — produced by the endocrine system — are also transported through the blood in our circulatory system. As the body’s chemical messengers, hormones transfer information and instructions from one set of cells to another. Did you ever wonder about the process behind your beating heart? A healthy heart makes a “lub-dub” sound with each beat. Here’s what happens to make that sound: One complete heartbeat makes up a cardiac cycle, which consists of two phases. In the first phase, the ventricles contract (this is called systole, pronounced: sis-tuh-lee), sending blood into the pulmonary and systemic circulation. To prevent the flow of blood backwards into the atria during systole, the atrioventricular valves close, creating the first (
