How are the respiratory and circulatory systems similar?

The respiratory system is your lungs, and the oxygen and carbon dioxide circulate throughout the body. The circulatory system of the body is your blood vessels your blood flow stuff like that. It is similar because when you breath in the oxygen from the lungs goes into the bloodstream giving you the oxygen you need. When you exhale, all of the old air (Carbon dioxide) leaves the bloodstream and into the lungs then out your mouth. They work together in a rhythm so that you can stay healthy and maintain the air in your lungs.

Small intestine because that is the organ which absorbs nutrients

Answer target heart rate;