What system is comprised of the heart, blood vessels, and blood?

The system comprised of the heart, blood vessels, and blood is known as the circulatory system. This system plays a crucial role in transporting nutrients, oxygen, hormones, and waste products throughout the body. The heart functions as a pump, moving blood into various types of blood vessels—arteries, veins, and capillaries—that facilitate this transportation.

Understanding the structure and function of the circulatory system is essential in a fitness context, as proper blood circulation is vital for delivering oxygen and nutrients to muscles during physical activity and for removing metabolic waste products. The circulatory system works in conjunction with the respiratory system, which involves the exchange of gases, but the primary focus of the question is on the components specifically associated with circulation.

The other options refer to different systems that either have unrelated structures or functions. The respiratory system involves the lungs and airways and is responsible for gas exchange, while the cardiorespiratory system encompasses both the circulatory and respiratory systems working together during exercise but is not synonymous with the circulatory system on its own. The muscular system pertains to muscles and their functions related to movement and stability, distinct from the activities of the circulatory system.