What primarily comprises the circulatory system?

The circulatory system is primarily comprised of the heart and blood vessels. This system is responsible for transporting oxygen, nutrients, hormones, and waste products throughout the body. The heart serves as the pump that circulates blood, while the blood vessels include arteries, veins, and capillaries that provide the pathways for blood flow.

Understanding the components of the circulatory system is essential as it highlights the role these elements play in maintaining bodily functions. The heart's rhythmic contractions drive blood through the vessels, ensuring that all parts of the body receive the necessary substances for survival and function. This system is vital for both nutrient delivery and waste removal, facilitating the overall homeostasis in the body.

In contrast, the other options refer to systems and structures that do not constitute the circulatory system. Muscles and tendons are part of the muscular system, the brain and spinal cord belong to the nervous system, while glands and hormones pertain to the endocrine system. Each of these systems has distinct functions and components, separate from those of the circulatory system.