Which of the following is NOT a function of the circulatory system?

The circulatory system plays several critical roles in the body, including transportation, protection, and regulation.

Transportation is one of the primary functions of the circulatory system, as it is responsible for moving blood throughout the body, which carries oxygen, nutrients, hormones, and waste products to and from cells.

Protection involves the immune response mediated by the circulatory system. Blood contains white blood cells and antibodies that protect the body from infections and foreign invaders.

Regulation refers to the circulatory system's role in maintaining homeostasis, including regulating body temperature and pH levels as blood flow adjusts according to the body’s needs.

Respiration, while closely related to the exchange of gases, is not a direct function of the circulatory system. Instead, respiration primarily involves the respiratory system, which manages the intake of oxygen and the expulsion of carbon dioxide. The circulatory system does assist by transporting oxygen from the lungs to the body's tissues and carbon dioxide from the tissues back to the lungs, but the primary process of respiration itself is separate from the circulatory functions. Thus, indicating that respiration is not a fundamental function of the circulatory system is accurate.