National League for Nursing (NLN PAX) Practice Exam

The primary function of the circulatory system is to transport nutrients and oxygen to cells throughout the body. This system plays a crucial role in maintaining homeostasis by facilitating the distribution of essential substances required for cellular metabolism. Blood, which circulates through the body via the heart and a network of vessels, carries oxygen from the lungs and nutrients from the digestive tract to the body’s tissues.

Additionally, the circulatory system is responsible for removing waste products, such as carbon dioxide and metabolic byproducts, from the cells, ensuring that they do not accumulate to toxic levels. This efficient transport mechanism underpins the overall functionality of organs and systems in the body, supporting growth, energy production, and the repair of tissues.

While respiration is associated with the exchange of gases (oxygen and carbon dioxide), it does not encompass the entirety of the circulatory system’s functions. The system indeed plays a role in hormone distribution, but that is a secondary function. The immune response is primarily handled by the lymphatic system and various immune cells, although components of the circulatory system, such as white blood cells, do participate in immune functions. Thus, the correct answer reflects the core responsibility of the circulatory system in delivering vital substances to the body's cells.