What system is composed of a network of capillaries that returns lymph to the bloodstream?

The lymphatic system is integral to fluid balance and the immune response, playing a crucial role in returning lymph, a clear fluid that contains white blood cells, back to the bloodstream. This system consists of a network of lymphatic vessels, capillaries, and lymph nodes, all of which work together to collect and transport lymph from the interstitial spaces in tissues. As lymph circulates through this network, it is filtered by lymph nodes, where immune responses can be initiated if pathogens or foreign substances are detected. Once filtered, the lymph eventually drains into the thoracic duct or the right lymphatic duct, where it is returned to the bloodstream, specifically into the veins near the heart.

Other systems listed do not serve this particular function: the cardiovascular system primarily involves the transportation of blood; the endocrine system regulates hormonal functions; and the respiratory system is responsible for the exchange of gases. Thus, the lymphatic system is specifically designed for the collection and return of lymph, highlighting its unique role in maintaining fluid homeostasis and supporting immune health.