Which of the following is NOT part of the lymphatic system?

Veins are not considered part of the lymphatic system; rather, they are integral components of the circulatory system. The circulatory system is responsible for transporting blood throughout the body, while the lymphatic system primarily functions to manage fluid balance, filter out pathogens, and support immune function.

In contrast, the spleen, lymph nodes, and tonsils are all essential components of the lymphatic system. The spleen helps filter blood and supports immune response, lymph nodes act as filters for lymphatic fluid and house immune cells, and the tonsils serve as the first line of defense in the immune system, particularly against pathogens entering through the mouth and nose. Thus, the distinction lies in the specific roles and elements that comprise each system.