Which system is a subsystem of the circulatory system that includes vessels and tissues?

The lymphatic system is indeed a subsystem of the circulatory system, which plays a crucial role in the body's immune response and fluid balance. It consists of a network of lymphatic vessels, lymph nodes, and tissues that are involved in transporting lymph—an important fluid that contains infection-fighting white blood cells, as well as waste products filtered from the blood.

The lymphatic system works in conjunction with the circulatory system by maintaining fluid levels in the body, absorbing fats from the digestive system, and providing a pathway for immune cells to circulate and respond to pathogens. This close relationship emphasizes its role as a subsystem that complements the overall function of the circulatory system.

The other systems mentioned do not directly form a part of the circulatory system. The respiratory system is primarily involved in gas exchange. The endocrine system focuses on hormone regulation throughout the body, influencing various processes. The muscular system is responsible for movement and stability but does not specifically incorporate elements related to the circulation of blood or lymphatic fluids.