What is the primary function of the lymphatic system?

The primary function of the lymphatic system is to filter and defend against pathogens. The lymphatic system plays a crucial role in the immune response by transporting lymph, a fluid that contains infection-fighting white blood cells, throughout the body. This system helps to identify and eliminate harmful substances, such as bacteria, viruses, and other pathogens, thus protecting the body from infections.

Lymph nodes, which are distributed throughout the lymphatic system, act as filters, trapping pathogens and other foreign particles. When pathogens are detected, the lymphatic system triggers a response from the immune system to combat these invaders. This is vital for maintaining the body's overall health and addressing any threats that may compromise it.

In contrast, the other options focus on functions that are associated with different body systems. Circulating blood is primarily the function of the circulatory system, while transporting oxygen to cells is a key role of the respiratory and circulatory systems together. Aid in digestion is primarily handled by the digestive system, which processes food and absorbs nutrients. Thus, the role of filtering and defending against pathogens distinctly defines the lymphatic system's primary function.