What is the main function of the lymphatic system?

The main function of the lymphatic system involves the removal of excess proteins, as well as interstitial fluid, from the interstitium. This process is crucial because, during normal physiological functions, some proteins leak from blood capillaries into the surrounding tissues. The lymphatic system collects this excess fluid, along with proteins, and returns them to the cardiovascular system. This not only helps maintain fluid balance in the body but also plays a significant role in the immune response by filtering lymph through lymph nodes, where harmful substances can be identified and eliminated.

In this context, the other options do not accurately describe the primary role of the lymphatic system. The transport of proteins through blood capillaries, return of blood from the interstitium to systemic circulation, and transportation of blood from the heart to tissues all relate more to the circulatory system rather than the lymphatic system specifically. The lymphatic system's unique function is its ability to manage protein levels in the interstitial spaces, hence its critical role in fluid homeostasis and immune functioning.