Which body system is primarily responsible for defending against infection and disease, including returning tissue fluid to the bloodstream?

Which body system is primarily responsible for defending against infection and disease, including returning tissue fluid to the bloodstream?

• A. Immune system
• B. Endocrine system
• C. Digestive system
• D. Lymphatic system

Answer: (D)

The lymphatic system handles both defending against infection and returning tissue fluid to the bloodstream. It collects the small amount of fluid that leaks from capillaries as interstitial fluid, forming lymph that travels through lymphatic vessels. Along the way, lymph nodes and other lymphoid tissues host immune cells that monitor for pathogens and mount responses, providing immune defense. Finally, lymph is returned to the bloodstream via the thoracic duct and right lymphatic duct, completing the circulation loop. The immune system also protects against disease, but its defense work relies on the network of vessels and nodes of the lymphatic system to transport immune cells and to filter lymph. The digestive and endocrine systems don’t have this combined role of fluid return and immune surveillance, so they’re not the best fit for this description.

The lymphatic system handles both defending against infection and returning tissue fluid to the bloodstream. It collects the small amount of fluid that leaks from capillaries as interstitial fluid, forming lymph that travels through lymphatic vessels. Along the way, lymph nodes and other lymphoid tissues host immune cells that monitor for pathogens and mount responses, providing immune defense. Finally, lymph is returned to the bloodstream via the thoracic duct and right lymphatic duct, completing the circulation loop.

The immune system also protects against disease, but its defense work relies on the network of vessels and nodes of the lymphatic system to transport immune cells and to filter lymph. The digestive and endocrine systems don’t have this combined role of fluid return and immune surveillance, so they’re not the best fit for this description.