What system is responsible for returning fluid to the bloodstream?

The lymphatic system is key to returning fluid to the bloodstream. It collects excess interstitial fluid that accumulates in tissues and returns it to the circulatory system, maintaining fluid balance within the body. This system also plays a crucial role in immune function, as it transports lymph, which contains white blood cells that help the body fight infections.

When interstitial fluid is not drained, it can lead to swelling or edema. The lymphatic vessels carry this fluid back toward the heart, where it reenters circulation, often at the junction of the subclavian and internal jugular veins.

In contrast, while the circulatory system is also involved in transporting fluids, its primary role is to circulate blood and deliver nutrients and oxygen to tissues, rather than specifically managing interstitial fluid levels. The digestive system is primarily concerned with nutrient absorption and waste elimination, and the respiratory system is involved in gas exchange, not the management of bodily fluids.