Examining the function of lymph, what happens to lymph as it circulates?

As lymph circulates through the lymphatic system, it performs the essential function of cleaning and filtering the fluid that has escaped from the blood vessels into the body's tissues. This process occurs as lymph passes through lymph nodes, where it is exposed to immune cells that identify and destroy pathogens, such as bacteria and viruses.

Consequently, the lymph, which begins as a clear fluid similar to plasma but contains waste products, pathogens, and excess interstitial fluid, is purified and cleansed as it travels. By the time it reaches the bloodstream, the lymph is significantly cleaner and contributes to maintaining the body’s immune defense and overall fluid balance. This transformation is vital for the body’s health, ensuring that harmful substances are removed while essential nutrients are retained.

In contrast, the other options suggest changes to lymph that do not reflect its actual physiological process. For instance, lymph does not convert into plasma or become murky; rather, it becomes cleaner as it circulates. It also does not thicken or get expelled; instead, it is absorbed into the circulatory system in a purified state.