How does lead exit the body once it is in the bloodstream?

Lead is a heavy metal that can accumulate in the body, particularly affecting organs such as the kidneys and brain. Once lead enters the bloodstream, the primary routes for its excretion include urination, sweat, and exhaling.

The kidneys filter the blood and help to eliminate lead through urine, which is one of the most significant pathways for removing this toxic metal from the body. Additionally, some lead can be excreted through sweat and, to a lesser extent, through respiratory exhalation, as the body attempts to rid itself of toxins.

Digestion is not a viable pathway for exiting lead that is already in the bloodstream; instead, it is more relevant to how lead may enter the body through contaminated food or materials. Skin absorption is also not a mechanism for lead to exit the body; while it can enter through the skin, this does not relate to the elimination process. Hair loss may occur due to toxic exposure, but it does not function as an effective means of lead elimination from the body.

Thus, the correct choice highlights the essential ways the human body processes and eliminates lead that has entered the bloodstream.