Which organ is primarily responsible for filtering blood in the human body?

The organ primarily responsible for filtering blood in the human body is the kidney. Each kidney contains millions of tiny structures called nephrons that play a critical role in this process. Nephrons filter out waste products and excess substances from the blood, which are then excreted as urine. This filtration is essential for maintaining the body's overall fluid and electrolyte balance, as well as regulating blood pressure and ensuring that harmful toxins are removed from the bloodstream.

The other options serve different functions: the liver processes nutrients and detoxifies substances; the heart pumps blood throughout the body; and the lungs are involved in gas exchange, bringing oxygen into the bloodstream and removing carbon dioxide. Each organ has a distinct and vital function, but it is the kidney that specializes in the filtration of blood.