What bodily fluid is primarily filtered by the kidneys?

The primary bodily fluid filtered by the kidneys is blood. The kidneys play a crucial role in maintaining homeostasis by regulating the composition of blood. They filter waste products, excess substances, and fluids from the bloodstream to form urine, which is then excreted from the body. During this filtration process, the kidneys remove toxins, metabolic waste, and excess ions, while also reabsorbing essential nutrients and water back into the bloodstream. This function is vital for regulating blood pressure, electrolyte balance, and overall fluid balance in the body.

While urine is the end product of the filtration process, it is not the fluid that is directly filtered; rather, it is the result of blood filtration. Saliva and lymph do not play a role in the kidney's filtration function.