Creatinine the waste product closely regulated by the brain and kidneys is the end product of the metabolism of HomeExcretory System MCQsCreatinine the waste product closely regulated by the brain and kidneys is the end product of the metabolism of Q. Creatinine the waste product closely regulated by the brain and kidneys is the end product of the metabolism of A. Ammonia B. Muscle C. Nucleotide D. Anaerobic Answer: Muscle