Approximately how many nephrons are in each kidney?

• A. One thousand
• B. One million
• C. Ten thousand
• D. Hundred thousand

Answer: (A)

Nephrons are the kidney’s filtering workhorses, each one filtering blood, reabsorbing what the body needs, and forming urine. In an adult, each kidney contains about one million nephrons, and together they provide the large filtration surface and processing capacity the kidneys rely on to maintain fluid and electrolyte balance. That means roughly two million nephrons in total across both kidneys. Numbers in the thousands or tens of thousands would imply far less filtration power and an imperfect ability to form urine. So the approximate count per kidney is around one million.