Each human kidney contains microscopic filtering units called nephrons. Approximately how many nephrons are present in a single normal human kidney?

Introduction / Context:
The nephron is the basic structural and functional unit of the kidney, responsible for filtration of blood and formation of urine. The total number of nephrons in each kidney gives a sense of how much filtering capacity the organ has. This question tests your ability to recall the approximate number of nephrons present in a single normal human kidney.

Given Data / Assumptions:

• The focus is on a single human kidney, not both combined.
• We are asked for an approximate count, not an exact number for every individual.
• Options range from thousands to millions of nephrons.
• We assume a healthy adult kidney without disease or developmental issues.

Concept / Approach:
An adult human typically has around one million nephrons in each kidney, giving a total of about two million for both kidneys combined. Although the exact number varies between individuals, this order of magnitude is standard in textbooks. Values such as 10,000 or 100,000 per kidney are too low and would not provide enough filtering surface. Values like 10 million per kidney are higher than commonly reported. Therefore, the best approximate answer is 1,000,000 nephrons per kidney.

Step-by-Step Solution:
Step 1: Recall that each kidney contains many microscopic nephrons responsible for filtration and reabsorption. Step 2: Remember the typical textbook figure of around one million nephrons per kidney. Step 3: Compare this to the provided options, noting that 1,000,000 matches the known value. Step 4: Recognise that 10,000 and 1,000 are far too low for adequate kidney function in humans. Step 5: Note that 100,000 is still below the commonly accepted range and would understate nephron number. Step 6: See that 10,000,000 is above typical estimates and not usually mentioned in basic biology sources. Step 7: Conclude that the most appropriate approximate value is 1,000,000 nephrons per kidney.

Verification / Alternative check:
Human anatomy and physiology textbooks generally state that each human kidney contains about one million nephrons, sometimes giving a range such as eight hundred thousand to one point two million. This range centres around 1,000,000, which matches the option. Clinical discussions of chronic kidney disease also mention that nephron loss over time reduces kidney function, reinforcing that there is a large starting number of nephrons per kidney.

Why Other Options Are Wrong:
100,000: Too low compared with standard estimates of nephron number per kidney. 10,000: Far lower than established values, insufficient for normal human kidney function. 1,000: Extremely low and incompatible with known renal anatomy. 10,000,000: Much higher than typical textbook values and not supported by standard references.

Common Pitfalls:
Students sometimes confuse the number of nephrons in one kidney with the total in both kidneys or misremember the order of magnitude. A simple way to remember is one million per kidney, two million in total for a healthy adult. Keeping this approximate figure in mind helps answer related exam questions quickly.

Final Answer:
Each normal human kidney contains approximately 1,000,000 nephrons.