The initial filtrate entering the nephron from the blood is also called what?

• A. Urine
• B. Primary urine
• C. Filtrate (glomerular filtrate)
• D. Blood plasma

Answer: (C)

The fluid that first enters the nephron from the blood is the glomerular filtrate, often just called the filtrate. This happens when plasma is filtered across the glomerular membrane into Bowman's capsule, so the nephron starts with the filtrate as its input. It’s sometimes called primary urine because it’s the initial fluid before the tubules reabsorb or secrete substances. It’s not urine yet, since urine is the final waste fluid after tubular processing, and it’s not blood plasma because plasma remains in the blood and is separated from the filtrate by the filtration barrier. In a healthy kidney, the filtrate contains water, electrolytes, glucose, amino acids, and other small solutes, with large proteins and cells kept out.