Reabsorption of Filtrate in the Nephrons

In the kidneys, the functional units responsible for filtering blood and producing urine are called nephrons. Each kidney contains millions of nephrons, which play a crucial role in maintaining the body's fluid balance and removing waste products.

Filtration Process in the Nephrons

The process of filtration begins in the glomerulus, a network of capillaries located within the nephron. Here, blood pressure forces water, ions, and small molecules to pass through the walls of the capillaries and enter the renal tubules. This filtrate contains waste products, such as urea, as well as essential substances like glucose and electrolytes.

Reabsorption of Filtrate

The filtrate then moves through the renal tubules, where a significant amount of reabsorption occurs. Reabsorption refers to the process by which substances from the filtrate are transported back into the bloodstream.

Importance of Reabsorption

Reabsorption is crucial for maintaining homeostasis and conserving valuable substances within the body. It ensures that essential nutrients, such as glucose and amino acids, are returned to the bloodstream instead of being excreted in the urine. Additionally, reabsorption helps regulate the body's water balance by selectively reabsorbing water from the filtrate.

Reabsorption Mechanisms

Reabsorption in the nephrons occurs through different mechanisms, including passive diffusion, active transport, and facilitated diffusion. These mechanisms allow for the selective reabsorption of specific substances based on their concentration gradients and the needs of the body.

Reabsorption Sites

Different segments of the renal tubules are responsible for reabsorbing specific substances. For example, the proximal convoluted tubule (PCT) reabsorbs the majority of filtered water and essential solutes like glucose and amino acids. The loop of Henle is involved in reabsorbing water and electrolytes, while the distal convoluted tubule (DCT) regulates the reabsorption of ions, such as sodium and potassium.

Amount of Filtrate Excreted as Urine

While a large quantity of fluid is filtered by the nephrons each day, only a small percentage is excreted as urine. This is because the majority of the filtrate is reabsorbed back into the bloodstream. The reabsorbed substances are transported through the peritubular capillaries surrounding the renal tubules and eventually return to the general circulation.

Conclusion

In summary, the correct answer is option 'B' - the remaining 99% of the filtrate is reabsorbed into the blood. Reabsorption is a fundamental process in the nephrons, allowing for the conservation of essential substances and the regulation of water balance. Without reabsorption, the body would lose valuable nutrients and struggle to maintain proper fluid levels.