As a result of filtration along with excretory products certain useful products like glucose, salt etc are also filtered but these are not excreted. Explain. A

As a result of filtration, certain useful products like glucose and salt are also filtered along with excretory products. However, these useful products are not excreted because they are reabsorbed by the body.

Here is a step-by-step explanation:

1. Filtration: Filtration is the first step in the process of urine formation. It occurs in the glomerulus of the kidney, where blood is filtered to form a fluid called glomerular filtrate. This filtrate contains waste products, such as urea and creatinine, as well as useful substances like glucose and salt.

2. Reabsorption: After filtration, the glomerular filtrate passes through the renal tubules, where reabsorption takes place. Reabsorption is the process by which useful substances are transported back into the bloodstream. In the case of glucose and salt, they are reabsorbed by active transport mechanisms in the renal tubules.

3. Glucose reabsorption: Glucose is an essential energy source for the body. In a healthy individual, almost all of the filtered glucose is reabsorbed in the proximal tubules of the nephron. This is achieved through the action of glucose transporters, which actively transport glucose from the tubular fluid back into the bloodstream.

4. Salt reabsorption: Salt, or sodium chloride, is important for maintaining fluid balance and blood pressure. It is reabsorbed in various segments of the renal tubules, primarily in the proximal tubules and the loop of Henle. Sodium transporters actively transport sodium ions out of the tubular fluid and into the bloodstream, leading to the reabsorption of salt.

5. Excretion of waste products: While useful substances like glucose and salt are being reabsorbed, waste products such as urea and creatinine continue to be excreted in the urine. These waste products are not reabsorbed because they are not needed by the body and need to be eliminated.

In summary, filtration in the kidneys allows for the removal of waste products and the filtration of useful substances like glucose and salt. However, through the process of reabsorption, the body is able to retain and reabsorb these useful substances back into the bloodstream, ensuring that they are not excreted.