Understanding Henle's Loop Function

Henle's loop is a critical part of the nephron in the kidney, involved in creating concentrated urine. Its primary function is to establish a concentration gradient in the renal medulla, which allows for water reabsorption later in the process.

Step 1: Understand the Structure

Henle's loop has two main parts:

• Descending Limb: This part is permeable to water but not to salts.
• Ascending Limb: This part is impermeable to water but actively transports salts out into the surrounding tissue.

Step 2: The Process of Creating a Gradient

The ascending limb actively pumps out sodium (Na⁺) and chloride (Cl^-) ions. This can be represented by the active transport equation for the Na⁺/K⁺ ATPase pump:

$3{\mathrm{Na}}^{+}\left(\mathrm{in}\right)+2K^{+}\left(\mathrm{out}\right)+\mathrm{ATP}\to 3{\mathrm{Na}}^{+}\left(\mathrm{out}\right)+2K^{+}\left(\mathrm{in}\right)+\mathrm{ADP}+P_i$

This action makes the tissue around the loop (the interstitium) salty, creating a high osmotic gradient.

Step 3: Water Reabsorption

As the filtrate moves down the descending limb, water passively moves out into the salty interstitium due to osmosis. This concentrates the filtrate inside the loop.

Step 4: Final Outcome

The combined action of salt removal in the ascending limb and water removal in the descending limb results in the reabsorption of both water and salt. This process is essential for conserving water in the body and producing urine that is more concentrated than blood plasma.

Final Answer

Based on this detailed process, the correct function of Henle's loop is: Reabsorption of water & salt both.

Related Topics & Formulae

Counter-Current Multiplier System

Henle's loop acts as a counter-current multiplier. The flow of filtrate in opposite directions in the two limbs multiplies the salt concentration gradient, making it much stronger than it could be with a single pass. This is the key mechanism for building the osmotic gradient.

Osmosis

The movement of water out of the descending limb is driven by osmosis. The osmotic pressure (Π) can be calculated using the van't Hoff equation:

$\Pi =iCRT$

Where: $\Pi$ is osmotic pressure, $i$ is the van't Hoff factor, $C$ is the molar concentration, $R$ is the gas constant, and $T$ is temperature. A higher salt concentration (C) in the interstitium creates a higher osmotic pressure, pulling more water out.

Active Transport

The energy-dependent pumping of ions against their concentration gradient is called active transport. This process requires ATP hydrolysis, as shown in the equation above.