Question

Select the total number of correct statements about the loop of Henle. (1) Descending limb is permeable to water. (2) Descending limb is almost impermeable to electrolyte. (3) Ascending limb is impermeable to water. (4) It allows the transport of electrolyte only actively. (5) At the tip of loop of Henle, the concentration of filtrate is \(1200 \mathrm{~m} \operatorname{osmol} / 1\). (6) It helps in the maintenance of high osmolarity in medullary interstitium. (a) 6 (b) 3 (c) 4 (d) 5

Short answer

The total number of correct statements about the loop of Henle is 5. So, the correct answer would be equivalent to an option that gives the number '5', if one exists amongst the provided choices.

Step-by-step solution

Evaluate each statement

Here's a breakdown of each statement, considering what is known about the Loop of Henle: \n(1) True - The descending limb is indeed permeable to water.\n(2) True - This limb is also impermeable to electrolytes like salt. \n(3) True - The ascending limb of the loop of Henle is impermeable to water. \n (4) False - The ascending limb allows passive and active transport of electrolytes.\n (5) True - At the bend or tip of the loop of Henle, the filtrate can reach a high concentration due to the removal of water.\n (6) True - The Loop of Henle plays a critical role in maintaining a high osmolarity in the medullary interstitium, which helps in the concentration of urine.

Count the number of correct statements

From the analysis in step 1, there are five correct statements: 1, 2, 3, 5 and 6.

Key concepts

Descending limb permeability

The descending limb of the Loop of Henle has a unique characteristic: it is highly permeable to water. This means water can easily pass through its walls from the filtrate inside the nephron into the surrounding tissue. This process is crucial for water reabsorption.
As water exits, the filtrate becomes increasingly concentrated because electrolytes like salts are largely left behind. By reabsorbing water in this manner, the kidney can regulate water balance in the body efficiently.
This permeability is essential for forming urine that is more concentrated than blood, allowing the body to conserve water when needed.

• High water permeability
• Water moves out, increasing filtrate concentration
• Crucial for water conservation

Ascending limb water impermeability

The ascending limb of the Loop of Henle exhibits a different characteristic compared to the descending limb: it is impermeable to water. This impermeability means that water cannot exit or enter this part of the nephron.
Instead, the ascending limb focuses on reabsorbing electrolytes, such as sodium and chloride, from the filtrate. This is largely through active transport methods, burning energy in the process.
By doing so, it helps dilute the filtrate as it ascends, preparing it for further processing in the distal parts of the nephron.

• Water cannot pass through
• Focuses on electrolyte reabsorption
• Helps dilute the filtrate

Electrolyte transport

Within the Loop of Henle, the transportation of electrolytes is crucial for the kidney's function in controlling salt balance and blood pressure.
The descending limb is almost impermeable to electrolytes, allowing them to remain within the filtrate as water exits.
Conversely, the ascending limb actively and passively transports electrolytes out of the filtrate and into the surrounding interstitial fluid. Active transport requires energy to move electrolytes against their concentration gradient, whereas passive transport allows their movement along the gradient without energy use.

• Descending limb: electrolytes retained
• Ascending limb: active and passive transport
• Critical for salt balance

Filtrate concentration

As the filtrate travels through the Loop of Henle, its concentration changes significantly. At the tip, it is highly concentrated due to the reabsorption of water in the descending limb.
This high concentration at the tip, sometimes up to about 1200 mOsm/L (milliosmoles per liter), is essential for urine concentration. It acts as a foundational step in the kidney's ability to reabsorb water and form urine that is concentrated or dilute, based on the body's needs.
The concentration gradient created by this process is key in kidney function.

• Concentration increases in descending limb
• High concentration at the tip
• Essential for urine concentration

Osmolarity in medullary interstitium

The Loop of Henle plays an essential role in establishing and maintaining high osmolarity in the medullary interstitium of the kidney.
This high osmolarity is crucial as it creates the osmotic gradient necessary for water reabsorption in the collecting ducts. It ensures the kidney can produce urine that is more concentrated than blood. Thanks to the unique properties of both limbs of the loop and the transport processes, this osmolarity is maintained effectively, helping regulate the body's hydration status.

• Maintains high osmolarity in medulla
• Creates osmotic gradient for water reabsorption
• Vital for urine concentration control