Question

Read the given statements and select the correct option. Statement 1 : In the descending limb of loop of Henle, the urine is hypertonic, while in the ascending limb of loop of Henle, the urine becomes hypotonic. Statement \(2:\) Descending limb is impermeable to \(\mathrm{Na}^{+}\), while ascending limb is impermeable to \(\mathrm{H}_{2} \mathrm{O}\). (a) Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement 1 . (b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement \(1 .\) (c) Statement 1 is correct and statement 2 is incorrect. (d) Both statements 1 and 2 are incorrect.

Short answer

Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement 1, making option (a) the correct choice.

Step-by-step solution

Understanding Statement 1

In the descending limb of loop of Henle, the filtrate becomes increasingly hypertonic as it moves down because it is permeable to water but not to solutes. Therefore, water leaves the filtrate, increasing the concentration of solutes. In the ascending limb of loop of Henle, the filtrate becomes hypotonic because this segment is impermeable to water and actively transports solutes out of the filtrate, decreasing its solute concentration.

Understanding Statement 2

The descending limb of the loop of Henle is indeed impermeable to \(\mathrm{Na}^{+}\) and other solutes; it allows for water reabsorption into the surrounding interstitial fluid. Conversely, the ascending limb is impermeable to \(\mathrm{H}_{2}O\) and actively transports \(\mathrm{Na}^{+}\) and other solutes out of the tubular fluid.

Evaluating the Truth of the Statements

Since statement 1 accurately describes the tonicity changes in the descending and ascending limbs, and statement 2 correctly identifies the permeability characteristics of each limb, both statements 1 and 2 are correct.

Determining the Relationship Between Statement 1 and Statement 2

Statement 2 provides an explanation for why the filtrate becomes hypertonic in the descending limb (permeable to water) and hypotonic in the ascending limb (permeable to solutes and actively transporting them out), which directly relates to the conditions described in statement 1. Therefore, statement 2 is the correct explanation of statement 1.

Key concepts

Renal Physiology

Renal physiology is a branch of the physiological sciences that focuses on the structure and function of the kidneys. At the forefront of this field is the sophisticated process by which kidneys filter blood, remove waste, and regulate the body's fluid balance. This takes place through a series of steps involving the glomerulus, renal tubules, and various segments such as the loop of Henle, which plays a critical role in urine concentration.

The loop of Henle, specifically, is essential for the kidney's ability to produce urine with varying concentrations. This structure is composed of two limbs – the descending and ascending limbs, each with distinct permeability properties that significantly influence the urine's tonicity or solute concentration. Understanding these differences is crucial in deciphering how kidneys maintain homeostasis within the body.

In terms of educational content, students might benefit from visual aids, such as diagrams illustrating the nephron structure, including the loop of Henle. Also, integrating interactive simulations where learners can manipulate the permeability and observe the consequent changes in urine concentration could reinforce comprehension.

Urine Concentration

Urine concentration is a term that refers to the amount of solutes present in the urine, a process that the kidneys meticulously regulate. The kidneys are capable of generating urine that is either more concentrated or more diluted than blood plasma, depending on the body's needs. This adjustment is largely made in the loop of Henle.

The descending limb of the loop is permeable to water but not to solutes like sodium ions (a+) which leads to water being reabsorbed into the bloodstream, thereby increasing the filtrate's solute concentration or tonicity. Conversely, the ascending limb is impermeable to water but actively transports sodium ions out, resulting in a decrease in the filtrate's solute concentration, making it hypotonic.

For teaching purposes, a focus on visualizing and understanding osmosis and active transport can aid students. Providing detailed steps of how the solute composition changes as the filtrate moves through the loop of Henle can clarify this complex concept.

Osmoregulation

Osmoregulation is the biological process by which organisms maintain the balance of water and minerals in their bodies. In the context of renal physiology, the kidneys play a pivotal role in this homeostatic mechanism by controlling the volume and concentration of urine. The loop of Henle, through its differential permeability along its descending and ascending limbs, executes a countercurrent multiplier mechanism that is fundamental for osmoregulation.

The descending limb allows water to exit the filtrate, increasing its osmolality, while the ascending limb’s active transport of solutes without allowing water movement results in a reduced osmotic pressure. Therefore, the loop of Henle establishes a gradient that enables the kidney to vary urine concentration as needed. In extreme dehydration, this system works to conserve water, producing highly concentrated urine. Conversely, in a state of overhydration, the kidney can excrete dilute urine to reduce bodily fluids.

For students grappling with these concepts, emphasizing the relationship between the loop of Henle's function and the body's water balance, alongside the concept of countercurrent exchange, could greatly enhance understanding. Real-world examples, such as the kidney's response to dehydration, can provide tangible context to these abstract ideas.