Question

What are mainly reabsorbed from Henle's loops? (a) Potassium (b) Glucose (c) Water and \(\mathrm{NaCl}\) (d) Urea and \(\mathrm{NaCl}\)

Short answer

The substances primarily reabsorbed from Henle's loops are Water and \(\mathrm{NaCl}\).

Step-by-step solution

Understand the Function of Henle's loop

Henle's loop, also called the loop of Henle, is part of a nephron in the kidney. It plays a vital role in kidneys' task of regulating the concentration of water and saline in the body. It does this by reabsorbing these elements from the urine before it's excreted.

Identify the Substances Mostly Reabsorbed

The substances which are chiefly and systematically reabsorbed from the Henle's loop are water and sodium chloride, denoted scientifically as \(\mathrm{NaCl}\). Other materials may also get reabsorbed in various parts of the nephron, but water and \(\mathrm{NaCl}\) are the most evident in the Henle's loop.

Match Identified Substances with the Choices Given

Now, matching the identified substances primarily reabsorbed from the Henle's loop to the options given, it is clear that the correct answer is (c) Water and \(\mathrm{NaCl}\).

Key concepts

Nephron Structure

The nephron is the functional unit of the kidney, each one specially crafted to filter blood and produce urine. It consists of a renal corpuscle and a renal tubule. The renal corpuscle is the initial filtering component and includes the glomerulus, where blood is initially filtered, and Bowman's capsule, which encases the glomerulus. From here, the filtrate – a mix of water, ions, glucose, and waste – travels into the renal tubule.

The renal tubule is a winding, tube-like structure divided into several segments: the proximal convoluted tubule, leading to the loop of Henle (or Henle's loop), followed by the distal convoluted tubule, and then the connecting tubule. Henle's loop is an essential part of this structure, dipping into the kidney's medulla and returning. It is responsible for creating a high concentration of salts in the surrounding tissue which is crucial for urine concentration regulation, a topic we'll delve into later in this article.

The Importance of Nephron Complexity

Understanding the intricacies of each nephron segment allows us to appreciate the meticulous process of urine formation and the kidney's ability to maintain homeostasis. The loop of Henle, in particular, showcases this complexity as it creates a concentration gradient that aids in water reabsorption.

Kidney Reabsorption Process

Reabsorption in the kidney is a critical mechanism for retaining vital substances that the body needs while eliminating waste. As filtrate moves through the nephron, different segments reabsorb various components into the bloodstream. In the proximal convoluted tubule, for instance, most of the glucose, amino acids, and a significant proportion of ions and water are reabsorbed.

When filtrate enters Henle's loop, the kidney's reabsorption strategy intensifies. The loop's descending limb is permeable to water but not to salts, meaning as it flows down, the filtrate becomes increasingly concentrated as water exits via osmosis into the salty medullary space. Conversely, the ascending limb is impermeable to water but actively pumps out NaCl, which dilutes the filtrate as it moves towards the distal tubule.

Active and Passive Reabsorption

Differentiating between active and passive reabsorption is crucial. Active reabsorption requires energy, like the NaCl transport in the loop's ascending limb. But down the descending limb, water reabsorbs passively, driven by osmotic gradients without expending cellular energy.

Urine Concentration Regulation

The regulation of urine concentration is a model of physiological finesse, and it occurs primarily via Henle's loop. This loop, utilizing the countercurrent multiplier system, sets up an osmotic gradient in the kidney's medulla that is essential for water reabsorption from the filtrate.

As the filtrate descends in the loop, it encounters an increasingly salty environment, which draws water out, leaving the filtrate concentrated. Ascending, NaCl is actively removed, reducing the filtrate's salt content but keeping the medulla salty for the descending limb. This countercurrent mechanism magnifies the concentration gradient, enabling precise control over water reabsorption.

ADH and Aldosterone: Hormonal Control

Key hormones including antidiuretic hormone (ADH) and aldosterone tightly regulate this process. ADH increases the permeability of the distal tubules and collecting ducts to water, enhancing reabsorption and producing concentrated urine. Aldosterone prompts NaCl reabsorption, which indirectly increases water reabsorption through osmotic balance. The fine-tuned interplay of these mechanisms allows the kidneys to conserve water efficiently and manage the body’s fluid and electrolyte balance.