Question

Some types of mammals have especially long loops of Henle that maintain a steep osmotic gradient. This adaptation enables the organism to A. excrete urine of higher osmolarity. B. secrete less solute across the membrane into the renal tubule. C. produce urine that is isotonic to body fluids. D. reabsorb more blood proteins such as albumin.

Short answer

A. excrete urine of higher osmolarity.

Step-by-step solution

Understanding the Function of the Loop of Henle

The Loop of Henle is a part of the nephron in the kidney and plays a crucial role in the concentration of urine. It helps establish a gradient of osmolarity in the renal medulla.

Importance of Osmotic Gradient

A steep osmotic gradient allows for the reabsorption of more water from the filtrate as it passes through the collecting ducts, leading to the production of urine with varying concentrations.

Adaptation of Long Loops of Henle in Some Mammals

Mammals with long loops of Henle can create a stronger osmotic gradient, which enables them to produce urine that is highly concentrated in comparison to their body fluids.

Evaluating the Choices

A. Excrete urine of higher osmolarity - correct answer, as long loops of Henle enable production of highly concentrated urine. B. Secrete less solute across the membrane - incorrect, this is not directly related to the function of the Loop of Henle. C. Produce urine that is isotonic to body fluids - incorrect, the function is to create urine that can be more concentrated. D. Reabsorb more blood proteins - incorrect, protein reabsorption primarily occurs in the proximal tubule.

Key concepts

osmotic gradient

The osmotic gradient is crucial for the kidney's ability to concentrate urine. It is created in the renal medulla by the Loop of Henle. As the filtrate moves down the descending limb, water is reabsorbed into the surrounding medullary tissue due to the high osmolarity outside the tubule. This results in a more concentrated filtrate. In contrast, the ascending limb is impermeable to water and actively transports ions out of the tubule into the interstitial fluid. This process makes the filtrate less concentrated.
The key to this gradient is maintaining a high solute concentration in the medulla, which allows the kidney to reabsorb water from the collecting ducts, making the final urine concentrated and conserving water in the body.

urine concentration

Urine concentration is largely determined by the action of the Loop of Henle. When mammals, like those with long loops of Henle, have a steep osmotic gradient, they can produce urine with high osmolality, meaning it has a high concentration of solutes compared to body fluids. This process is essential for water conservation, especially in environments where water is scarce. It involves the reabsorption of water due to the gradient, leaving behind a concentrated solute residue.
This ability is particularly advantageous for desert animals, allowing them to survive with minimal water intake while still effectively excreting waste products.

kidney nephron

The nephron is the functional unit of the kidney, and it includes several key structures: Bowman's capsule, proximal tubule, Loop of Henle, distal tubule, and collecting duct. Each part of the nephron has a specific role in filtering blood, reabsorbing water and necessary solutes, and excreting waste. The Loop of Henle, a pivotal section found within the medulla, is responsible for creating the osmotic gradient mentioned above.
This structure's functionality is essential for the kidney's ability to concentrate urine. When blood enters the nephron, filtration occurs in the glomerulus, and the resultant filtrate passes sequentially through nephron segments, where precise reabsorption and secretion processes fine-tune the composition of the final urine. A key feature is that each nephron operates similarly to handle small volumes of filtrate concurrently, efficiently managing the body's fluid and electrolyte balance.