Question

Diuretic drugs that act in the nephron loop a. inhibit active sodium transport. b. cause an increased flow of filtrate to the distal convoluted tubule. c. cause an increased secretion of potassium into the tubule. d. promote the excretion of salt and water. e. do all of these.

Short answer

All the given statements (a, b, c, and d) correctly describe the actions of diuretic drugs that act in the nephron loop, so the answer is e: do all of these. These drugs inhibit active sodium transport, cause an increased flow of filtrate to the distal convoluted tubule, cause an increased secretion of potassium into the tubule, and promote the excretion of salt and water.

Step-by-step solution

Statement a: Inhibit active sodium transport

Diuretic drugs that act in the nephron loop do inhibit the active transport of sodium. They specifically block the sodium-potassium-chloride (Na-K-2Cl) co-transporter in the thick ascending limb of the nephron loop. By doing so, they prevent the reabsorption of sodium, potassium, and chloride ions, leading to increased diuresis (increased urine production)

Statement b: Cause an increased flow of filtrate to the distal convoluted tubule

By inhibiting the reabsorption of sodium, potassium, and chloride ions in the nephron loop, diuretic drugs cause more filtrate to flow into the distal convoluted tubule. This increased flow of filtrate leads to an increased volume of urine being produced, which is the primary goal of diuretic therapy.

Statement c: Cause an increased secretion of potassium into the tubule

As diuretics inhibit the Na-K-2Cl co-transporter in the thick ascending limb of the nephron loop, they indirectly cause an increased secretion of potassium into the tubule. This happens because more sodium reaches the distal convoluted tubule and collecting duct, leading to an exchange of sodium ions for potassium ions, which get secreted into the tubule. This effect can contribute to hypokalemia (low potassium levels) in patients who use these types of diuretics.

Statement d: Promote the excretion of salt and water

Diuretics that act in the nephron loop promote the excretion of salt and water by inhibiting the reabsorption of sodium, potassium, and chloride ions. As these ions are not reabsorbed, more water remains in the tubule, ultimately resulting in an increased excretion of salt and water in the form of urine.

Conclusion

Based on our analysis, all of the given statements (a, b, c, and d) are correct in describing the actions of diuretic drugs that act in the nephron loop. Therefore, the answer is e: do all of these.

Key concepts

Nephron Loop

The nephron loop, commonly known as the Loop of Henle, plays a crucial role in urine formation and concentration within the kidneys. This loop is nestled between two other parts of the nephron: the proximal convoluted tubule and the distal convoluted tubule. Its primary function is to create a concentration gradient in the medulla of the kidney. This gradient is essential for the reabsorption and conservation of water and ions.

The nephron loop consists of two limbs: the descending limb, which is permeable to water, and the ascending limb, which is impermeable to water but actively transports ions. It's in the thick ascending limb that important transport mechanisms, like the sodium-potassium-chloride co-transporter, come into play to fine-tune the body's balance of water and salts.

Sodium-Potassium-Chloride Co-Transporter

The sodium-potassium-chloride co-transporter (abbreviated as Na-K-2Cl) is a key protein channel located in the thick ascending limb of the nephron loop. This transporter actively reabsorbs sodium, potassium, and chloride ions from the tubule back into the bloodstream. By doing so, it helps in concentrating urine and maintaining the body's electrolyte balance.

When loop diuretics are introduced, they block this transporter, preventing the reabsorption of these ions. As a result, more ions remain in the tubular fluid, leading to increased fluid retention in the loop. This ultimately results in higher urine production and the excretion of excess salts from the body. Such actions make loop diuretics effective in conditions that require the reduction of fluid overload.

Hypokalemia

Hypokalemia refers to an abnormally low level of potassium in the blood, which can arise as a side effect of using loop diuretics. When the Na-K-2Cl co-transporter is inhibited in the nephron loop, more sodium reaches the distal parts of the nephron. Here, sodium is reabsorbed in exchange for potassium and hydrogen ions, leading to the increased secretion and excretion of potassium.

This can result in hypokalemia, potentially causing various symptoms such as muscle weakness, cramps, fatigue, and even heart arrhythmias. It's important for patients using loop diuretics to monitor their potassium levels and possibly use potassium supplements or adjust their diet to prevent this condition.

Urine Production

Urine production is a vital process to rid the body of excess fluids and wastes. It begins in the nephron, where blood filtration occurs. The nephron loop, especially the thick ascending limb, plays a pivotal role in the concentration of urine. Through active transport mechanisms like the Na-K-2Cl co-transporter, specific ions are reabsorbed, while water remains, increasing urine volume.

Diuretics enhance urine production by inhibiting ion reabsorption. By blocking transporters, they increase water and solute excretion, effectively promoting urine output. This mechanism is particularly useful in treating conditions where reducing fluid buildup is essential, such as hypertension, heart failure, or certain kidney disorders.