Which structure in the human body acts as a countercurrent exchanger to maintain homeostasis?

• A. Loop of Henle
• B. Thyroid gland
• C. Alveoli
• D. Sinoatrial node

Answer: (A)

Verified step by step guidance

1. Understand the concept of countercurrent exchange: This is a mechanism that allows for efficient transfer of substances (such as heat or solutes) between two fluids flowing in opposite directions. It is crucial for maintaining homeostasis in various physiological systems.
2. Identify the role of the Loop of Henle: The Loop of Henle is a structure in the nephron of the kidney that plays a key role in concentrating urine and conserving water. It uses a countercurrent multiplier system to create a concentration gradient in the medulla of the kidney.
3. Explore the anatomy of the Loop of Henle: The Loop of Henle consists of a descending limb and an ascending limb. The descending limb is permeable to water but not to solutes, while the ascending limb is permeable to solutes but not to water.
4. Examine how the Loop of Henle functions as a countercurrent exchanger: As fluid flows down the descending limb, water is reabsorbed into the surrounding tissue, concentrating the solutes. As fluid ascends the ascending limb, solutes are reabsorbed, further concentrating the urine.
5. Conclude why the Loop of Henle is the correct answer: The Loop of Henle's countercurrent mechanism is essential for the kidney's ability to concentrate urine and maintain water and electrolyte balance, which is a critical aspect of homeostasis.