Cells lining kidney tubules function in the reabsorption of water from urine. In response to chemical signals, they reversibly insert additional aquaporins into their plasma membranes. In which of these situations would your tubule cells have the most aquaporins: after a long run on a hot day, right after a large meal, or after drinking a large bottle of water? Explain.

Verified step by step guidance

1. Understand the role of aquaporins: Aquaporins are membrane proteins that facilitate water transport across cell membranes. They are crucial for water reabsorption in kidney tubules.
2. Consider the body's need for water reabsorption: After a long run on a hot day, the body loses a significant amount of water through sweat, increasing the need for water reabsorption to maintain homeostasis.
3. Analyze the situation after a large meal: While digestion requires some water, it does not typically lead to a significant immediate need for increased water reabsorption in the kidneys.
4. Evaluate the scenario after drinking a large bottle of water: In this case, the body has an excess of water, reducing the need for reabsorption, and thus fewer aquaporins would be inserted.
5. Conclude which situation requires the most aquaporins: The situation that demands the most water reabsorption, and therefore the most aquaporins, is after a long run on a hot day.

Key Concepts

Aquaporins

Aquaporins are specialized water channel proteins embedded in cell membranes that facilitate the rapid transport of water molecules. In kidney tubule cells, the presence of aquaporins is crucial for the reabsorption of water from urine, allowing the body to maintain fluid balance and prevent dehydration.

Hormonal Regulation

Hormonal regulation plays a significant role in the insertion of aquaporins into the plasma membranes of kidney tubule cells. Hormones such as antidiuretic hormone (ADH) signal the cells to increase aquaporin expression in response to dehydration or high plasma osmolality, enhancing water reabsorption to conserve body fluids.

Physiological Responses to Hydration Status

The body's physiological responses to hydration status determine the number of aquaporins present in kidney tubule cells. After intense exercise in hot conditions, the body is likely to be dehydrated, prompting increased aquaporin insertion to maximize water reabsorption. In contrast, after consuming a large amount of water, the body would reduce aquaporin levels to excrete the excess fluid.