Problem 13 - Campbell Biology Concepts & Connections

Question

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.

Step-by-Step Solution

Answer

After a long run on a hot day.

Step 1: Understanding the Function of Aquaporins

Aquaporins are water channels in the plasma membrane that allow water to pass through cells more efficiently. They play a crucial role in the reabsorption of water in kidney tubule cells.

Step 2: Analyze Each Situation

To determine when tubule cells would have the most aquaporins, consider the body's need to conserve or expel water in each situation:- After a long run on a hot day, the body loses a lot of water through sweat, so it needs to reabsorb more water back into the body from the urine.- Right after a large meal, the body's immediate concern is digestion, not necessarily water reabsorption.- After drinking a large bottle of water, the body has excess water and needs to expel it, reducing the need for reabsorption.

Step 3: Deduce the Most Critical Situation for Aquaporins

Since the body needs to conserve water after a long run on a hot day due to high water loss, tubule cells will insert the most aquaporins into their plasma membranes to reabsorb as much water as possible.

Key Concepts

Aquaporins

Aquaporins are specialized water channels in cell membranes. They allow water molecules to pass through cells efficiently and play a crucial role in maintaining our body's water balance. These channels are particularly important in the kidneys, where they facilitate the reabsorption of water from urine back into the bloodstream. This helps the body retain necessary fluids, especially in situations where there is a high demand for water, such as after intense physical activity or in the absence of adequate hydration. Aquaporins can be inserted or removed from the plasma membrane in response to the body's hydration needs, making them an essential component in water regulation.

Kidney Function

The kidneys have the primary function of filtering blood, removing waste products, and managing water balance. Within the kidneys, the nephron is the primary functional unit that performs these critical roles. Each nephron contains a tubule system where reabsorption and secretion take place. Cells lining these tubules are equipped to reabsorb water and essential nutrients while ensuring waste products are excreted. This reabsorption process is aided by the presence of aquaporins, which allow for efficient water movement back into the bloodstream.
The coordination of aquaporins ensures that the body maintains a stable internal environment, adapting to varying water needs during different activities.

Water Balance

Water balance is crucial for maintaining homeostasis in the body. Homeostasis refers to the stable conditions needed for cells to function optimally. Through mechanisms involving the kidneys, the body can regulate water intake and output, adapting to conditions that either increase water loss or water intake.
For example, after physical activities like a long run on a hot day, the body loses substantial water through sweat, so maintaining water balance becomes vital. The insertion of aquaporins in kidney tubule cells increases, promoting water reabsorption to conserve body fluids. However, after consuming a large meal or drinking plenty of water, the body's need for reabsorption decreases, and fewer aquaporins are inserted, allowing for excess water to be excreted.