Question

Using the principles of osmosis, explain why movement of \(\mathrm{Na}^{+}\)through a plasma membrane is followed by movement of water. Use this concept to explain the rationale on which oral rehydration therapy is based.

Short answer

Osmosis is the movement of water across a selectively permeable membrane from a region of low solute concentration to a region of high solute concentration. When Na+ ions move across the plasma membrane, they create a concentration gradient, causing water to move from the extracellular space into the cell to balance the concentration difference. Oral rehydration therapy involves consuming a solution containing electrolytes and glucose to maintain fluid and electrolyte balance. The presence of Na+ ions and glucose in the solution aids in the absorption of water in the intestines, allowing the body to rehydrate more effectively and recover from diarrhea and vomiting.

Step-by-step solution

Osmosis is the movement of water molecules across a selectively permeable membrane from a region of low solute concentration to a region of high solute concentration, ultimately aiming to equalize the solute concentration on both sides of the membrane. In the context of this exercise, the plasma membrane acts as the selectively permeable membrane. #Step 2: Movement of Na+ ions and water across the plasma membrane#

When sodium ions (Na+) move across the plasma membrane, they create a concentration gradient, with a higher concentration of Na+ inside the cell. According to the principles of osmosis, water molecules will move across the membrane to equalize this gradient. In this case, water will move from the extracellular space (low Na+ concentration) into the cell (high Na+ concentration) to balance the concentration difference. #Step 3: Applying the concept to oral rehydration therapy#

Oral rehydration therapy is a treatment method for dehydration, particularly in cases of diarrhea and vomiting. It involves the intake of a solution containing electrolytes (e.g., sodium, chloride, potassium) and glucose to maintain a proper balance of fluid and electrolytes in the body. The presence of Na+ and glucose in the rehydration solution aids the absorption of water in the intestines. #Step 4: Rationale behind oral rehydration therapy#

When a person consumes the rehydration solution containing Na+ ions and glucose, it creates a higher concentration of solutes in the intestinal lumen. According to the principle of osmosis, water will move from the intestinal tissue (low solute concentration) to the lumen (high solute concentration) to equalize the concentration difference. This allows the body to absorb water more effectively, leading to rapid rehydration and recovery from diarrhea and vomiting.

Key concepts

Plasma Membrane Permeability

The plasma membrane, often referred to as the cell's gatekeeper, regulates permeability—its ability to allow substances to pass in and out. This selectively permeable nature is crucial for maintaining the cell's internal environment.

Think of the plasma membrane as a bouncer at a club, deciding who's on the guest list, which in cellular terms means which molecules can pass through. Sodium ions (Na+), for example, are like VIP guests that need a proper pass—in cells, they require specific channels or transporters.

Sodium Ions (Na+) Transport

Sodium ions are essential in numerous physiological processes, including nerve impulse transmission and muscle contractions. Their movement across the plasma membrane is not a random event but a highly orchestrated process. It often relies on proteins such as ion channels or pumps that provide a passage or actively transport Na+ into or out of cells.

Because sodium carries a charge, its movement can also affect the electrical status of a cell, which has significant implications for how cells communicate and function.

Oral Rehydration Therapy

Oral rehydration therapy (ORT) is a life-saving treatment for dehydration due to illnesses like diarrhea. It's a mix of clean water, salts, and sugar that helps replenish lost fluids and electrolytes.

Here's the fascinating bit: the glucose in ORT solutions works hand in hand with sodium to improve water absorption through the intestinal wall—a kind of biochemical teamwork that exemplifies the harmony within our bodies. This therapy affirms how a thorough understanding of biological principles can lead to simple yet effective medical treatments.

Concentration Gradient

A concentration gradient is like a hill - molecules naturally 'roll down' from areas of high concentration (top of the hill) to low concentration (bottom). It's a driving force behind many biological processes, including osmosis, where the goal is equal levels on both sides.

Cells actively work to maintain certain concentration gradients, especially for ions like Na+, as these are vital for functions such as transmitting nerve signals or muscle contractions.

Water Molecule Movement

Water molecules are constantly on the move, jiggling and tumbling about. In osmosis, they sneak through the plasma membrane from where there's more water (and less of everything else) to where there's less water (and more of those other things like Na+ and glucose).

Imagine a dance floor where water molecules are constantly swapping partners (Na+ or glucose) to maintain balance in their concentrations, ensuring the party (our bodies) keeps going on smoothly.

Electrolyte Balance

Electrolytes are the body's minerals that have an electric charge. They're like the batteries that keep cellular phones running, ensuring our cells function properly. Sodium, potassium, and chloride are some of the major players.

Keeping the right balance of electrolytes is like tightrope walking—it's all about maintaining that perfect equilibrium to support muscle function, regulate pH levels, and manage fluid balance. That's why when we lose too much, as through sweating or sickness, an electrolyte solution can help us restore that delicate balance and keep our metaphorical tightrope walker upright.