Sodium and Potassium in Body Fluids

What percentage of extracellular cations does sodium Na+ represent?

What is the primary mechanism that prevents sodium Na+ from reaching equilibrium between the extracellular fluid and inside the cell?

How many sodium Na+ ions are moved out of the cell by the Na+,K+ ATPase ion pump?

What happens to water when sodium Na+ is actively removed from the cell?

What is the normal plasma osmolality value approximated in mmol/L?

Which of the following statements is true regarding potassium K+ compared to sodium Na+?

Sodium (Na+) in Extracellular Fluid (ECF)

Sodium (Na+) is the most abundant cation in the ECF, making up 90% of all extracellular cations.
It significantly influences plasma osmolality.
Normal plasma osmolality is approximately 295 mmol/L, with 270 mmol/L contributed by Na+ and associated anions.
The concentration of Na+ is much higher outside cells compared to inside.
Passive diffusion of Na+ across cell membranes would lead to equilibrium.
Cells utilize active transport systems, like ATPase ion pumps, to maintain this concentration gradient.

Potassium (K+) in Intracellular Fluid

Potassium (K+) is the major intracellular cation.
Like Na+, K+ would eventually diffuse across the cell membrane to reach equilibrium.
The Na+/K+ ATPase ion pump actively transports ions.
This pump moves three Na+ ions out of the cell for every two K+ ions moving in, using ATP. This process converts ATP to ADP.

Osmotic Balance and Cell Integrity

Water follows the movement of electrolytes across cell membranes.
Continuous removal of Na+ from the cell prevents osmotic rupture of the cell by drawing water out.

This quiz covers the roles of sodium and potassium ions in extracellular and intracellular fluids, their influence on plasma osmolality, and the mechanisms of active transport through ion pumps such as the Na+/K+ ATPase. Understanding these concepts is crucial for comprehending osmotic balance and cell integrity.