Question

Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is the principal anion?

(a) HCO3-
(b) Cl-
(c) PO43-
(d) OH-

Answer 1

Chloride ions (Cl-) serve as the principal anion, counterbalancing the high sodium concentration in the extracellular environment, ensuring cellular electroneutrality and function.

Step-by-step explanation:

In the extracellular environment, maintaining electroneutrality is crucial due to the high sodium ion concentration. The principal anion responsible for neutralizing the positive charge of sodium is chloride (Cl-). This is evident in the balance of cations and anions, where the negatively charged chloride ions work to counterbalance the positive charge carried by sodium ions.

Chloride ions play a pivotal role in preserving the electrical neutrality essential for cellular functions. The relationship between sodium and chloride ions helps establish the resting membrane potential of cells, influencing various physiological processes such as nerve conduction and muscle contraction. The negatively charged chloride ions effectively balance the extracellular environment's positively charged sodium ions, contributing to the overall stability of cellular function.

In physiological terms, the extracellular concentration of chloride ions is approximately 100 mM, emphasizing their significance in counterbalancing the predominant cation, sodium. This delicate equilibrium is essential for maintaining cellular homeostasis and ensuring proper physiological function. The chloride ion's role as the principal anion in the extracellular environment underscores its importance in supporting fundamental cellular processes.

Answer 2

Chloride (Cl-) is the principal anion responsible for neutralizing the high extracellular sodium ion concentration, helping to maintain electrical neutrality in the extracellular fluid (option b).

Step-by-step explanation:

The question concerns the neutralization of the extracellular environment with respect to its ionic composition. Specifically, it deals with which principal anion is responsible for balancing the high sodium ion concentration in the extracellular fluid (ECF). Based on the information provided, chloride (Cl-) is the predominant extracellular anion. It functions importantly to balance out the cations, particularly the sodium ions (Na+), in the ECF, thereby maintaining the electrical neutrality of this fluid. The sodium-potassium pump also plays a crucial role in this process by actively pumping sodium ions out of the cell and potassium ions into the cell, using the energy supplied by ATP, further contributing to the charge balance.

Hence, the answer is option b.