Sodium and Potassium

Sodium (Na⁺) and Potassium (K⁺) in the Human Body

• Normal plasma levels:

  • Sodium: 135–145 mEq/L

  • Potassium: 3.5–5.0 mEq/L

• Main roles:

  • Na⁺: Major extracellular cation – maintains extracellular fluid volume, osmotic pressure, and nerve impulse transmission.

  • K⁺: Major intracellular cation – maintains resting membrane potential, nerve conduction, and muscle contraction.

• Transport: Maintained by Na⁺/K⁺-ATPase pump (3 Na⁺ out, 2 K⁺ in per ATP).