Fluid and Electrolyte Balance

Fluid Balance

  • Definition: Regulation of the body’s fluid compartments to maintain a stable internal environment.

  • Importance: Affects cellular metabolism, temperature regulation, and delivery of oxygen/nutrients.

  • Consequences of Imbalance: Changes in volume/concentration can negatively affect vital life processes.

Fluid Compartments

  • Intracellular Fluid (ICF): Fluid inside the cells.

  • Extracellular Fluid (ECF): Fluid outside the cells, further divided into:

    • Intravascular Space: Inside blood vessels.

    • Interstitial Space: Between cells.

    • Transcellular Space: Containing fluids like pericardial, cerebrospinal, and synovial fluid.

  • Composition: Composed mainly of water and solutes.

    • Total Body Water: Over half of an adult's body weight is water.

Solutes

  • Small Solutes: Easily cross cell membranes; includes gases (O2, CO2), glucose, and electrolytes.

  • Large Solutes: Cannot easily cross membranes; includes plasma proteins and blood components (red blood cells, white blood cells, platelets).

Electrolytes Overview

  • Definition: Charged molecules (ions) crucial for various bodily functions.

  • Functions: Transmission of nerve impulses, muscle contraction, and fluid osmolality maintenance.

  • Homeostasis: Essential for normal body functioning.

Major Electrolytes

  • Sodium (Na+):

    • Main cation in ECF.

    • Maintains osmolality, blood volume, and pressure.

    • Normal value: 135 to 145 mEq/L.

  • Potassium (K+):

    • Main cation in ICF.

    • Vital for maintaining resting membrane potential.

    • Normal range: 3.5 to 5 mEq/L.

  • Calcium (Ca2+):

    • Important for neurotransmitter release, muscle contraction, and blood clotting.

    • Normal range: 8.5 to 10.5 mg/dL.

  • Magnesium (Mg2+):

    • Influences cardiac and skeletal muscle function.

    • Acts as a cofactor in enzyme reactions.

    • Normal range: 1.3 to 2.1 mEq/L.

  • Phosphate (PO43-):

    • Works with calcium for bones and teeth formation.

    • Essential for ATP and nucleotides (DNA/RNA).

    • Normal range: 1.7 to 2.6 mEq/L.

Electrolyte Movement

  • Active Transport: Uses ATP to move electrolytes against concentration gradient.

    • Example: Sodium-potassium pump (3 Na+ out, 2 K+ in).

  • Diffusion: Passive movement down the concentration gradient (higher to lower).

    • Simple Diffusion: Molecules like O2 move across membranes without energy.

    • Facilitated Diffusion: Requires channel proteins for ions like sodium or potassium to cross membranes.