Fluid and Electrolyte Balance

Fluid Compartments

• Humans are mostly water.

• Primary fluid areas:

  • Intracellular Fluid (ICF): Within cells; electrolytes manage fluid movement.

  • Extracellular Fluid (ECF): Outside cells.

    • Intravascular: Within blood vessels.

    • Interstitial: Between cells.

Fluid Balance: Intake & Output

• Output: Primary means is urine; also perspiration, exhalation, feces.

• Intake: Drinking, food, metabolism.

• Balance between intake and output is essential for health.

Fluid Regulation Organs & Hormones

• Kidney: Primary organ; resorbs fluid after filtration, excretes excess fluid as urine.

• Endocrine Glands: Hypothalamus via pituitary gland controls body fluid.

• Hormones (Pituitary osmoreceptors control release of):

  • Renin

  • Aldosterone

  • Antidiuretic Hormone (ADH): Decreases urine output; decrease in ADH increases urine output.

Fluid Imbalances

• Excess Fluid Loss (ECF Deficit):

  • Causes: Vomiting/diarrhea, burns, excessive GI suctioning, diuresis.

  • Signs/Symptoms: Decreased BP, increased HR/RR, oliguria, thirst, poor skin turgor, $Na^+$ exceeding $150$ mEq/L.

• Intracellular Fluid Deficit:

  • Causes: Decreased water intake, fever, renal malfunction, decreased ADH secretion.

• Excess Fluid Retention (ECF Excess):

  • Causes: Renal disease, cirrhosis, cardiac insufficiency, overhydration.

  • Signs/Symptoms: Increased BP, increased HR/RR, inspiratory crackles, neck vein distention, peripheral edema, $Na^+$ less than $130$ mEq/L.

Major Electrolytes

• Chemicals that dissociate into electrically charged ions (cations/anions) in water.

• Functions: Fluid distribution, neuromuscular impulses, aid acid-base balance, transportation, cellular metabolism.

• Potassium ($K^+$):

  • Major ICF cation; serum $3.5$ - $5.0$ mEq/L.

  • Buffer, effects neuromuscular activities; kidney regulated.

• Sodium ($Na^+$):

  • Major ECF cation; serum $136$ - $145$ mEq/L.

  • Buffer, controls body fluid balance ("where sodium goes, water soon follows"); kidney regulated.

• Chloride ($Cl^-$):

  • Major ECF anion; serum $100$ - $106$ mEq/L.

  • Buffer, helps maintain blood volume/pressure; kidney regulated.

• Calcium ($Ca^{2+}$):

  • ICF cation, mostly in bones; serum $4.5$ - $5.5$ mEq/L.

  • Skeletal mineral content, vital for muscle contractions and cell membrane integrity.

• Magnesium ($Mg^{2+}$):

  • Cation; serum $1.3$ - $2.1$ mEq/L.

  • Important for muscle function, cardiac conduction, energy production, protein synthesis.

Other Important Ions & Factors

• Bicarbonate ($HCO_3^-$):

  • ECF and ICF; serum $22$ - $26$ mEq/L.

  • Major acid-base body buffer; kidney regulated.

• Phosphate ($HPO_4^{2-}$):

  • Main ICF anion, mostly in bones/teeth; serum $1.2$ - $2.3$ mEq/L.

  • Aids cellular energy metabolism, main urinary buffer.

• Sulfate ($SO_4^-$):

  • Part of amino acids; detoxifies body, assists immune system.

• Protein: Essential for maintaining lean body mass; RDA approx. $0.8$ g/kg/day.

• Organic Acids: Derived from diet; generate cellular energy, provide building blocks for cell function.