Body Fluids Overview

Body Fluids

  • Total Body Water: Approximately 60% of body weight.
    • Intracellular Volume (ICF): 40% of total body water (28L).
    • Extracellular Volume (ECF): 20% of total body water (14L).
      • Interstitial Fluid: 15%
      • Plasma Volume: 5% (3.5L).

Fluid Compartments

  • Intracellular Fluid (ICF): Fluid found inside cells.
  • Extracellular Fluid (ECF): Fluid outside of cells, consists of:
    • Plasma: Approx. 20% of ECF, found in blood.
    • Interstitial Fluid: 80% of ECF, found between cells (includes aqueous humor, cerebrospinal fluid, etc.).

Blood Volume and Functions

  • Blood volume constitutes about 7-8% of body weight.

    • Child: 80-90 ml/kg
    • Adult: 70 ml/kg

  • Composition of blood:

    • Plasma: 60%
    • Blood Cells: 40% (RBC, WBC, Platelets).

  • Functions of Blood:

    • Maintain homeostasis (pH buffering, regulation of body temperature).
    • Transport of gases, nutrients, hormones, and waste.
    • Host defense mechanisms (immune response and coagulation).

Blood Components

  • Water: 93-95% in plasma; acts as a solvent and maintains osmotic pressure.
  • Electrolytes: Includes Na⁺, K⁺, Mg²⁺, Cl⁻, HCO₃⁻; crucial for cell shape, and pH regulation.
  • Proteins:
    • Albumin: 40-48 g/L; maintains osmotic pressure
    • Globulin: 15-30 g/L; involved in immune response.
    • Fibrinogen: 2-4 g/L; essential for blood coagulation.

Electrolytes and Their Role

  • ECF:
    • Cation: Na⁺ (important for muscle contraction and nerve impulse transmission).
    • Anion: Cl⁻ (regulates osmotic pressure).
  • ICF:
    • Cation: K⁺ (vital for resting membrane potential and pH regulation).
    • Anion: Proteins and phosphates.

Composition of Body Fluids

  • ECF vs ICF:
    • ECF:
      • Na⁺: 142 mmol/L
      • Cl⁻: 105 mmol/L
      • Osmolarity: 290 mosm/L
    • ICF:
      • K⁺: 160 mmol/L
      • Phosphates: 100 mmol/L
      • Osmolarity: 290 mosm/L

Fluid Regulation

  • Regulated by:
    • ADH (Antidiuretic Hormone): Increases water reabsorption in kidneys.
    • Aldosterone: Increases sodium reabsorption.
    • Atrial Natriuretic Factor: Inhibits renin and increases sodium excretion.

Dehydration and Management

  • Epidemiology: Common issue, affecting pediatric admissions; causes include excessive sweating, vomiting, and inadequate intake.
  • Signs to look for:
    • In adults: headache, fatigue, dark urine.
    • In infants: dry mouth, lack of tears, dry diapers.
  • Management: Replacement of fluids and electrolytes based on needs.

Electrolyte Disorders

  • Hyponatremia: Sodium < 135 mEq/L, caused by diluted blood from excess water.
    • Symptoms: headache, confusion, seizures.
  • Hypernatremia: Sodium > 145 mEq/L, causes thirst and potential brain problems.
  • Hypokalemia: Serum K⁺ < 3 mEq/L; affects cardiac function.
  • Hyperkalemia: High potassium is life-threatening; symptoms include muscle twitches and arrhythmias.

Specialized Fluids

  • Cerebrospinal Fluid (CSF): Provides cushioning and regulates intracranial pressure.
  • Milk: Contains proteins, lipids; provides nutrients for infants.
  • Amniotic Fluid: Protective medium for the fetus.
  • Tears: Lubricate and protect the eye from infection.
  • Sweat: Involved in thermoregulation; electrolyte content can vary based on hydration status.