Body Fluid Compartments Quiz

Study Notes

Water is the largest component of the human body, making up 60% of body weight in a normal adult.
Total body water (TBW) is divided into:
- Intracellular water: 65% of TBW
- Extracellular water: 35% of TBW, further divided into:
  - Plasma: 20% of ECF
  - Interstitial fluid: 80% of ECF
Water in blood plasma accounts for roughly 90% of its volume.
Functions of water in the body:
- Provides structure and form to all tissues.
- Serves as a solvent for nutrients, wastes, and chemical reactions.
- Facilitates the transport of nutrients and waste via blood and the lymph system.
- Essential for hydrolysis and metabolism.
- Acts as a lubricant for joints and digestion.
- Regulates body temperature through perspiration evaporation.

Water gain occurs through:
- Ingestion of liquids and moist foods: 2300mL/day
- Metabolic synthesis of water during cellular respiration: 200mL/day
Water loss occurs through:
- Kidneys: 1500mL/day
- Skin evaporation: 600mL/day
- Lungs exhalation: 300mL/day
- Feces: 100mL/day

Maintaining water balance is vital for health.
Water balance is achieved when water intake equals water output.
Clinically significant problems arise from fluid loss, retention, or redistribution.
Management of these problems is often urgent and requires biochemical analysis.
Both the internal (distribution between body compartments) and external (input vs. output) balances are essential.

Over-hydration: Occurs when fluid accumulates in body compartments (water intake > water loss).
Dehydration: Occurs when fluid is lost from body compartments (water loss > water intake).
- Loss of intracellular fluid leads to cellular dysfunction, lethargy, confusion, and coma.
- Loss of extracellular fluid (e.g., bleeding) can lead to collapse and shock.

Low water intake
High water loss
Diuresis (e.g., diabetes mellitus, diabetes insipidus, renal failure)
- Renal failure leads to failure to reabsorb water, producing highly diluted urine.
Diarrhea
Excessive sweating and evaporation (via skin)
Hemorrhage

Electrolytes are substances that dissociate into ions when dissolved in a solution, allowing them to conduct electricity.
Cation: Positively charged electrolyte.
Anion: Negatively charged electrolyte.
Electrolyte concentration is expressed in milliequivalents per liter (mEq/L).

Intracellular Fluid (ICF)
- Predominant Cations: Potassium (K+), Magnesium (Mg+)
- Predominant Anions: Phosphate (HPO4--), Protein
Extracellular Fluid (ECF)
- Predominant Cations: Sodium (Na+), Calcium (Ca+)
- Predominant Anions: Chloride (Cl-), Bicarbonate (HCO3-)

For each fluid compartment, the number of cations must equal the number of anions to maintain electrical neutrality.

ECF: Sodium (Na+) and Chloride (Cl-) are the predominant cations and anions, respectively.
ICF: Potassium (K+) and Phosphate (HPO4--) are the predominant cations and anions, respectively.