What are the two main fluid compartments of the body?
Intracellular fluid (ICF) and extracellular fluid (ECF), separated by cell membranes.
What are the two components of extracellular fluid (ECF)?
Interstitial fluid volume (IFV) and plasma volume (PV), separated by capillary endothelium.
Approximately what proportion of total body weight is total body water (TBW) in males and females?
About 60% in males and 50% in females.
How much of a 70 kg male’s body weight is total body water, intracellular fluid, and extracellular fluid?
TBW = 42 L; ICF = 28 L (≈ 66% of TBW); ECF = 14 L (≈ 33% of TBW).
How much of a 56 kg female’s body weight is total body water, intracellular fluid, and extracellular fluid?
TBW = 28 L (50% of BW); ICF = 16.8 L (30% of BW); ECF = 11.2 L (20% of BW).
What fraction of the ECF is plasma volume (PV) and interstitial fluid volume (IFV)?
PV = ¼ of ECF (≈ 3.5 L); IFV = ¾ of ECF (≈ 10.5 L).
What percentage of the ECF does lymph represent?
Approximately 3% of ECF.
What physical barrier separates the ICF and ECF?
The cell membrane.
What physical barrier separates plasma volume and interstitial fluid?
The capillary endothelium.
Why do males typically have higher total body water than females?
Males generally have more lean tissue (which contains more water), while females have higher body fat content (which contains less water).
What does concentration mean in physiology?
It’s the amount of a substance per given volume — typically expressed as mass / volume.
What is molarity (M)?
The number of moles of a solute per liter (L) of solution, expressed as mol/L or mmol/L.
What is osmolarity?
The total number of solute particles per liter of solution (expressed as mOsmol L⁻¹).
How does osmolality differ from osmolarity?
Osmolality = number of solute particles per kg of water;
Osmolarity = number of solute particles per L of solution
- they can both be used interchangeably
Which is temperature-dependent: osmolarity or osmolality?
- Osmolarity is temperature-dependent because liquid volume changes with heat; osmolality is temperature-independent and if often used in sports and fitness nutrition
At equilibrium, what happens to the hydrostatic pressure in Compartment A?
It increases until it balances (equal and opposite) the osmotic pressure created by the solute in Compartment A.
What is osmosis?
The movement of water (H₂O) across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration.
What determines osmotic pressure?
The number of dissolved particles—independent of their size, charge, or mass.
What is equivalence in relation to charged solutes?
- It expresses concentration based on the charge of ions, that usually disscoiate to more than 1 particle when put in solvent
What is the equivalent concentration for 154 mmol/L Na⁺ or Cl⁻, both with valence = 1?
154 mEq/L for each ion.
How many milliequivalents per liter (mEq/L) does 154 mmol/L of Ca²⁺ equal?
154mmol/L×2=308mEq/L.
How does valence affect the equivalent combining power of ions?
The higher the valence, the greater the combining power; e.g., Ca²⁺ has twice the combining power of Na⁺.
Which ions account for > 95 % of plasma osmolality?
Na⁺ and its accompanying anions Cl⁻ and HCO₃⁻
In a 70 kg male, what are normal compartment volumes?
ICF ≈ 28 L (66% x 42) and ECF ≈ 14 L (33% x 42) (total body water = 42 L)
