Body Fluid Compartments and Homeostasis Vocabulary

Vocabulary flashcards covering key terms related to body fluid compartments, osmotic concepts, distribution volume measurements, and water/electrolyte balance.

Osmolarity

The concentration of a solution expressed as the total number of osmotically active solute particles per liter of solution ($\text{osmol/l}$ or $\text{mosmol/l}$).

Osmolality

The concentration of a solution expressed as the total number of osmotically active solute particles per kilogram of water ($\text{osmol/kg water}$).

Tonicity

The effect a solution has on cell volume, taking into consideration both solute concentration and the ability of a solute to cross the cell membrane.

Isotonic Solution

A solution with an osmotic concentration equal to normal body fluids ($\sim 300\,\text{mosmol/l}$) that causes no net change in cell volume.

Hypotonic Solution

A solution with a lower osmotic concentration than cell contents, causing water to enter the cell and leading to swelling or cell lysis.

Hypertonic Solution

A solution with a higher osmotic concentration than cell contents, causing water to leave the cell and leading to cell shrinkage.

Total Body Water (TBW)

The total volume of body fluid, accounting for approximately $60\%$ of total body weight in males and $50\%$ in females.

Intracellular Fluid (ICF)

The fluid compartment contained within cells, making up $67\%$ of Total Body Water, with $K^+$ as its major cation.

Extracellular Fluid (ECF)

The fluid compartment outside cells, making up $33\%$ of Total Body Water, consisting primarily of interstitial fluid ($\sim 80\%$) and plasma ($\sim 20\%$).

Distribution Volume

The calculated volume ($V$) of a fluid compartment determined via the dilution principle: $\text{Distribution volume (litres)} = \frac{Q_X\,(\text{mol})}{[X]\,(\text{mol/litre})}$ where $Q_X$ is the quantity of tracer added and $[X]$ is its equilibrium concentration.

Tracer

A measurable indicator substance used to determine fluid compartment size, such as $^3\text{H}_2\text{O}$ for TBW, inulin for ECF, and labeled albumin for plasma volume.

Insensible Water Loss

Unregulated, continuous water loss occurring through the skin ($350\,\text{ml/day}$) and lungs ($350\,\text{ml/day}$).

Sensible Water Loss

Measurable or regulated water output consisting of sweat ($100\,\text{ml/day}$), feces ($200\,\text{ml/day}$), and urine ($1500\,\text{ml/day}$).

Fluid Shift

The physical movement of water between the intracellular fluid (ICF) and extracellular fluid (ECF) in response to an osmotic gradient.

Electrolyte Balance

The physiological state maintained when the rate of gain of individual electrolytes equals their rate of loss.