Body Fluids and Fluid Compartments

Vocabulary flashcards covering body fluid compartments, fluid measurement methods, markers, equations, and clinical conditions like dehydration and water intoxication.

Body Fluid Compartments Diagram

Diagram showing fluid exchange and volumes for an average $70\text{ kg}$ person: plasma ($3.0\text{ L}$) and interstitial fluid ($11.0\text{ L}$) constituting extracellular fluid ($14.0\text{ L}$), and intracellular fluid ($28.0\text{ L}$).

Osmolar Substances in ECF and ICF Table

Comparison table of solute concentrations showing total mOsm/L for Plasma ($301.8$), Interstitial ($300.8$), and Intracellular ($301.2$) fluids, with corrected osmolar activities of $282.0$, $281.0$, and $281.0\text{ mOsm/L}$ respectively.

Indicator Dilution Method Formula

Formula used to calculate an unknown fluid compartment volume: $\text{Volume B} = \frac{\text{Volume A} \times \text{Concentration A}}{\text{Concentration B}}$

Insensible Water Loss

Daily water loss occurring via evaporation through the respiratory tract and skin, accounting for about $700\text{ ml/day}$.

Extracellular Fluid (ECF)

All fluid outside the cells, making up about $20$% of body weight (about $14\text{ L}$ in a $70\text{ kg}$ man), composed of interstitial fluid ($\frac{3}{4}$ or $11\text{ L}$) and blood plasma ($\frac{1}{4}$ or $3\text{ L}$).

Intracellular Fluid (ICF)

Fluid found inside the cells, constituting about $40$% of body weight and approximately $28\text{ L}$ of total body water.

Transcellular Fluid

Specialized types of extracellular fluid including synovial fluid, fluid in peritoneal, pericardial, and intraocular spaces, as well as cerebrospinal fluid.

Indicator Dilution Method

A technique used to measure total body water, ECF volume, and plasma volume by administering a known quantity of a non-toxic marker substance or dye into a fluid compartment and measuring its final concentration after thorough mixing.

Total Body Water Markers

Substances such as radioactive water ($^3\text{H}_2\text{O}$ or tritium) or heavy water ($^2\text{H}_2\text{O}$ or deuterium) that mix with fluids of all compartments within a few hours to measure total body water.

ECF Markers

Substances that disperse in plasma and interstitial fluid but do not readily permeate the cell membrane, including radioactive sodium, radioactive chloride, radioactive iothalamate, thiosulfate ion, and inulin.

Plasma Volume Markers

Substances that bind strongly to plasma proteins and do not diffuse into the interstitium, such as serum albumin labeled with radioactive iodine ($^{125}\text{I-albumin}$) and Evans blue dye (also called $\text{T-1824}$).

Intracellular Volume Calculation

The mathematical equation used to determine intracellular volume indirectly: $\text{Intracellular volume} = \text{Total body water} - \text{Extracellular volume}$

Interstitial Fluid Volume Calculation

The mathematical equation used to calculate interstitial fluid volume indirectly: $\text{Interstitial Fluid Volume} = \text{ECF Volume} - \text{Plasma Volume}$

Total Blood Volume Calculation

The equation used to calculate total blood volume using plasma volume and hematocrit: $\text{Total Blood Volume} = \frac{\text{Plasma volume}}{1 - \text{Haematocrit}}$

Isotonic Dehydration

A form of dehydration involving a balanced loss of solute ($\text{Na}^+$) and water, typically caused by diarrhea and vomiting.

Hypotonic Dehydration

A form of dehydration characterized by the loss of more solute ($\text{Na}^+$) than water, often resulting from excessive use of diuretics.

Hypertonic Dehydration

A form of dehydration characterized by the loss of more water than solute, such as during a fever.

Water Intoxication

A condition characterized by a significant increase in body water content when fluid intake exceeds excretion; also known as hyperhydration, overhydration, or water poisoning.

Delirium

An extreme mental condition characterized by a confused state and illusion, which can occur in severe cases of water intoxication.

Seizures

Sudden uncontrolled involuntary muscular contractions that occur in severe conditions of water intoxication.

Coma

A profound state of unconsciousness in which a person fails to respond to external stimuli and cannot perform voluntary actions.