body fluids & their disturbances

Comprehensive vocabulary flashcards covering body fluid distribution, measurement, and clinical disturbances based on the lecture notes.

total body water (TBW)

the total amount of water in a person's body

• consisting of ⅔ intracellular fluid (ICF) and ⅓ extracellular fluid (ECF)

• typically accounting for about 60% of body weight in adults

intracellular fluid (ICF)

the fluid present inside the cells (cytoplasm) comprising ⅔ of the total body water (TBW)

• major cations - K⁺ & Mg²⁺

• major anions - proteins & phosphates (PO₄³⁻)

extracellular fluid (ECF)

the fluid present outside the cells comprising ⅓ of the total body water (TBW)

• consisting of plasma (¼) and interstitial fluid (¾) separated by capillary endothelium

  • plasma - fluid portion of blood

  • interstitial fluid - fluid in spaces between cells in tissues/organs

• contains high concentrations of Na⁺, Cl⁻, & bicarbonate (HCO₃)

plasma

the fluid portion of blood that makes up about ¼ of the extracellular fluid (ECF) volume

• contains clotting factors

• has large amount of proteins (impermeable through capillary membrane)

interstitial fluid

fluid found in spaces between cells in tissues and organs comprising about ¾ of the extracellular Fluid (ECF) volume

60-40-20 rule

a principle used to estimate body fluid distribution

• approximately 60% of total body weig

  ht is water of which

  • 40% is intracellular fluid

  • 20% is extracellular fluid → (25% plasma + 75% interstitial fluid)

blood volume

the total amount of blood circulating within the cardiovascular system

• typically about 7-8% of body weight

• includes plasma and cellular components (red blood cells, white blood cells, & platelets)

• calculated as $\frac{\text{Plasma volume}}{1 - Hct}$

hematocrit (Hct)

the fractional concentration of red blood cells (RBCs) in the blood relative to the total blood volume

$$\frac{\text{Plasma volume}}{1 - Hct}$$

blood volume

dilution method

a quantitative approach used to determine the volume of a specific body fluid compartment by tracking how an indicator distributes within that compartment

• relies on a marker that stays exclusively within the compartment being measured

• after equilibration → indicator concentration reflects compartment volume

• $$\text{Volume of comparment (mL) }=\frac{\text{Amount of marker injected (mg)}}{\text{Concentration of the marker (mg/mL)}}$$

$\textcolor{black}{\frac{\text{Amount of marker injected (mg)}}{\text{Concentration of the marker (mg/mL)}}}$

volume of the fluid compartment (dilution method)

D₂O (deuterium oxide), tritiated water, antipyrine, or urea

markers for total body water (TWB)

inulin, mannitol, sodium, or sucrose

markers for ECF volume

radioactive albumin or Evans blue

markers for plasma volume

ICF volume calculation

$$\textcolor{blue}{\bm{TBW-ECF}}$$

• need two markers

  • TWB → D₂O (deuterium oxide), tritiated water, antipyrine, or urea

  • ECF → inulin, mannitol, sodium, or sucrose

interstitial fluid (IF) volume calculation

$$\textcolor{blue}{\bm{ECF-}}\textcolor{blue}{\text{Plasma volume}}$$

• need two markers

  • ECF → inulin, mannitol, sodium, or sucrose

  • plasma volume → radioactive albumin or Evans blue

tonicity

the effective osmotic pressure gradient of a solution determining the direction of water movement across a semipermeable membrane

• influences cell shape and function based on the relative concentrations of solutes inside and outside the cell

isotonic solution

a solution that does not change the volume of the body cells

• equal concentrations of solutes on both sides of the cell membrane → no net water movement

hypertonic solution

a solution that causes body cells to shrink

• due to a higher concentration of solutes outside the cell → net water movement out of the cell

hypotonic solution

a solution that causes body cells to swell

• due to a lower concentration of solutes outside the cell → net water movement into the cell

steady state osmolarity

a condition where the concentration of solutes in the body fluids remains stable

• maintains equilibrium between intracellular and extracellular fluids

• ~ 300 mOsm/L

plasma osmolarity

the total concentration of dissolved osmoles in plasma reflecting the osmolarity of both the extracellular and intracellular fluid compartments

• primarily determined by impermeant ECF osmoles → NaCl contributes most of the effective osmolarity of plasma

• normal plasma osmolarity ≈ 280–295 mOsm/L

estimated plasma osmolarity (P_osmolarity)

a rapid clinical approximation of plasma osmolarity based on the fact that sodium salts dominate the effective osmoles of the ECF

• twice the [Na⁺] = good index

• calculated as 2 × plasma sodium concentration

accurate plasma osmolarity

a calculated measure of plasma osmolarity that includes all major solutes contributing to osmotic pressure

• $$\textcolor{blue}{P_{osm}=2([Na^{+}])+\frac{[glucose]}{18}+\frac{BUN}{2.8}}$$

  • glucose and BUN terms convert mg/dL → mmol/L

• accounts for osmoles that become significant in disease states:

  • ↑ glucose → uncontrolled diabetes mellitus

  • ↑ BUN → chronic renal failure

$$P_{osm} = 2([Na^+]) + \frac{[glucose]}{18} + \frac{BUN}{2.8}$$

accurate plasma osmolarity

body fluid disturbances

changes in the composition or volume of body fluids that can result from various conditions

• two conditions

  • volume expansion → increase ECF

  • volume contraction → decrease ECF

• volumes after only in ECF or in both ECF & ICF

• also depend on osmolarity changes in ECF

volume & osmolarity changes principles

1. any changes in volume will first affect the ECF volume

2. the change in volume of ICF occurs only by changes in ECF osmolarity

3. at equilibrium (steady state), the ICF and ECF osmolarity will be the same

volume expansion

an increase in the extracellular fluid (ECF) volume often due to fluid retention or infused fluids

• 3 states

  • isosmotic

  • hyperosmotic

  • hyposmotic

isosmotic volume expansion

a type of body fluid disturbance characterized by an increase in extracellular fluid (ECF) volume without a change in ICF volume or ICF + ECF osmolarity

• no shift in water between ECF & ICF (↑ ECF + ↔ ICF vol + ↔ ECF & ICF osm)

• ↑ in BP

• examples

  • infusion of isotonic NaCl (0.9%)

  • gain of isotonic fluid

isosmotic volume expansion

isosmotic volume expansion (table)

hyperosmotic volume expansion

a type of body fluid disturbance characterized by an increase in extracellular fluid (ECF) volume with an increase in osmolarity

• water shift from ICF → ECF (↑ ECF vol + ↓ ICF vol + ↑ ECF & ICF osm)

• ↑ BP & ↑ alderstone (salt + H₂O)

• examples

  • infusion of hypertonic fluids

  • syndrome of inappropriate ADH (SIADH)

  • polydipsia

hyperosmotic volume expansion

hyperosmotic volume expansion (table)

hyposmotic volume expansion

a type of body fluid disturbance characterized by an increase in extracellular fluid (ECF) volume with a decrease in osmolarity

• water shift from ECF → ICF (↑ ECF & ICF vol + ↓ ECF & ICF osm)

• ↑ BP & ↑ ADH (only H₂O)

• examples

  • infusion of hypotonic fluids

  • ingesting dry NaCl (eating lots of salty foods)

  • Conn’s Syndrome

  • oat cell carcinoma of the lungs

hyposmotic volume expansion

hyposmotic volume expansion (table)

volume contraction

a decrease in extracellular fluid (ECF) volume resulting from water loss or solute gain

• 3 states

  • isosmotic

  • hyperosmotic

  • hyposmotic

isosmotic volume contraction

a type of body fluid disturbance characterized by a decrease in extracellular fluid (ECF) volume without a change in ICF volume or ICF + ECF osmolarity

• no shift in water between ECF & ICF (↓ ECF vol + ↔ ICF vol + ↔ ECF & ICF osm)

• ↓ in BP

• examples

  • loss of isotonic fluid

  • diarrhea (↑ Hct)

  • hemorrhage (↓ Hct)

  • severe vomiting

isosmotic volume contraction

isosmotic volume contraction - hemorrhage (table)

isosmotic volume contraction - diarrhea (table)

hyperosmotic volume contraction

a type of body fluid disturbance characterized by an decrease in extracellular fluid (ECF) volume with an increase in osmolarity

• water shift from ICF → ECF (↓ ECF & ICF vol + ↑ ECF & ICF osm)

• ↓ BP & ↓ ADH (only H₂O)

• examples

  • infusion of hypotonic fluids

  • diabetes insipidus

  • water deprivation

  • drinking alcohol

  • excessive sweating

  • fever

hyperosmotic volume contraction

hyperosmotic volume contraction (table)

hyposmotic volume contraction

a type of body fluid disturbance characterized by an decrease in extracellular fluid (ECF) volume with a decrease in osmolarity

• water shift from ECF → ICF (↓ ECF vol + ↑ ICF vol + ↓ ECF & ICF osm)

• ↓ BP & ↓ aldosterone (salt + H₂O)

• examples

  • infusion of hypertonic fluids

  • Addison’s disease

  • aldosterone deficiency

hyposmotic volume contraction

hyposmotic volume contraction (table)