Fluid and Electrolyte Balance in the Human Body

Comprehensive vocabulary flashcards covering fluid types, transport mechanisms, and electrolyte imbalances based on the lecture notes.

Molecule

Two or more atoms chemically bonded together.

Ion

An atom or molecule with an electrical charge.

Cation

A positively charged ion (e.g., $Na^+$, $K^+$).

Anion

A negatively charged ion (e.g., $Cl^-$, $HCO_3^-$).

Electrolyte

A substance (e.g., $NaCl$) that dissolves in water to form ions.

Electrolyte concentration

Commonly expressed as milliequivalents per liter ($mEq/L$).

mEq vs. mOsm for monovalent ions

$1\,mEq = 1\,mOsm$.

mEq vs. mOsm for divalent ions

$1\,mEq = 1/2\,mOsm$.

Total body fluid volume

Approximately $60\%$ of adult body weight; loss of $20\%$ is life-threatening.

ICF (Intracellular fluid)

$2/3$ of body fluid with major cation $K^+$ and major anion $PO_4^{3-}$.

ECF (Extracellular fluid)

$1/3$ of body fluid with major cation $Na^+$ and major anion $Cl^-$.

Diffusion

Solutes move from high to low concentration without energy input.

Osmosis

Water moves from low solute concentration to high to dilute the higher concentration without energy input.

Hydrostatic pressure

Pressure that pushes fluid out of blood vessels.

Oncotic pressure

Pressure from proteins like albumin that pulls fluid into vessels.

Active Transport

Solutes move from low to high concentration, requiring energy in the form of $ATP$.

Sodium-potassium pump

Moves $Na^+$ out of cells and $K^+$ into cells to maintain cell function.

Osmolality

Number of dissolved particles per kilogram of water.

Normal plasma osmolality

$280-294\,mOsm/kg$.

Tonicity

Describes how a solution affects cell volume based on its osmolality.

Isotonic

Same osmolality as plasma; no net water movement (e.g., $0.9\%\,NaCl$, $D5W$, or Lactated Ringer's solution).

Hypotonic

Lower osmolality than plasma; water moves into cells making them swell (e.g., $0.45\%\,NaCl$).

Hypertonic

Higher osmolality than plasma; water moves out of cells making them shrink (e.g., $3\%\,NaCl$ or $10\%$ dextrose in water).

Sensible losses

Measurable fluid losses such as urine, sweat, and feces.

Insensible losses

Not measurable fluid losses such as water vapor from breathing and evaporation from skin.

Average daily urine output

$\sim 1500\,mL$.

Hypervolemia

Fluid volume excess caused by excess intake of sodium and water; signs include rapid weight gain, bounding pulse, and peripheral or pulmonary edema.

SIADH

Too much $ADH$ leading to water retention and hyponatremia.

Diabetes insipidus

Too little $ADH$ leading to excess water loss.

Oliguria

$< 30\,mL/hour$ or $< 400\,mL/day$.

Urine specific gravity indicating dehydration

$> 1.030$.

H+ and K+ exchange

Acidosis causes $K^+$ to shift out of cells, raising blood potassium levels.

Hyponatremia

Serum sodium $< 135\,mEq/L$; causes water to shift from ECF to ICF resulting in cellular swelling (especially brain cells).

Hypernatremia

Serum sodium $> 145\,mEq/L$; increased osmolality causes water to shift from ICF to ECF, making cells shrink.

Hypokalemia

Serum potassium level $< 3.5\,mEq/L$; symptoms include anorexia, ECG changes, hypotension, and risk of cardiac or respiratory arrest.

Hyperkalemia

Serum potassium level $> 5.0\,mEq/L$; etiologies include kidney injury, metabolic acidosis, and tissue breakdown.

Kayexalate

Medication administered for hyperkalemia that promotes $K^+$ excretion through the GI tract.

Hypocalcemia

Serum Calcium $< 8.5\,mg/dL$; symptoms occur specifically when ionized calcium is low.

Trousseau's sign

A carpopedal spasm caused by inflating a blood pressure cuff; indicates hypocalcemia.

Chvostek's sign

Twitching of facial muscles upon tapping; indicates hypocalcemia.

Hypercalcemia

Serum calcium $> 10.5\,mg/dL$; can lead to nephrolithiasis (kidney stones).

Hypomagnesemia

Serum magnesium $< 1.5\,mEq/L$; associated with nystagmus (involuntary eye movement).

Hypermagnesemia

Serum magnesium $> 2.3\,mEq/L$.

Hypophosphatemia

Serum phosphate $< 2.5\,mg/dL$; symptoms include tremors, ataxia, and muscle weakness.

Hyperphosphatemia

Serum phosphate $> 4.5\,mg/dL$ (or $> 2.9\,mEq/L$); can lead to calcium-phosphate deposits in kidneys.