CH 8 - Fluid and Electrolyte Balance

Vocabulary flashcards covering key terms, hormones, processes, and electrolyte values related to fluid and electrolyte balance.

Intracellular Fluid (ICF)

Fluid located inside the body’s cells; accounts for about 40 % of total body weight.

Extracellular Fluid (ECF)

All body fluid outside the cells (interstitial, intravascular, transcellular); roughly 20 % of body weight.

Interstitial Fluid

Fluid found in the spaces between cells within tissues.

Intravascular Fluid

Fluid contained within blood vessels (the plasma portion of blood).

Transcellular Fluid

Small specialized fluid volumes in body cavities (e.g., cerebrospinal, pleural, synovial); formerly called the “third space.”

Osmosis

Passive movement of water across a semipermeable membrane from an area of higher water concentration to lower concentration.

Osmotic Pressure

The pulling force generated by osmosis that draws water toward higher solute concentration.

Hydrostatic Force

The pushing pressure exerted by fluid in an extracellular compartment that drives water outward.

Tonicity

Comparative osmotic pressure of two solutions separated by a semipermeable membrane.

Isotonic Solution

Has equal solute concentration to body fluids; causes no net fluid shift across cell membranes.

Hypotonic Solution

Lower solute concentration than body fluids; water moves into cells causing them to swell.

Hypertonic Solution

Higher solute concentration than body fluids; water moves out of cells causing them to shrink.

Antidiuretic Hormone (ADH)

Hormone released during hypovolemia that promotes water reabsorption in kidneys to raise blood pressure.

Aldosterone

Adrenal cortex hormone stimulated by hypovolemia that increases renal reabsorption of sodium and water.

Renin–Angiotensin–Aldosterone System (RAAS)

Hormonal cascade triggered by hypotension; renin → angiotensin I → angiotensin II → vasoconstriction & aldosterone release to increase BP and blood volume.

Edema

Excess fluid accumulation in the interstitial space.

Anasarca

Severe, generalized, body-wide edema.

Hypervolemia (Fluid Volume Excess)

Excess fluid in the intravascular compartment, often from high sodium or water intake.

Water Intoxication

Excessive water in the intracellular compartment that can rupture cells and be fatal.

Fluid Deficit (Hypovolemia)

Insufficient intravascular fluid volume leading to increased blood solutes and potential hypotension.

Cation

An ion carrying a positive electrical charge.

Anion

An ion carrying a negative electrical charge.

Sodium (Na⁺)

Major ECF cation; controls serum osmolality and water balance; think neurologic issues when abnormal.

Chloride (Cl⁻)

Major ECF anion; pairs with sodium to maintain fluid and acid–base balance; abundant in CSF.

Potassium (K⁺)

Principal ICF cation; crucial for electrical conduction in heart, nerves, and muscles; imbalances cause arrhythmias.

Calcium (Ca²⁺)

Mostly in bones/teeth; needed for nerve transmission and muscle contraction; imbalances produce muscle symptoms.

Magnesium (Mg²⁺)

ICF cation stored in bone/muscle; supports neuromuscular function, cardiac rhythm, BP, glucose control; direct with Ca²⁺, inverse with P.

Phosphorus (P)

Mainly stored in bones; inverse relationship with calcium; shares similar manifestations with calcium disorders.

Electrolyte Normal Ranges

Na⁺ 135-145 mEq/L | Cl⁻ 98-108 mEq/L | Mg²⁺ 1.8-2.4 mEq/L | Ca²⁺ 8.6-10.2 mg/dL | K⁺ 3.5-5 mEq/L | P 2.5-4.5 mg/dL