Fluid, Electrolyte, and Acid–Base Balance

Vocabulary flashcards covering fluid compartments, electrolyte physiology, and acid–base balance.

Extracellular Fluid (ECF)

All body fluid outside cells—plasma, lymph, and cerebrospinal fluid; contains 99 % of water outside cells.

Intracellular Fluid (ICF)

Fluid within cells (cytosol/cytoplasm); its osmotic concentration normally matches that of ECF.

Cytosol

Gel-like intracellular fluid found only inside cells.

Cytoplasm

Cytosol plus all organelles contained within a cell.

Isotonic Solution

Fluid with the same solute concentration as a cell; no net water movement occurs.

Hypotonic Solution

Fluid with less solute and more water than a cell, causing the cell to swell.

Hypertonic Solution

Fluid with more solute and less water than a cell, causing the cell to shrink.

Osmosis

Passive movement of water across a membrane to equalize solute concentrations.

Electrolyte

Ion released by dissociation of inorganic compounds that can conduct electricity in solution (e.g., Na⁺, K⁺, Ca²⁺, Cl⁻, HCO₃⁻).

Electrolyte Balance

State in which electrolyte gains equal losses via sweat, absorption, and renal regulation.

Kidneys

Organs that secrete H⁺ into urine and generate bicarbonate buffers to regulate pH and electrolytes.

Lungs and pH Regulation

Eliminate CO₂; hyperventilation raises pH, hypoventilation lowers pH.

Sodium (Na⁺)

Dominant cation of ECF; major determinant of ECF osmolarity.

Sodium Chloride (NaCl)

Most common form of sodium in ECF; contributes to plasma osmolarity.

Sodium Bicarbonate (NaHCO₃)

ECF buffer that dissociates into Na⁺ and HCO₃⁻ to neutralize acids.

Hyponatremia

Abnormally low sodium level; often from excess water intake, heart failure, kidney disease, or diuretics.

Hypernatremia

Abnormally high sodium level; typically due to water deficit, high-salt diet, or improper IV fluids.

Potassium (K⁺)

Dominant cation of ICF; crucial for membrane potential.

Aldosterone

Hormone that increases renal potassium excretion and sodium reabsorption.

Hypokalemia

Abnormally low potassium concentration in the body.

Hyperkalemia

Abnormally high potassium concentration in the body.

Parathyroid Hormone (PTH)

Hormone that raises blood calcium levels; secreted by parathyroid glands.

Hypercalcemia

Excess calcium, often from malignancy, vitamin D excess, or hyperparathyroidism.

Hypocalcemia

Low calcium, commonly caused by hypoparathyroidism, chronic renal failure, or vitamin D deficiency.

Magnesium (Mg²⁺)

Essential cation involved in enzyme activity and neuromuscular function.

Hypomagnesemia

Abnormally low serum magnesium level.

Hypermagnesemia

Abnormally high serum magnesium level.

Phosphate Ions (PO₄³⁻)

Combine with calcium to form hydroxyapatite, strengthening bone and teeth.

Hydroxyapatite

Calcium phosphate mineral that gives hardness to bone and teeth.

Hypophosphatemia

Abnormally low phosphate level in blood.

Hyperphosphatemia

Abnormally high phosphate level in blood.

Chloride (Cl⁻)

Major anion of ECF, helping maintain osmotic pressure and acid-base balance.

Hypochloremia

Abnormally low chloride concentration.

Hyperchloremia

Abnormally high chloride concentration.

Strong Acid

Substance that completely dissociates in water, e.g., hydrochloric acid or sodium hydroxide (strong base).

Weak Acid/Base

Partially dissociates in water, e.g., acetic acid or ammonia.

Buffer

Substance that resists pH change by accepting or donating H⁺ ions.

Carbonic Acid–Bicarbonate Buffer System

Primary blood buffer involving H₂CO₃ and HCO₃⁻ regulating extracellular pH.

Protein Buffer

Intracellular and plasma proteins whose amino acids can accept or release H⁺.

Acidosis

Physiological state in which plasma pH is below 7.35.

Metabolic Acidosis

Low pH due to renal failure, diabetic ketoacidosis, or lactic acidosis.

Respiratory Acidosis

Low pH from CO₂ retention, e.g., COPD or drug-induced respiratory depression.

Alkalosis

Physiological state in which plasma pH exceeds 7.45.

Metabolic Alkalosis

High pH caused by vomiting or diuretic abuse.

Respiratory Alkalosis

High pH from excessive CO₂ loss, often due to anxiety or pregnancy.

Combined Respiratory and Metabolic Acidosis

Simultaneous respiratory and metabolic pH disturbances seen in critically ill patients (e.g., COPD with renal failure or DKA).