Chapter 26 – Water, Electrolyte, and Acid-Base Balance

Vocabulary flashcards covering key terms and definitions from Chapter 26 on water, electrolyte, and acid–base balance.

Body Fluids

All water contained in the body; ~50 % of adult weight, 75 % in infants.

Intracellular Fluid (ICF)

Fluid located inside cells; ~40 % of body weight or two-thirds of total body water.

Extracellular Fluid (ECF)

Fluid outside cells; ~20 % of body weight, includes plasma, interstitial, and transcellular fluids.

Plasma

Liquid portion of blood found inside blood vessels; part of ECF.

Interstitial Fluid

Fluid that bathes and surrounds tissue cells; major component of ECF.

Transcellular Fluid

Specialized fluids in body cavities (CSF, pleural, synovial, etc.); ~1 % of total body water.

Total Body Water (TBW)

Sum of water in all compartments; TBW ≈ 0.6 × body weight (≈42 L in 70 kg male).

Osmolality

Concentration of dissolved particles in a solution; normal body fluids 285–300 mOsm/kg.

Thirst Center

Region in hypothalamus that initiates desire to drink when stimulated by osmo- or baroreceptors.

Osmoreceptors

Hypothalamic receptors that detect ECF osmolality changes to regulate thirst and ADH release.

Baroreceptors

Pressure receptors (carotid sinus, aortic arch, atria) that detect blood volume/pressure changes.

Juxtaglomerular Apparatus

Kidney structure that releases renin when renal perfusion pressure drops.

Antidiuretic Hormone (ADH)

Posterior pituitary hormone that increases water reabsorption in distal tubule and collecting duct.

Aldosterone

Adrenal cortical hormone that increases Na⁺ (and water) reabsorption and K⁺ excretion in kidneys.

Renin-Angiotensin-Aldosterone System (RAA)

Hormonal cascade (renin → angiotensin II → aldosterone) that raises blood volume and pressure.

Atrial Natriuretic Hormone (ANH)

Peptide from atrial muscle that promotes Na⁺/water excretion, lowering blood volume and pressure.

Dehydration

Loss of body water causing increased osmolality, reduced saliva, lower blood volume, triggering thirst.

Hyponatremia

Low plasma Na⁺ concentration; causes lethargy, confusion, seizures, coma.

Hypernatremia

High plasma Na⁺ concentration; causes thirst, fever, convulsions, pulmonary edema.

Potassium Homeostasis

Balance of K⁺ maintained mainly by aldosterone-regulated renal secretion.

Calcium Homeostasis

Regulation of blood Ca²⁺ by parathyroid hormone (raises Ca²⁺) and calcitonin (lowers Ca²⁺).

Parathyroid Hormone (PTH)

Hormone that increases blood Ca²⁺ by stimulating bone resorption and kidney Ca²⁺ reabsorption.

Calcitonin

Thyroid hormone that lowers blood Ca²⁺ by promoting bone Ca²⁺ deposition.

Buffer

Substance that resists pH change by binding or releasing H⁺ ions.

Carbonic Acid/Bicarbonate Buffer

Primary extracellular buffer pairing H₂CO₃ with HCO₃⁻ to neutralize acids or bases.

Protein Buffer System

Intracellular and plasma proteins (e.g., hemoglobin) that accept or donate H⁺ ions.

Phosphate Buffer System

Intracellular and renal buffer using H₂PO₄⁻/HPO₄²⁻ to moderate pH.

Acid-Base Balance

Maintenance of blood pH (7.35–7.45) via buffers, respiration, and renal function.

Electrolytes

Charged ions (Na⁺, K⁺, Cl⁻, Ca²⁺) critical for fluid balance, nerve conduction, and muscle function.

Water Follows Sodium

Physiologic principle that water movement is largely driven by Na⁺ reabsorption or loss.