Chapter 22: Fluid, Electrolyte, and Acid–Base Balance

Comprehensive vocabulary flashcards covering fluid compartments, water homeostasis, electrolyte functions and imbalances, and acid-base regulation mechanisms from Chapter 22.

Intracellular Fluid (ICF)

The fluid located inside cells (also called cytosol), accounting for about two-thirds ($67\%$) of total body fluid.

Extracellular Fluid (ECF)

Body fluid outside cells, accounting for about one-third ($33\%$) of total body fluid, consisting primarily of interstitial fluid and blood plasma.

Interstitial Fluid

The portion of extracellular fluid (about $80\%$ of ECF) that occupies the spaces between tissue cells, including lymph, CSF, synovial fluid, humors of the eye, and serous fluids.

Fluid Balance

The condition in which the various body fluid compartments contain the normal and required volume of water and concentrations of solutes.

Electrolyte

An inorganic substance that dissociates into ions in solution, functioning to control osmosis, maintain acid–base balance, carry electrical current, and serve as enzyme cofactors.

Metabolic Water

Water produced in the body as a byproduct of metabolic reactions, contributing approximately $200\,\text{mL}$ per day to total body water gain.

Dehydration

A state in which water loss is greater than water gain, resulting in a decrease in body fluid volume and an increase in the osmotic pressure of body fluids.

Thirst Center

An area located in the hypothalamus that governs the urge to drink when stimulated by osmoreceptors, dry mouth and pharynx, or angiotensin II.

Aldosterone

An adrenal hormone that promotes renal reabsorption of $\text{Na}^+$ and $\text{Cl}^-$, leading to increased water reabsorption via osmosis and reduced water loss in urine.

Atrial Natriuretic Peptide (ANP)

A cardiac hormone released in response to atrial stretching that promotes natriuresis, increasing the excretion of $\text{Na}^+$ and water to lower blood volume.

Antidiuretic Hormone (ADH)

The major hormone regulating water loss, which promotes the insertion of water-channel proteins into collecting duct membranes to increase water permeability and reabsorption.

Natriuresis

The elevated urinary excretion of sodium ($\text{Na}^+$) and chloride ($\text{Cl}^-$) accompanied by the osmotic loss of water.

Sodium ($\text{Na}^+$)

The most abundant cation in extracellular fluid (normal adult plasma range: $136\text{--}148\,\text{mEq/liter}$), critical for action potentials, muscle contraction, and fluid balance.

Chloride ($\text{Cl}^-$)

The major extracellular anion (normal adult plasma range: $95\text{--}105\,\text{mEq/liter}$), which plays a key role in regulating osmotic pressure and forming $\text{HCl}$ in gastric juice.

Potassium ($\text{K}^+$)

The most abundant intracellular cation (normal adult plasma range: $3.5\text{--}5.0\,\text{mEq/liter}$), essential for establishing the resting membrane potential and contributing to pH regulation.

Calcium ($\text{Ca}^{2+}$)

The most abundant mineral in the body; an extracellular cation functioning in blood clotting, neurotransmitter release, muscle contraction, and bone and tooth structure.

Hyponatremia

A condition characterized by a blood sodium level below $136\,\text{mEq/liter}$, presenting with muscular weakness, dizziness, hypotension, tachycardia, mental confusion, and coma.

Hypernatremia

A condition characterized by a blood sodium level above $148\,\text{mEq/liter}$, causing ECF hypertonicity and cellular dehydration, marked by intense thirst, hypertension, and convulsions.

Hypokalemia

A condition where plasma potassium levels fall below $3.5\,\text{mEq/liter}$, causing muscle fatigue, flaccid paralysis, mental confusion, and flattening of the T wave on an electrocardiogram.

Hyperkalemia

A condition where plasma potassium levels exceed $5.0\,\text{mEq/liter}$, resulting in irritability, nausea, diarrhea, muscular weakness, and possible death via ventricular fibrillation.

Hypocalcemia

A blood calcium deficiency (ionized below $4.5\,\text{mEq/liter}$), characterized by numbness, hyperactive reflexes, tetany, muscle cramps, and dangerous laryngeal spasms.

Hypercalcemia

An abnormally high plasma calcium level (ionized above $5.5\,\text{mEq/liter}$), causing lethargy, weakness, polyuria, bone pain, anorexia, confusion, stupor, and coma.

Buffer Systems

Chemical substances that act rapidly to temporarily bind excess $\text{H}^+$, converting strong acids and bases into weak ones to minimize drastic shifts in body fluid pH.

Protein Buffer System

The most abundant buffer system in body cells and blood, which relies on hemoglobin in red blood cell cytosol and albumin in blood plasma.

Carbonic Acid–Bicarbonate Buffer System

A major regulator of blood pH and the most abundant buffer system in extracellular fluid, utilizing carbonic acid ($\text{H}_2\text{CO}_3$) and bicarbonate ions ($\text{HCO}_3^-$).

Acidosis

A clinical condition where systemic arterial blood pH drops below $7.35$, with the principal physiological effect being depression of the central nervous system.

Alkalosis

A clinical condition where systemic arterial blood pH rises above $7.45$, with the principal physiological effect being overexcitability of the central nervous system.