Water, Acids, Bases, and Buffers

Vocabulary practice flashcards covering cellular environment, fluid compartments, water properties, electrolytes, osmolality, RAAS, acid-base chemistry, buffering systems, and pH disturbances.

Total Body Water (TBW)

The total volume of fluid in the body, making up approximately $60\%$ of body weight in a normal adult, distributed between intracellular and extracellular fluid compartments.

Intracellular Fluid (ICF)

The fluid compartment located inside body cells, comprising approximately two-thirds of total body water or about $40\%$ of total body weight.

Extracellular Fluid (ECF)

The fluid compartment located outside cells, comprising approximately one-third of total body water or about $20\%$ of body weight, divided into interstitial fluid ($10\,L$) and blood plasma ($5\,L$).

Transcellular Water

A small, specialized extracellular fluid volume contained within epithelial-lined body cavities, including cerebrospinal fluid, ocular fluid, and synovial fluid.

Hydrogen Bond

A weak noncovalent attraction between the partially positive hydrogen atom of one polar molecule (such as water) and the partially negative oxygen atom of an adjacent molecule.

Hydrophobic Effect

The thermodynamic exclusion of nonpolar, hydrophobic molecules (such as lipids) by water, which drives the self-assembly of cell membranes and protein folding.

$$\text{Na}^+/\text{K}^+\text{-ATPase}$$

An active transport membrane pump that hydrolyzes ATP to export $3\,\text{Na}^+$ ions out of the cell and import $2\,\text{K}^+$ ions into the cell, maintaining essential resting concentrations.

Digoxin

A cardiac glycoside that inhibits the $\text{Na}^+/\text{K}^+\text{-ATPase}$ pump, resulting in intracellular $\text{Na}^+$ accumulation, reduced $\text{Ca}^{2+}$ efflux, and enhanced force of cardiac contraction.

Anion Gap

A diagnostic calculation representing unmeasured anions in plasma, calculated as $\text{AG} = (\text{Na}^+ + \text{K}^+) - (\text{Cl}^- + \text{HCO}_3^-)$ with a normal reference range of $8\text{--}12\,\text{mEq/L}$.

Osmolality

The measure of solute concentration expressed as osmotically active particles per kilogram of solvent (mOsm/kg), with normal plasma osmolality ranging from $275$ to $295\,\text{mOsm/kg}$.

Osmotic Pressure

The minimum pressure required to prevent the movement of pure solvent across a semipermeable membrane into a solution containing solutes.

Renin-Angiotensin-Aldosterone System (RAAS)

A hormonal cascade initiated by decreased blood pressure or volume, wherein renal renin converts angiotensinogen to angiotensin I, ACE forms angiotensin II, and aldosterone secretion increases renal $\text{Na}^+$ and water reabsorption.

Conn's Syndrome

Primary hyperaldosteronism caused by autonomous adrenal overproduction of aldosterone, most commonly due to a single adrenal adenoma.

Volatile Acid

An acid generated by metabolism that can be converted to a gas and exhaled via the lungs, specifically carbon dioxide ($\text{CO}_2$).

Fixed Acid

A nonvolatile metabolic acid (such as lactic, sulfuric, or phosphoric acid) that cannot be eliminated by the lungs and must be excreted by the kidneys.

pH

The negative logarithm of hydrogen ion concentration, defined as $\text{pH} = -\log[\text{H}^+]$, maintaining a strict normal arterial range of $7.35\text{--}7.45$.

Acid Dissociation Constant ($K_a$)

An equilibrium constant quantifying acid strength, where a higher $K_a$ value indicates a stronger acid that dissociates more completely in water.

$$\text{p}K_a$$

The negative logarithm of the acid dissociation constant ($\text{p}K_a = -\log(K_a)$), representing the specific pH at which an acid is $50\%$ dissociated into equal parts HA and $\text{A}^-$.

Chemical Buffer System

A fast-acting mixture of a weak acid and its conjugate base that resists shifts in pH by binding or releasing $\text{H}^+$ ions immediately upon acid or base addition.

Bicarbonate Buffer System

The main extracellular buffer system in blood, governed by the reversible equation $\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{H}^+ + \text{HCO}_3^-$, regulated by lungs and kidneys.

Henderson-Hasselbalch Equation

A mathematical formula calculating pH from the $\text{p}K_a$ and ratio of conjugate base to weak acid: $\text{pH} = \text{p}K_a + \log\left(\frac{[\text{A}^-]}{[\text{HA}]}\right)$.

Chloride Shift

An exchange process in red blood cells where produced $\text{HCO}_3^-$ moves out into plasma in exchange for $\text{Cl}^-$ moving into the cell.

Phosphate Buffer System

A principal intracellular and renal tubular fluid buffer consisting of dihydrogen phosphate ($\text{H}_2\text{PO}_4^-$) and monohydrogen phosphate ($\text{HPO}_4^{2-}$).

Metabolic Acidosis

An acid-base disturbance defined by a primary drop in plasma bicarbonate ($\text{HCO}_3^- < 22\,\text{mEq/L}$) leading to an arterial pH below $7.35$.

Respiratory Acidosis

An acid-base disturbance caused by hypoventilation, defined by a primary increase in carbon dioxide partial pressure ($\text{pCO}_2 > 44\,\text{mmHg}$) and blood pH below $7.35$.

Metabolic Alkalosis

An acid-base disturbance defined by a primary rise in plasma bicarbonate ($\text{HCO}_3^- > 28\,\text{mEq/L}$) leading to an arterial pH above $7.45$.

Respiratory Alkalosis

An acid-base disturbance caused by hyperventilation, defined by a primary decrease in carbon dioxide partial pressure ($\text{pCO}_2 < 36\,\text{mmHg}$) and blood pH above $7.45$.

Potassium Shift in pH Abnormalities

The reciprocal exchange between $\text{H}^+$ and $\text{K}^+$ across cell membranes, where acidosis forces $\text{K}^+$ out of cells (causing hyperkalemia) and alkalosis drives $\text{K}^+$ into cells (causing hypokalemia).