Water, pH, Buffers & Acid-Base Balance – Vocabulary

A set of vocabulary flashcards covering key terms from the lecture on water chemistry, buffers, and acid–base balance.

Homeostasis

The maintenance of a constant internal environment, including stable H⁺ concentration and body-water content.

Total Body Water

All water contained in the body; ≈50–60 % of adult weight, 75 % in children.

Intracellular Fluid (ICF)

Fluid contained within cells; about 60 % of total body water.

Extracellular Fluid (ECF)

Fluid outside cells (plasma + interstitial fluid); about 40 % of total body water.

Plasma

The liquid portion of blood after removal of cells; part of the ECF.

Interstitial Fluid

Fluid in tissue spaces between cells; part of the ECF.

Osmolality

Total concentration of dissolved particles in a kilogram of water, expressed in mOsm/kg.

Semipermeable Membrane

Biological barrier that allows free water movement but restricts solute passage.

Osmotic Pressure

Pressure required to prevent water movement across a semipermeable membrane.

Dehydration

Condition in which extracellular osmolality is high, causing water to leave cells.

Hyperglycemia

Elevated blood glucose that raises plasma osmolality, pulling water out of cells.

Dipole (Water)

Molecule with partial positive (H) and negative (O) charges, enabling hydrogen bonding.

Hydrogen Bond

Weak attraction between a hydrogen atom and an electronegative atom (O or N).

pH

Negative log₁₀ of the hydrogen-ion concentration; measures acidity or basicity.

Acid

Compound that donates H⁺ (proton donor).

Base

Compound that accepts H⁺ (proton acceptor).

Strong Acid

Acid that dissociates completely in water (e.g., HCl, H₂SO₄).

Weak Acid

Acid that only partially dissociates in water (e.g., acetoacetic acid).

Dissociation Constant (Ka)

Equilibrium constant for acid dissociation; indicates acid strength.

pKa

Negative log of Ka; lower pKa = stronger acid.

Henderson-Hasselbalch Equation

Relates pH, pKa and ratio of conjugate base to weak acid (pH = pKa + log[A⁻]/[HA]).

Buffer

Mixture of weak acid and its conjugate base that resists pH change.

Buffering Capacity

Ability of a buffer to resist pH change; maximal when pH ≈ pKa.

Buffer Region

pH range within ±1 unit of a buffer’s pKa where it is most effective.

Bicarbonate Buffer System

Major ECF buffer comprising carbonic acid (H₂CO₃) and bicarbonate (HCO₃⁻).

Carbonic Anhydrase

Enzyme that rapidly converts CO₂ + H₂O ⇌ H₂CO₃.

Hemoglobin Buffer

Buffering by histidine residues of hemoglobin in red cells.

Phosphate Buffer System

Intracellular/renal buffer pair H₂PO₄⁻ / HPO₄²⁻ (pKa 6.8).

Ammonia Buffer

Renal buffer using NH₃/NH₄⁺ to excrete H⁺ in urine.

Volatile Acid

Carbonic acid generated from CO₂; excreted via lungs.

Nonvolatile Acid

Fixed acids (lactic, ketone, sulfuric, phosphoric) excreted by kidneys.

Metabolic Acidosis

Primary decrease in HCO₃⁻ or excess H⁺ leading to low pH.

Metabolic Alkalosis

Primary increase in HCO₃⁻ or loss of H⁺ causing high pH.

Respiratory Acidosis

Elevated PCO₂ from hypoventilation, lowering pH.

Respiratory Alkalosis

Decreased PCO₂ from hyperventilation, raising pH.

Compensation

Physiologic response that adjusts PCO₂ or HCO₃⁻ to limit pH change.

Acidemia

Arterial blood pH < 7.35.

Alkalemia

Arterial blood pH > 7.45.

Arterial Blood Gas (ABG)

Laboratory test measuring pH, PCO₂ and HCO₃⁻ to assess acid-base status.

PCO₂

Partial pressure of dissolved CO₂ in blood; respiratory component of acid-base balance.

HCO₃⁻

Bicarbonate ion; metabolic component of acid-base balance.

Kussmaul Respiration

Deep, rapid breathing seen in metabolic acidosis to lower PCO₂.

Hyperventilation

Increased ventilation causing decreased PCO₂ (respiratory alkalosis).

Hypoventilation

Reduced ventilation causing elevated PCO₂ (respiratory acidosis).

Ionizable Side Chain

Amino-acid group that can gain or lose H⁺, affecting protein charge.

Protein Denaturation

Loss of protein structure and function due to extreme pH or other factors.

Bicarbonate Reclamation

Renal reabsorption of filtered HCO₃⁻ to prevent its loss.

Bicarbonate Generation

Renal production of new HCO₃⁻ accompanied by H⁺ excretion.

Ketone Bodies

Acetoacetic and 3-hydroxybutyric acids produced in fatty-acid oxidation; weak acids.

Lactic Acid

Product of anaerobic glycolysis; contributes to metabolic acidosis.

Sulfuric Acid

Strong acid formed from sulfur-containing amino acid metabolism.

Phosphoric Acid

Acid produced from phospholipid metabolism; nonvolatile.

Milliequivalent (mEq)

Unit representing one millimole of charge, used for acid/base quantities.

Milliosmole (mOsm)

Unit expressing number of osmotically active particles per kilogram of water.

Histidine Residue

Amino-acid side chain in proteins (e.g., hemoglobin) that contributes to buffering.

Base:Acid Ratio (20 : 1)

Physiological HCO₃⁻ : H₂CO₃ ratio in blood at pH 7.4.