Comprehensive Study Guide: Acid-Base Physiology, Henderson-Hasselbalch Kinetics, and Chemical Equation Balancing

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Acid-Base Physiology & Body Fluid pH

• Hydrogen Ion Concentration: Acid-base balance is the physiological mechanism maintaining hydrogen ion ($H^+$) concentration in body fluids within a strict range supporting cellular catalytic enzymes and physiological functions.

  • Acids: Dissociate in liquid to release hydrogen ions ($H^+$).

  • Bases: Dissociate into hydroxide ions ($OH^-$) or accept hydrogen ions.

  • Inverse Relationship: $pH$ varies inversely with $H^+$ ion concentration. A lower $pH$ indicates a higher concentration of $H^+$ ions.

• Normal Physiological Ranges:

  • Blood $pH$: $7.35\text{ to }7.45$ (Arterial baseline: $7.40$; $pH < 6.8$ or severe deviations lead to mortality).

  • Bicarbonate ($HCO_3^-$): $22\text{ to }26\,\text{mEq/L}$ (Baseline: $24\,\text{mEq/L}$; metabolic component regulated by the kidneys).

  • Partial Pressure of Arterial Carbon Dioxide ($PaCO_2$): $35\text{ to }45\,\text{mmHg}$ (Baseline: $40\,\text{mmHg}$; respiratory component regulated by the lungs).

Henderson-Hasselbalch Kinetics

• Mathematical Equation: $pH = 6.1 + \log\left(\frac{[HCO<em>3^-]}{0.03 \times PaCO</em>2}\right)$

  • $6.1$: Dissociation constant ($pK<em>a$) of carbonic acid ($H</em>2CO_3$).

  • $0.03$: Carbon dioxide solubility coefficient in human arterial blood plasma.

• Proportional Relationships:

  • Direct Variance: $pH$ directly varies with $HCO<em>3^-$ concentration. An increase in $HCO</em>3^-$ increases $pH$.

  • Inverse Variance: $pH$ inversely varies with $PaCO<em>2$. An increase in $PaCO</em>2$ decreases pH$.

  • Acid-Base Ratio: A normal plasma pH$of$7.40$corresponds to a$20:1$ratio of base ($HCO3^-$) to acid ($0.03 \times PaCO2).

• Acid-Base Disturbances & Compensation:

  • Respiratory Acidosis: High PaCO2$, low$pH$. Caused by hypoventilation. Kidneys compensate by retaining$HCO3^-$.</p></li><li><p><strong>Respiratory Alkalosis</strong>: Low$PaCO_2$, high$pH$. Caused by hyperventilation.</p></li><li><p><strong>Metabolic Acidosis</strong>: Low$HCO3^-$, low$pH$(e.g., Diabetic Ketoacidosis / DKA). Respiratory system compensates by hyperventilating to blow off excess$CO2$.</p></li><li><p><strong>Metabolic Alkalosis</strong>: High$HCO_3^-$, high$pH$.

Chemical Reactions & Equation Balancing

• Law of Conservation of Mass: Atoms are neither created nor destroyed in a chemical reaction; they are rearranged from reactants to products.

• Essential Biological Chemical Reactions:

  • Cellular Respiration: $C<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6CO<em>2 + 6H</em>2O + \text{ATP}$

  • Sodium Bicarbonate & Acetic Acid: $NaHCO<em>3 + CH</em>3COOH \rightarrow NaCH<em>3COO + H</em>2O + CO_2$

• Rules for Balancing Equations:

  1. Identify Atom Counts: Multiply coefficients by subscripts to determine total atoms per element on reactant and product sides.

  2. Adjust Coefficients: Change front coefficients to balance atom counts without modifying chemical subscripts.

  3. Examples:

  • Reaction of hydrogen and oxygen: $2H<em>2 + O</em>2 \rightarrow 2H_2O$

  • Reaction of sodium sulfide and silver iodide: $Na<em>2S + 2AgI \rightarrow Ag</em>2S + 2NaI$