Fundamentals of Chemistry in Anatomy & Physiology: Organic, Inorganic Compounds, Water, Acids, Bases, and pH

Basic Chemistry in Anatomy & Physiology

Introduction to Chemistry in Living Systems

Chemistry is essential for understanding the composition and reactions of living matter. In anatomy and physiology, chemical principles explain how biological molecules interact and function within the body.

• Organic compounds contain carbon and include carbohydrates, lipids, proteins, and nucleic acids.

• Inorganic compounds include water, salts, and many acids and bases; most do not contain carbon.

• Organic compounds are usually large and covalently bonded, and are essential for life.

Inorganic Compounds

Water: The Most Important Inorganic Compound

Water makes up 60–80% of the volume of living cells and is vital due to its unique properties.

• High heat capacity: Water can absorb and release large amounts of heat with little temperature change, helping to stabilize body temperature.

• High heat of vaporization: Evaporation of water requires significant energy, which is important for cooling mechanisms such as sweating.

• Polar solvent properties: Water dissolves ionic substances and forms hydration layers around large charged molecules (e.g., proteins), making it an excellent transport medium.

• Reactivity: Water is involved in hydrolysis and dehydration synthesis reactions, which are essential for building and breaking down biological molecules.

• Cushioning: Water protects organs from physical trauma; for example, cerebrospinal fluid cushions nervous system organs.

Properties of Water

Thermal and Solvent Properties

Water's thermal properties help maintain homeostasis, while its solvent abilities facilitate biochemical reactions.

• High heat capacity: Water resists sudden changes in temperature.

• High heat of vaporization: Large amounts of heat are needed to evaporate water.

• Polar solvent properties: Water dissociates ionic substances and forms hydration layers around charged molecules.

• Reactivity: Water is a reactant in hydrolysis and dehydration synthesis reactions.

• Cushioning: Water protects organs from trauma.

Salts, Acids, and Bases

Salts

Salts are ionic compounds that dissociate in water to form electrolytes, which are essential for electrical signaling and homeostasis.

• Electrolytes: Substances that conduct electrical currents in solution due to the presence of ions.

• Common body salts include sodium chloride (NaCl), potassium chloride (KCl), and calcium phosphates.

• Electrolytes play specialized roles in body functions, such as nerve impulse transmission and muscle contraction.

Acids

Acids are substances that release hydrogen ions (H+) in solution and are classified as proton donors.

• Electrolytes: Acids dissociate in water to release ions.

• Proton donors: Acids release H+ (protons) in solution.

• Examples: Hydrochloric acid (HCl), acetic acid (HC2H3O2), carbonic acid (H2CO3).

Bases

Bases are substances that accept hydrogen ions (H+) and release hydroxyl ions (OH-) in solution.

• Proton acceptors: Bases pick up H+ ions.

• When dissolved, bases release OH- ions.

• Examples: Bicarbonate ion (HCO3-), ammonia (NH3).

Acids and Bases: pH

pH Scale and Measurement

The pH scale measures the concentration of hydrogen ions in a solution, indicating its acidity or alkalinity.

• pH definition: pH is the negative logarithm of the hydrogen ion concentration in moles per liter.

• Formula: $pH = -\log[H^+]$

• The pH scale ranges from 0 (most acidic) to 14 (most basic).

• Each pH unit represents a tenfold difference in hydrogen ion concentration.

• Body fluids operate within a narrow pH range for proper physiological function.

Acids, Bases, and Neutralization

Acids and bases can neutralize each other, forming water and a salt.

• Neutralization reaction: When an acid and a base are mixed, they react to form water and a salt.

• Example equation: $\text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O}$

Buffers

Buffers are systems that resist changes in pH by absorbing or releasing hydrogen ions.

• Composed of a weak acid and a weak base.

• Buffers prevent large swings in pH, maintaining homeostasis.

• Example: The bicarbonate buffer system in blood.

Summary Table: Properties of Water, Acids, and Bases

Property	Water	Acids	Bases
Definition	Polar molecule, universal solvent	Proton donor, releases H+	Proton acceptor, releases OH-
Role in Body	Transport, temperature regulation, cushioning	Digestion, metabolism	Neutralization, pH balance
Examples	H2O	HCl, HC2H3O2, H2CO3	NaOH, HCO3-, NH3

Key Terms and Definitions

• Organic compound: Molecule containing carbon, typically large and covalently bonded.

• Inorganic compound: Molecule not containing carbon (except CO2 and CO), includes water, salts, acids, and bases.

• Electrolyte: Substance that conducts electricity when dissolved in water due to ion formation.

• Buffer: System that resists changes in pH.

• pH: Measure of hydrogen ion concentration; scale from 0 (acidic) to 14 (basic).

Example Applications

• Body temperature regulation: Water's high heat capacity helps maintain stable internal temperatures.

• Blood pH regulation: Buffers such as the bicarbonate system maintain blood pH within a narrow range.

• Electrolyte balance: Sodium, potassium, and calcium ions are vital for nerve and muscle function.

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard anatomy and physiology textbooks.