Biochemistry Foundations for Anatomy & Physiology: Water, Salts, Acids, and Bases

Biochemistry in Anatomy & Physiology

Introduction to Biochemistry

Biochemistry is the study of the chemical composition and reactions of living matter. Understanding biochemistry is essential for comprehending the structure and function of the human body at the molecular level. Chemicals in the body are classified as either organic or inorganic compounds.

• Inorganic compounds: Include water, salts, and many acids and bases. These compounds generally do not contain carbon.

• Organic compounds: Include carbohydrates, fats, proteins, and nucleic acids. These compounds contain carbon, are usually large, and are covalently bonded.

Both types of compounds are equally essential for life.

Inorganic Compounds

Water: The Most Abundant Inorganic Compound

Water is the most abundant inorganic compound in living cells, accounting for 60%–80% of their volume. Its unique properties make it vital for life.

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

• High heat of vaporization: Evaporation of water requires significant energy, making sweating an effective cooling mechanism.

• Polar solvent properties: Water dissolves and dissociates ionic substances, forming hydration layers around large charged molecules (e.g., proteins). It is the body's major transport medium.

• Reactivity: Water is involved in many chemical reactions, including hydrolysis and dehydration synthesis.

Salts

Salts are ionic compounds that dissociate in water, separating into cations (positively charged ions) and anions (negatively charged ions), except for H+ and OH- ions.

• All ions are called electrolytes because they conduct electrical currents in solution.

• Ions such as sodium (Na+), potassium (K+), calcium (Ca2+), and iron (Fe2+/3+) play specialized roles in body functions.

• Ionic balance is vital for homeostasis.

• Common salts in the body include NaCl (sodium chloride), CaCO3 (calcium carbonate), and KCl (potassium chloride).

Acids and Bases

Definitions and Properties

• Acids: Proton donors that release hydrogen ions (H+) in solution. Example: $\mathrm{HCl} \rightarrow \mathrm{H}^+ + \mathrm{Cl}^-$

• Important acids: Hydrochloric acid (HCl), acetic acid (HC2H3O2), and carbonic acid (H2CO3).

• Bases: Proton acceptors that pick up H+ ions in solution. Example: $\mathrm{NaOH} \rightarrow \mathrm{Na}^+ + \mathrm{OH}^-$

• When a base dissolves in solution, it releases a hydroxyl ion (OH-).

• Important bases: Bicarbonate ion (HCO3-) and ammonia (NH3).

Acid-Base Concentration and the pH Scale

The pH scale measures the concentration of hydrogen ions [H+] in a solution. The more hydrogen ions, the more acidic the solution. The pH is the negative logarithm of [H+] in moles per liter, ranging from 0 to 14.

• The pH scale is logarithmic: each pH unit represents a tenfold difference in [H+].

• Example: A pH 5 solution is 10 times more acidic than a pH 6 solution.

Classification of Solutions by pH

• Acidic solutions: High [H+], low pH (0–6.99).

• Neutral solutions: Equal numbers of H+ and OH- ions. Pure water is neutral with pH 7: $[\mathrm{H}^+] = 10^{-7} \ \mathrm{M}$.

• Alkaline (basic) solutions: Low [H+], high pH (7.01–14).

pH Range	Type of Solution	[H+] Relative to Neutral
0–6.99	Acidic	Higher
7	Neutral	Equal to pure water
7.01–14	Alkaline (Basic)	Lower

Example: Blood has a slightly basic pH of about 7.4, which is tightly regulated for proper physiological function.

Additional info: The regulation of acids and bases in the body is crucial for maintaining homeostasis, as even small deviations in pH can disrupt cellular processes and enzyme activity.