Biochemistry in Anatomy & Physiology: Inorganic Compounds, Acids, Bases, and Water 2B

Biochemistry in Anatomy & Physiology

Introduction to Biochemistry

Biochemistry is the study of the chemical composition and reactions of living matter. In the context of anatomy and physiology, understanding biochemistry is essential for comprehending how the body functions at a molecular level. Chemicals in the body are classified as either organic or inorganic compounds, both of which are vital for life.

• 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.

Inorganic Compounds

Water: Properties and Importance

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

• 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, providing an effective cooling mechanism (e.g., sweating).

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

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

• Cushioning: Water protects organs from physical trauma (e.g., cerebrospinal fluid cushions the brain and spinal cord).

Dissociation of Salt in Water

When salts dissolve in water, they dissociate into their component ions. For example, sodium chloride (NaCl) dissociates into sodium (Na+) and chloride (Cl−) ions. The polar nature of water molecules facilitates this process by surrounding and stabilizing the ions.

Salts and Electrolytes

Salts are ionic compounds that dissociate into separate ions in water. These ions are classified as:

• Cations: Positively charged ions (e.g., Na+, K+, Ca2+, Fe2+/3+).

• Anions: Negatively charged ions (e.g., Cl−, PO43−).

All ions in solution are called electrolytes because they can conduct electrical currents. Electrolytes are essential for nerve impulse transmission, muscle contraction, and maintaining fluid balance.

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

Acids and Bases

Definitions and Properties

• Acids: Substances that release hydrogen ions (H+) in solution; they are proton donors. For example, hydrochloric acid (HCl) dissociates as follows: $\mathrm{HCl} \rightarrow \mathrm{H}^+ + \mathrm{Cl}^-$

• Bases: Substances that accept hydrogen ions; they are proton acceptors. When a base dissolves in water, it releases hydroxyl ions (OH−). For example, sodium hydroxide (NaOH) dissociates as follows: $\mathrm{NaOH} \rightarrow \mathrm{Na}^+ + \mathrm{OH}^-$

Important acids in the body include hydrochloric acid (HCl), acetic acid (HC2H3O2), and carbonic acid (H2CO3). Important bases include bicarbonate ion (HCO3−) and ammonia (NH3).

Electrolytes and Homeostasis

Both acids and bases are electrolytes because they ionize and dissociate in water. The balance of acids and bases (pH balance) is crucial for maintaining homeostasis in the body.

Summary Table: Key Inorganic Compounds and Their Roles

Compound	Type	Main Role in the Body
Water (H2O)	Inorganic	Solvent, temperature regulation, chemical reactions, cushioning
Sodium chloride (NaCl)	Salt	Electrolyte balance, nerve impulse transmission
Hydrochloric acid (HCl)	Acid	Stomach acid, digestion
Bicarbonate (HCO3−)	Base	Buffering of blood pH
Calcium phosphate	Salt	Bone and teeth structure

Key Terms

• Biochemistry: The study of chemical processes in living organisms.

• Inorganic compound: A compound that generally does not contain carbon.

• Electrolyte: A substance that conducts electricity when dissolved in water.

• Acid: A proton donor; releases H+ in solution.

• Base: A proton acceptor; releases OH− in solution.

• Salt: An ionic compound formed from the neutralization of an acid and a base.

Additional info: The pH scale, buffer systems, and the physiological importance of acid-base balance are also critical topics in biochemistry and will be covered in further detail in subsequent sections or chapters.