Chapter 2: Basic Chemistry for Anatomy and Physiology

Chapter 2: Basic Chemistry

2.1 Basic Atomic Structure

This section introduces the fundamental building blocks of matter and their relevance to anatomy and physiology.

• Atom: The smallest unit of an element that retains the properties of that element. Atoms consist of a nucleus (containing protons and neutrons) and electrons orbiting the nucleus.

• Proton: A positively charged particle found in the nucleus of an atom.

• Neutron: An uncharged particle found in the nucleus of an atom.

• Electron: A negatively charged particle that orbits the nucleus in electron shells.

• Element: A pure substance made of only one kind of atom. Examples: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N).

• Compound: A substance formed when two or more different elements combine chemically. Example: Water (H2O).

• Molecule: Two or more atoms bonded together. Example: O2 (oxygen gas).

• Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons. Example: Na+, Cl-.

• Isotope: Atoms of the same element with different numbers of neutrons. Example: Carbon-12 and Carbon-14.

• Valence Number: The number of electrons in the outermost shell, determining an atom's chemical reactivity.

• Electrolyte: A substance that dissociates into ions in solution and conducts electricity. Example: Sodium chloride (NaCl).

Medical Uses of Isotopes

• Radioisotopes are used in medical imaging (e.g., Technetium-99m in SPECT scans) and cancer treatment (e.g., Iodine-131 for thyroid therapy).

Major Elements of the Body

• Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N), Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg), Iron (Fe)

2.2 Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds. The type of bond affects the properties of substances in the body.

• Ionic Bond: Formed when electrons are transferred from one atom to another, creating oppositely charged ions that attract each other. Example: NaCl (sodium chloride)

• Polar Covalent Bond: Electrons are shared unequally between atoms, resulting in partial charges. Example: H2O (water)

• Nonpolar Covalent Bond: Electrons are shared equally between atoms. Example: O2 (oxygen gas)

• Hydrogen Bond: A weak attraction between a hydrogen atom (already covalently bonded to an electronegative atom) and another electronegative atom. Example: Between water molecules

• Strength of Bonds: Covalent bonds are the strongest, followed by ionic bonds, with hydrogen bonds being the weakest.

Summary Table: Types of Bonds

Bond Type	Strength	Example
Covalent (Nonpolar)	Strongest	O2
Covalent (Polar)	Strong	H2O
Ionic	Moderate	NaCl
Hydrogen	Weakest	Between H2O molecules

2.3 Chemical Reactions

Chemical reactions involve the making or breaking of bonds between atoms. They are essential for all physiological processes.

• Synthesis Reaction: Two or more substances combine to form a more complex substance. General Equation: $A + B \rightarrow AB$

• Decomposition Reaction: A complex substance breaks down into two or more simpler substances. General Equation: $AB \rightarrow A + B$

• Exchange Reaction: Parts of two molecules are exchanged to form two new compounds. General Equation: $AB + CD \rightarrow AD + CB$

• Reversible Reaction: The products can revert to the original reactants. General Equation: $A + B \rightleftharpoons AB$

2.4 Enzymes

Enzymes are biological catalysts that speed up chemical reactions in the body without being consumed.

• Enzyme: A protein that lowers the activation energy of a chemical reaction, increasing the reaction rate.

• Role in Chemical Reactions: Enzymes bind to substrates (reactants), convert them to products, and release them, ready to catalyze another reaction.

• Components of Enzymes:

  • Apoenzyme: The protein portion.

  • Cofactor: A non-protein component (may be a metal ion or coenzyme) required for enzyme activity.

2.5 Water and Its Functions

Water is the most abundant compound in the human body and is essential for life.

• Functions of Water:

  • Solvent for chemical reactions

  • Transport of substances

  • Temperature regulation

  • Lubrication and cushioning

2.6 The pH Scale and Body Fluids

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

• pH Scale: Ranges from 0 (most acidic) to 14 (most basic), with 7 being neutral.

• Acid: A substance that releases hydrogen ions (H+) in solution. Example: HCl

• Base: A substance that accepts hydrogen ions or releases hydroxide ions (OH-). Example: NaOH

• Normal pH of Body Fluids:

  • Blood: 7.35–7.45

  • Gastric juice: 1.5–3.5

  • Urine: 4.5–8.0

  • Saliva: 6.35–6.85

Summary Table: pH of Body Fluids

Fluid	Normal pH Range
Blood	7.35–7.45
Gastric Juice	1.5–3.5
Urine	4.5–8.0
Saliva	6.35–6.85

2.7 Buffer Systems and Blood pH

Buffer systems help maintain the pH of body fluids within a narrow range, which is critical for normal cellular function.

• Buffer: A substance that minimizes changes in pH by binding or releasing hydrogen ions.

• Example of Buffer System: The bicarbonate buffer system in blood:

$\mathrm{CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-}$

• Primary Buffer System in Blood: The bicarbonate (HCO3-) buffer system is the main mechanism for controlling blood pH.

• How Buffers Work: If blood becomes too acidic, bicarbonate ions bind excess H+ to form carbonic acid, which can be converted to CO2 and exhaled. If blood becomes too basic, carbonic acid dissociates to release H+.

Additional info: Other buffer systems include the phosphate buffer system and protein buffers (e.g., hemoglobin in red blood cells).