Chemistry in Anatomy & Physiology

All physiological processes in the human body, such as movement, digestion, and heart pumping, rely on chemical reactions. Understanding basic chemistry is essential for studying anatomy and physiology.

• The four main elements in the human body are carbon, hydrogen, oxygen, and nitrogen (C, H, O, N).

Atoms

Structure of Atoms

Atoms are the fundamental units of matter, composed of three types of subatomic particles.

• Protons: Positively charged particles found in the nucleus.

• Neutrons: Neutral particles (no charge) also found in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus.

• A neutral atom has an equal number of protons and electrons, resulting in a net charge of zero.

Nucleus

• Contains protons and neutrons.

• Protons have a positive charge; neutrons are neutral.

• The nucleus is orbited by electrons (negative charge).

Orbitals

• Electrons move in regions called orbitals around the nucleus.

Identifying Elements

• Atomic number: Number of protons in the nucleus (also equals the number of electrons in a neutral atom).

• Mass number: Sum of protons and neutrons in the nucleus.

Example: Carbon has an atomic number of 6 (6 protons, 6 electrons) and a mass number of 12 (6 protons + 6 neutrons).

Electrons and Chemical Bonding

Electrons determine how atoms react chemically. Chemical reactions involve the sharing, loss, or gain of electrons.

• The number of electron shells/levels depends on the number of electrons.

• Octet rule: Atoms are stable when they have 8 electrons in their outer shell (except for the first shell, which holds 2).

Types of Chemical Bonds

• Ionic bond

• Covalent bond

• Hydrogen bond (weak chemical bond)

Ionic Bonds

Formed by the transfer of one or more electrons from one atom to another, resulting in charged ions.

• Anion: Atom that gains an electron (net negative charge).

• Cation: Atom that loses an electron (net positive charge).

• Ionic bonds result in attraction between oppositely charged ions (e.g., NaCl).

• Salt: General term for ionic compounds.

Covalent Bonds

Formed when atoms share electrons rather than transfer them.

• Electrons are shared between atoms.

• Single, double, or triple bonds can form depending on the number of shared electron pairs.

• Example: H2 (single bond), O2 (double bond), N2 (triple bond).

• Carbon can form up to 4 covalent bonds (e.g., CH4).

Polar vs. Non-polar Covalent Molecules

• Non-polar: Even sharing of electrons; no partial charges (e.g., fats, oils).

• Polar: Uneven sharing of electrons; partial positive and negative charges (e.g., water).

• Electronegativity: The ability of an atom to attract electrons. Higher electronegativity means stronger pull on electrons.

• The shape and orientation of atoms affect polarity.

Examples: Carbon dioxide (CO2) is non-polar; water (H2O) is polar.

Hydrogen Bonds

Weak attractions (not true bonds) between a hydrogen atom covalently bonded to one electronegative atom and another electronegative atom (e.g., O, N, F).

• Responsible for water's surface tension and high boiling point.

• Allow water molecules to stick together (cohesion).

• Important in the structure of proteins and DNA.

Chemical Equations

Chemical equations represent chemical reactions. The arrow (→) means "yields" or "produces".

• Reactants: Substances that start the reaction (left side).

• Products: Substances formed by the reaction (right side).

Example: A + B → AB

Types of Chemical Reactions

• Synthesis (Anabolic) Reaction: Atoms or molecules combine to form larger molecules.

• Decomposition (Catabolic) Reaction: Molecules are broken down into smaller molecules or atoms.

• Exchange (Displacement) Reaction: Involves both synthesis and decomposition; parts are exchanged.

• Redox (Oxidation-Reduction) Reaction: Electrons are transferred between reactants. Oxidized: Loses electrons; Reduced: Gains electrons.

Mnemonic: OIL RIG (Oxidation Is Loss, Reduction Is Gain of electrons).

Biochemistry: Organic and Inorganic Compounds

Biochemistry studies the chemical composition and reactions of living matter.

• Organic compounds: Contain carbon (exceptions: CO2 and CO are inorganic).

• Inorganic compounds: All other compounds, most lack carbon.

Essential Inorganic Compounds

• Water (H2O): Universal solvent, reactant, and cushion (e.g., cerebrospinal fluid).

• Salts: Ionic compounds that dissociate in water to form ions (e.g., Na+, Cl-).

• Acids: Release H+ ions (protons) in solution; have low pH (0-6.9).

• Bases: Accept H+ ions or release OH-; have high pH (7.1-14).

Functions of Inorganic Ions

• Conduct electricity in solution.

• Involved in nerve impulse conduction, muscle contraction, and oxygen transport in blood.

Essential Organic Compounds

Carbon-Based Molecules

• Carbon is electroneutral (always shares electrons, never gains or loses).

• Can form up to 4 covalent bonds, allowing for complex structures (chains, rings).

Monomers and Polymers

• Monomer: The repeating unit in a polymer (e.g., glucose in starch).

• Polymer: Long chain of monomers.

• Hydrolysis: Breaking polymers into monomers by adding water.

Major Classes of Organic Compounds

• Carbohydrates: Sugars and starches; provide energy.

• Lipids: Fats, oils, steroids; energy storage and cell membranes.

• Proteins: Structural and functional molecules (enzymes, hormones).

• Nucleic acids: DNA and RNA; store and transmit genetic information.

Carbohydrates

Carbohydrates are classified by size and solubility.

• Monosaccharides: Simple sugars (e.g., glucose).

• Disaccharides: Two monosaccharides joined together (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen).

• Solubility: Larger carbohydrates are less soluble in water.

Example: Soluble and insoluble fiber are classified by their solubility.