Chemistry Comes Alive: Foundations for Anatomy & Physiology

Chemistry Comes Alive

Introduction to Chemistry in Physiology

Chemical reactions are fundamental to all physiological processes in the human body. Understanding basic chemistry is essential for comprehending how the body functions at the molecular and cellular levels.

Matter and Energy

Definitions and Properties

• Matter: Anything that occupies space and has mass. Mass is the amount of matter in an object and remains constant regardless of location, while weight is the force exerted by gravity on that mass.

• Energy: The capacity to do work or put matter into motion. Energy exists in two main forms: kinetic energy (energy in action) and potential energy (stored energy).

States of Matter

• Solids: Definite shape and volume (e.g., bones).

• Liquids: Definite volume, conform to container shape (e.g., blood).

• Gases: No definite shape or volume (e.g., air in lungs).

Forms of Energy

• Chemical Energy: Stored in bonds of chemical substances; released during chemical reactions (e.g., ATP hydrolysis).

• Electrical Energy: Results from movement of charged particles (e.g., nerve impulses, heart contractions).

• Mechanical Energy: Directly involved in moving matter (e.g., muscle contraction).

• Radiant (Electromagnetic) Energy: Travels in waves (e.g., visible light, X-rays, UV rays).

Elements and Atoms

Chemical Elements

Elements are unique substances that cannot be broken down into simpler substances by ordinary chemical methods. The four major elements that make up about 96% of body mass are:

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

Structure of Atoms

• Protons: Positive charge, located in the nucleus, mass = 1 amu.

• Neutrons: No charge, located in the nucleus, mass = 1 amu.

• Electrons: Negative charge, orbit the nucleus in electron clouds, mass ≈ 0 amu.

Atomic Number, Mass, and Isotopes

• Atomic Number: Number of protons in the nucleus.

• Atomic Mass: Sum of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Radioisotopes: Unstable isotopes that decay, emitting radiation (radioactivity).

• Atomic Weight: Average of the mass numbers of all isotopes of an element.

Molecules, Compounds, and Mixtures

Definitions

• Molecule: Two or more atoms held together by chemical bonds.

• Compound: Molecule containing two or more different elements.

• Mixture: Substances composed of two or more components physically intermixed (not chemically bonded).

Types of Mixtures

• Solutions: Homogeneous mixtures; solute particles are very tiny and do not settle out or scatter light (e.g., saline solution).

• Colloids: Heterogeneous mixtures; solute particles are larger than in solutions and scatter light but do not settle out (e.g., cytosol).

• Suspensions: Heterogeneous mixtures with large, visible solutes that tend to settle out (e.g., blood).

Concentration of Solutions

• Percent (%): Parts per 100 parts of solution.

• Milligrams per deciliter (mg/dL): Mass of solute per 100 mL of solution.

• Molarity (M): Moles of solute per liter of solution. 1 mole = molecular weight in grams.

Chemical Bonds

Role of Electrons and the Octet Rule

Electrons occupy energy levels (shells) around the nucleus. The octet rule states that atoms tend to gain, lose, or share electrons to achieve eight electrons in their valence shell, driving chemical bonding.

Types of Chemical Bonds

• Ionic Bonds: Formed by the transfer of electrons from one atom to another, resulting in charged ions (cations and anions) that attract each other (e.g., NaCl).

• Covalent Bonds: Formed by the sharing of electrons between atoms. Can be nonpolar (equal sharing) or polar (unequal sharing).

• Hydrogen Bonds: Weak attractions between a hydrogen atom (covalently bonded to an electronegative atom) and another electronegative atom.

Chemical Reactions

Types of Chemical Reactions

• Synthesis (Combination): Atoms or molecules combine to form a larger, more complex molecule. $A + B \rightarrow AB$

• Decomposition: A molecule is broken down into smaller molecules or atoms. $AB \rightarrow A + B$

• Exchange (Displacement): Bonds are both made and broken; atoms are rearranged. $AB + C \rightarrow AC + B$

Oxidation-Reduction (Redox) Reactions

• Oxidation: Loss of electrons (electron donor is oxidized).

• Reduction: Gain of electrons (electron acceptor is reduced).

• Redox reactions are essential for energy transfer in metabolism (e.g., cellular respiration).

Energy Flow in Chemical Reactions

• Exergonic Reactions: Release energy; products have less potential energy than reactants (e.g., catabolic and oxidative reactions).

• Endergonic Reactions: Absorb energy; products have more potential energy than reactants (e.g., anabolic reactions).

Irreversibility of Reactions in the Body

• Many biological reactions are irreversible due to large energy release or removal of products.

• Example: Glucose oxidation to CO2 and H2O.

Factors Affecting Reaction Rates

• Temperature: Higher temperature increases reaction rate (up to a point).

• Concentration: Higher concentration of reactants increases rate.

• Particle Size: Smaller particles react faster.

• Catalysts/Enzymes: Speed up reactions without being consumed.

Summary Table: Major Chemical Bond Types

Type	Description	Strength
Covalent bonds	Sharing of pairs of electrons. May be polar (not equally shared) or nonpolar (equally shared).	Strongest
Ionic bonds	Attraction between two oppositely charged ions.	Intermediate
Hydrogen bonds	Attraction between a hydrogen atom carrying a partial positive charge (δ+) and an electronegative atom with a slightly negative charge (δ-).	Weakest

Additional info: This guide covers the foundational chemistry concepts necessary for understanding physiological processes, as outlined in Chapter 2: Chemistry Comes Alive, of a typical Anatomy & Physiology course.