Chemistry Comes Alive: Foundations for Anatomy & Physiology

Chemistry in Anatomy & Physiology

Introduction to Chemistry in the Human Body

Chemistry is fundamental to understanding the structure and function of the human body. All physiological processes depend on chemical interactions at the molecular and atomic levels. This section introduces the essential chemical principles relevant to anatomy and physiology.

Basic Terminology and Concepts

Matter

• Matter is anything that has mass and occupies space.

• Matter can be seen, smelled, and/or felt.

• Weight is mass plus the effects of gravity.

States of Matter

• Solid: Definite shape and volume.

• Liquid: Changeable shape; definite volume.

• Gas: Changeable shape and volume.

Energy

• Energy is the capacity to do work or put matter into motion.

• The greater the work done, the more energy is used up.

• Energy can be converted from one form to another, but conversions are often inefficient (some energy is lost as heat).

Atoms and Elements

Atoms

• Atoms are the unique building blocks for each element.

• They are the smallest particles of an element that retain the properties of that element.

• Atoms give each element its particular physical and chemical properties.

• Composed of three subatomic particles:

  • Protons (positively charged)

  • Neutrons (neutral)

  • Electrons (negatively charged)

Elements

• An element is a substance that cannot be broken down into simpler substances by ordinary chemical means.

• Each element is defined by its number of protons (atomic number).

• The Periodic Table organizes elements by increasing atomic number and similar properties.

Isotopes and Atomic Structure

• Isotopes are structural variations of the same element; they have the same number of protons but different numbers of neutrons.

• Atomic number: Number of protons in the nucleus.

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

• Radioisotopes are unstable isotopes that emit radiation; useful in medical imaging and research, but can be harmful to living tissue.

Elements Composing the Human Body

Major Elements

About 96% of the human body is composed of four major elements: oxygen, carbon, hydrogen, and nitrogen. These elements are essential for life and are involved in the structure and function of biomolecules.

Element	Atomic Symbol	Approx. % Body Mass	Functions
Oxygen	O	65.0	Component of both organic (carbon-containing) and inorganic molecules; as a gas, essential for cellular energy (ATP) production.
Carbon	C	18.5	Component of all organic molecules, including carbohydrates, lipids, proteins, and nucleic acids.
Hydrogen	H	9.5	Component of all organic molecules; as an ion (proton), influences pH of body fluids.
Nitrogen	N	3.3	Component of proteins and nucleic acids (genetic material).

Other Essential Elements

Element	Atomic Symbol	Approx. % Body Mass	Functions
Calcium	Ca	1.5	Found in bones and teeth; required for muscle contraction, nerve conduction, and blood clotting.
Phosphorus	P	1.0	Part of bones and teeth; present in nucleic acids and ATP.
Potassium	K	0.4	Major positive ion (cation) in cells; necessary for nerve impulse conduction and muscle contraction.
Sulfur	S	0.3	Component of proteins, especially muscle proteins.
Sodium	Na	0.2	Major positive ion in extracellular fluids; important for water balance, nerve impulses, and muscle contraction.
Chlorine	Cl	0.2	Major negative ion (anion) in extracellular fluids.
Magnesium	Mg	0.1	Present in bone; important cofactor in metabolic reactions.

Trace elements (e.g., chromium, cobalt, copper, fluorine, manganese, molybdenum, selenium, silicon, tin, vanadium, zinc) are required in very small amounts, often as enzyme cofactors.

Compounds and Mixtures

Molecules and Compounds

• Molecule: Two or more atoms bonded together (e.g., O2).

• Compound: A molecule containing two or more different kinds of atoms (e.g., H2O).

Mixtures

• Most matter exists as mixtures: two or more components physically intermixed.

• Types of mixtures:

  • Solutions: Homogeneous mixtures (e.g., saline solution).

  • Colloids: Heterogeneous mixtures with larger particles (e.g., cytosol).

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

• Differences between mixtures and compounds:

  • Mixtures do not involve chemical bonding; compounds do.

  • Mixtures can be separated by physical means; compounds require chemical reactions to separate.

  • Mixtures can be homogeneous or heterogeneous; compounds are always homogeneous.

Chemical Bonds

Types of Chemical Bonds

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

• Covalent Bonds: Involve the sharing of two or more valence electrons between atoms. Can be single, double, or triple bonds depending on the number of shared electron pairs.

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

Polar vs. Nonpolar Covalent Bonds

• Nonpolar: Electrons are shared equally (e.g., O2, CO2).

• Polar: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

Summary Table: Major Chemical Bond Types

Bond Type	Description	Relative Strength
Covalent	Sharing of electron pairs; may be polar or nonpolar	Strongest
Ionic	Attraction between oppositely charged ions	Intermediate
Hydrogen	Attraction between a hydrogen atom and an electronegative atom	Weakest

Chemical Reactions

Chemical Equations

• Chemical reactions occur when chemical bonds are formed, rearranged, or broken.

• Represented by chemical equations showing reactants and products.

• Balanced equations indicate the relative amounts of each substance.

Types of Chemical Reactions

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

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

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

• Redox (Oxidation-Reduction): Involves the transfer of electrons between atoms. Example: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP$

Energy Flow in Chemical Reactions

• Exergonic reactions: Release energy (e.g., catabolic and oxidative reactions).

• Endergonic reactions: Absorb energy (e.g., anabolic reactions).

Reversibility of Chemical Reactions

• Many chemical reactions are theoretically reversible: $A + B \rightleftharpoons AB$

• In biological systems, many reactions are effectively irreversible due to high energy requirements or removal of products.

Factors Affecting Reaction Rates

• Temperature, concentration of reactants, particle size, and the presence of catalysts (such as enzymes) can all affect the rate of chemical reactions.

Example: Enzymes in the body act as catalysts to speed up biochemical reactions necessary for life.