Chemistry Comes Alive: Foundations for Anatomy & Physiology

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Chemistry Comes Alive: Foundations for Anatomy & Physiology

Introduction to Chemistry in Physiology

Chemistry is fundamental to understanding physiological processes in the human body. All body functions depend on chemical reactions, from movement and digestion to nerve impulses and cellular respiration.

Flowchart of chemical reactions in physiology

Matter and Energy

Definitions and Differences

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 effect of gravity on mass and can change with location.
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).

Mass vs Weight on Earth and Mars

Kinetic vs. Potential Energy

Kinetic Energy: Energy of motion; increases with mass or velocity.
Potential Energy: Stored energy due to position or structure; can be converted to kinetic energy when released.

Potential energy transforming into kinetic energy Potential and kinetic energy in a roller coaster

Forms of Energy

Chemical Energy: Stored in the bonds of chemical substances; released during chemical reactions (e.g., ATP hydrolysis in cells).
Electrical Energy: Results from the movement of charged particles (ions); essential for nerve impulses and muscle contraction.
Mechanical Energy: Directly involved in moving matter (e.g., muscle contraction, heart beating).
Radiant (Electromagnetic) Energy: Travels in waves; includes visible light, ultraviolet, X-rays, etc.

ATP and metabolism energy flow Muscle contraction as mechanical energy Electrical system of the heart Nerve impulse propagation Electromagnetic spectrum

Energy Conversion and Loss

Energy can be converted from one form to another, but some energy is always lost as heat during conversion (e.g., electrical energy to light and heat in a bulb).

Chemical Elements and Atoms

Elements and Their Importance

Element: A unique substance that cannot be broken down by ordinary chemical means. All matter is composed of elements.
The four major elements in the human body are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N), making up about 96% of body mass.

Carbon element symbol Oxygen element symbol Hydrogen element symbol Nitrogen element symbol

Element	Symbol	% Body Mass	Function
Oxygen	O	65.0	Component of organic/inorganic molecules; needed for ATP production
Carbon	C	18.5	Component of all organic molecules
Hydrogen	H	9.5	Component of organic molecules; influences pH
Nitrogen	N	3.3	Component of proteins and nucleic acids

Atoms and Subatomic Particles

Atom: The smallest unit of an element that retains its properties.
Subatomic particles: Protons (positive, in nucleus), Neutrons (neutral, in nucleus), Electrons (negative, in electron cloud).
Atoms are electrically neutral because the number of protons equals the number of electrons.

Models of the helium atom

Particle	Charge	Location	Mass (amu)
Proton	+1	Nucleus	1
Neutron	0	Nucleus	1
Electron	-1	Electron cloud	~0

Atomic Number, Mass, Isotopes, and Radioisotopes

Atomic Number: Number of protons in the nucleus.
Atomic Mass: Number of protons plus neutrons.
Isotopes: Atoms of the same element with different numbers of neutrons.
Radioisotopes: Unstable isotopes that decay, emitting radiation (radioactivity); used in medical diagnosis and research.
Half-life: Time required for half of a radioisotope to decay.

Atomic number and mass Isotopes of hydrogen Isotopes of carbon Decay of carbon-14

Molecules, Compounds, and Mixtures

Definitions

Molecule: Two or more atoms held together by chemical bonds.
Compound: Molecule composed of two or more different elements.
Mixture: Two or more substances physically intermixed, not chemically bonded.

Compound vs mixture

Types of Mixtures

Solutions: Homogeneous mixtures; solute particles are very small and do not settle out (e.g., salt water).
Colloids: Heterogeneous mixtures; solute particles are larger, do not settle out, and scatter light (e.g., cytosol).
Suspensions: Heterogeneous mixtures with large, visible solutes that settle out (e.g., blood).

Distinguishing Mixtures from Compounds

Mixtures involve no chemical bonding and can be separated by physical means; compounds involve chemical bonding and require chemical means to separate.

Concentration of Solutions

Expressed as percent, mg/dL, or molarity (M).
Mole: The molecular weight of a substance in grams; 1 mole contains particles (Avogadro's number).

Calculating molecular weight of glucose

Chemical Bonds and the Role of Electrons

Electron Shells and the Octet Rule

Electrons occupy energy levels (shells) around the nucleus; the outermost shell is the valence shell.
Octet Rule: Atoms tend to gain, lose, or share electrons to achieve 8 electrons in their valence shell (except H and He, which are stable with 2).

Types of Chemical Bonds

Ionic Bonds: Formed by the transfer of electrons from one atom to another, creating ions (cations and anions) that attract each other.
Covalent Bonds: Formed by the sharing of electrons between atoms; can be polar (unequal sharing) or nonpolar (equal sharing).
Hydrogen Bonds: Weak attractions between a hydrogen atom (covalently bonded to an electronegative atom) and another electronegative atom.

Ionic bond formation between Na and Cl Covalent bond formation in methane Polar and nonpolar molecules Summary table of chemical bond types

Chemical Reactions

Types of Chemical Reactions

Synthesis (Combination): Atoms or molecules combine to form a larger, more complex molecule. Example: Amino acids forming proteins.
Decomposition: A molecule is broken down into smaller molecules or atoms. Example: Glycogen breaking down to glucose.
Exchange (Displacement): Bonds are both made and broken; atoms are exchanged between molecules. Example: ATP transfers a phosphate to glucose.

Synthesis reaction example Decomposition reaction example Exchange reaction example

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).

OIL RIG mnemonic for redox Redox reaction in 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 (e.g., 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.

References

Marieb, Elaine N., and Katja Hoehn. Human Anatomy & Physiology. 11th ed., Pearson, 2018.