Chemistry and Physiological Reactions: Foundations for Anatomy & Physiology

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Chapter 2: Chemistry Comes Alive

Introduction to Chemistry in Physiology

Chemistry forms the basis of all physiological reactions in the human body, including movement, digestion, heart function, and nervous system activity. Understanding basic chemistry and biochemistry is essential for comprehending how the body operates at the molecular level.

Basic Chemistry: Covers atomic structure, elements, and chemical bonds.
Biochemistry: Focuses on the chemical composition and reactions of living matter.

Basic Chemistry Review

Elements and Atomic Structure

Elements are fundamental substances listed in the periodic table. Atoms, the smallest units of elements, consist of subatomic particles: protons (positive charge), neutrons (no charge), and electrons (negative charge).

Atomic Number: Number of protons in an atom, unique to each element.
Atomic Weight: Sum of protons and neutrons in the nucleus.

Atomic structure of hydrogen, helium, and lithium

Example: Hydrogen (1 proton, 0 neutrons, 1 electron), Helium (2 protons, 2 neutrons, 2 electrons), Lithium (3 protons, 4 neutrons, 3 electrons).

The Periodic Table of Elements

The periodic table organizes all known elements by their atomic number and properties. It is a fundamental reference for understanding chemical behavior.

Periodic Table of Elements

Elements in the Human Body

The human body is composed primarily of oxygen, carbon, hydrogen, and nitrogen, with lesser and trace elements playing vital roles in physiological functions.

Major Elements: Oxygen, Carbon, Hydrogen, Nitrogen
Lesser Elements: Calcium, Phosphorus, Potassium, Sulfur, Sodium, Chlorine, Magnesium
Trace Elements: Iodine, Iron, and others required in minute amounts

Example: Iron is essential for hemoglobin function; iodine is necessary for thyroid hormones.

Combining Matter: Molecules, Compounds, and Mixtures

Molecules vs. Compounds

Atoms combine to form molecules and compounds. A molecule consists of two or more atoms of the same element, while a compound contains atoms of different elements.

Molecule Example: O2 (oxygen gas)
Compound Example: C6H12O6 (glucose)

Mixtures: Solutions, Colloids, and Suspensions

Most matter exists as mixtures, which are physical combinations of two or more components. The three main types are solutions, colloids, and suspensions.

Solutions: Homogeneous mixtures with evenly distributed particles. Solute is dissolved in a solvent (usually water).

Solution: mineral water example

Colloids: Heterogeneous mixtures with larger particles that scatter light but do not settle out.

Colloid: Jell-O example

Suspensions: Heterogeneous mixtures with large particles that settle out over time.

Suspension: blood example

Key Differences: Mixtures can be separated by physical means and may be homogeneous or heterogeneous, while compounds require chemical bonds and are always homogeneous.

Measurement of Solution Concentration

Concentration can be expressed as percent, milligrams per deciliter (mg/dL), or molarity (M). Molarity is based on the number of moles of solute per liter of solvent, using Avogadro’s number ( molecules per mole).

Example: 1 M solution of glucose contains 180.12 grams of glucose per liter.

Types of Chemical Bonds

Ionic Bonds

Ionic bonds involve the transfer of electrons from one atom to another, resulting in charged ions. The attraction between oppositely charged ions forms the bond.

Anion: Atom that gains electrons (negative charge)
Cation: Atom that loses electrons (positive charge)

Covalent Bonds

Covalent bonds are formed by the sharing of electrons between atoms. They can be single, double, or triple bonds depending on the number of shared electron pairs.

Formation of methane by covalent bonding

Nonpolar Covalent Bonds: Equal sharing of electrons (e.g., CO2)
Polar Covalent Bonds: Unequal sharing, resulting in partial charges (e.g., H2O)

Comparison of ionic, polar covalent, and nonpolar covalent bonds

Hydrogen Bonds

Hydrogen bonds are weak attractions between the electropositive hydrogen of one molecule and the electronegative atom of another. They are crucial for the properties of water and the three-dimensional structure of large molecules.

Hydrogen bonding between water molecules

Example: Hydrogen bonds give water its liquid state and surface tension.

Water strider on pond due to surface tension from hydrogen bonds

Summary Table: Major Chemical Bond Types

Type	Description	Strength
Covalent bonds	Sharing of pairs of electrons; may be polar or nonpolar	Strongest
Ionic bonds	Attraction between oppositely charged ions	Intermediate
Hydrogen bonds	Attraction between hydrogen and electronegative atom	Weakest

Chemical Reactions

Chemical Equations

Chemical reactions involve the formation, rearrangement, or breaking of chemical bonds. They are represented by chemical equations showing reactants and products.

Example:

Types of Chemical Reactions

Synthesis (Combination) Reactions: Atoms or molecules combine to form larger, more complex molecules. Used in anabolic processes.

Synthesis reaction: formation of protein from amino acids

Decomposition Reactions: Breakdown of a molecule into smaller molecules or atoms. Involve catabolic reactions.

Decomposition reaction: breakdown of glycogen to glucose

Exchange (Displacement) Reactions: Bonds are both made and broken; involve both synthesis and decomposition.

Exchange reaction: ATP transfers phosphate to glucose

Redox Reactions: In living systems, exchange reactions often involve reduction (gain of electrons) and oxidation (loss of electrons).

Factors Affecting Rate of Chemical Reactions

Temperature: Higher temperatures increase reaction rate.
Concentration: Higher concentration increases rate.
Particle Size: Smaller particles increase rate.
pH: Can affect reaction rate.
Catalysts: Increase reaction rate without being consumed; enzymes are biological catalysts.

Biochemistry: Organic and Inorganic Compounds

Inorganic Compounds

Inorganic compounds include water, salts, acids, and bases. They do not contain carbon and are essential for physiological processes.

Water: Most abundant inorganic compound; properties include high heat capacity, high heat of vaporization, polar solvent properties, reactivity, and cushioning.

Example: Cerebrospinal fluid cushions nervous system organs.

Salts: Ionic compounds that dissociate into ions in water; important for electrical conductivity and homeostasis.
Acids and Bases: Acids are proton donors; bases are proton acceptors. Both are electrolytes and affect pH.

pH: Acid-Base Concentration

pH measures the concentration of hydrogen ions in solution. Acidic solutions have high [H+] and low pH; alkaline solutions have low [H+] and high pH. Neutral solutions have equal H+ and OH– ions.

pH scale with examples

Neutralization: Mixing acids and bases forms water and a salt.
Buffers: Resist changes in pH by releasing or binding H+ ions; important for maintaining homeostasis.

Example: Carbonic acid–bicarbonate system is a key buffer in blood.

Summary

Understanding basic chemistry, including atomic structure, elements, chemical bonds, and reactions, is fundamental for studying anatomy and physiology. These principles explain how the body’s molecules interact, how energy is transferred, and how homeostasis is maintained.