Chemistry Comes Alive

Introduction to Chemistry in Anatomy & Physiology

Chemistry is fundamental to understanding physiology because all biological processes are driven by chemical reactions. Human biochemistry involves a series of required chemical (metabolic) reactions occurring in cells, making chemical principles essential for comprehending how the body functions.

Matter, Space, & Mass

Definitions and Properties

• Matter: A physical substance that occupies space and has mass. It exists in three states: solid, liquid, and gas, each differing in shape and volume.

• Space: The measurable three-dimensional area occupied by an object.

• Mass: The amount of matter in an object, which remains constant regardless of gravity or shape.

• Weight is the force exerted by gravity on mass.

States of Matter: Solids have definite shape and volume, liquids have definite volume but take the shape of their container, and gases have neither definite shape nor volume.

Energy & Energy Conversion

Types and Forms of Energy

• Energy: The capacity to do work or put matter into motion.

• Potential Energy: Stored energy due to position or structure.

• Kinetic Energy: Energy in action, causing movement of objects.

• Forms of Energy:

  • Chemical: Stored in chemical bonds (e.g., ATP in cells).

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

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

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

Energy Conversion: Energy can be transformed from one form to another (e.g., chemical to mechanical in muscle contraction). These conversions are often inefficient, with some energy lost as heat, which is not available to do work.

Elements and Atoms

Basic Building Blocks of Matter

• Element: A unique substance that cannot be broken down by ordinary chemical means. Each element is represented by a chemical symbol (e.g., Na for sodium).

• Atom: The smallest unit of an element that retains its properties. Atoms consist of a nucleus (protons and neutrons) and electrons orbiting the nucleus.

Major Elements in the Human Body: Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N) make up 96% of body weight. Minor elements (minerals and trace elements) are required in smaller amounts, such as calcium (Ca), phosphorus (P), potassium (K), and iron (Fe).

Atomic Structure

Subatomic Particles and Models

• Protons (p+): Positively charged, 1 atomic mass unit (amu).

• Neutrons (n0): No charge, 1 amu.

• Electrons (e-): Negatively charged, negligible mass (1/2000 of a proton).

• Electrons are attracted to the nucleus by the positive charge of protons.

There are two main models for atomic structure:

• Planetary Model: Electrons move in fixed, circular orbits around the nucleus (2D).

• Orbital Model: Electrons are found in regions (clouds) around the nucleus (3D).

Element Identification

Atomic Number, Mass Number, and Isotopes

• Atomic Number: Number of protons in the nucleus (defines the element).

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

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

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

• Radioisotopes: Unstable isotopes that decay over time, emitting radiation (e.g., 14C used in carbon dating).

Example Calculation: For lithium (Li):

Molecules & Compounds

Formation and Types

• Molecule: A combination of two or more atoms held together by chemical bonds.

• Elemental Molecule: Consists of two or more atoms of the same element (e.g., O2).

• Compound Molecule: Consists of atoms of different elements (e.g., H2O, NaCl).

Example: The reaction between sodium metal and chlorine gas produces sodium chloride (table salt):

Chemical Reactions & Metabolism

Basic Principles

• Chemical Reaction: A process in which the identity of at least one substance changes, forming new products.

• Requirements for a Reaction:

  • Reactants: Substances that react together.

  • Permissible Environment: Suitable conditions for the reaction.

  • Time: Rate at which the reaction occurs.

• Metabolism: The sum of all chemical reactions in the body, including those that build up (anabolism) and break down (catabolism) molecules.

Example: The formation of sodium chloride from sodium and chlorine is a classic example of a chemical reaction essential for physiology.

Summary Table: Key Concepts in Chemistry for Anatomy & Physiology