The human body is a precisely structured container of chemical reactions. Have you ever thought of yourself in this way? Probably not, and yet, in the strictly physical sense, that is what each of us is. The body consists of trillions of atoms in specific arrangements and thousands of chemical reactions proceeding in a very orderly manner.
That literally describes us, and yet it is clearly not the whole story. The keys to understanding human consciousness and self-awareness are still beyond our grasp. We do not yet know what enables us to study ourselves—no other animals do, as far as we know—but we have accumulated a great deal of knowledge about what we are made of and how it all works.
Some of this knowledge makes up the course you are about to take, a course in basic human anatomy and physiology. Anatomy is the study of body structure, which includes size, shape, composition, and perhaps even coloration. Physiology is the study of how the body functions.
The physiology of red blood cells, for example, includes what these cells do, how they do it, and how this is related to the functioning of the rest of the body. Physiology is directly related to anatomy. For example, red blood cells contain the mineral iron in molecules of the protein called hemoglobin; this is an aspect of their anatomy. The presence of iron enables red blood cells to carry oxygen, which is their function.
All cells in the body must receive oxygen in order to function properly, so the physiology of red blood cells is essential to the physiology of the body as a whole. Pathophysiology is the study of disorders of functioning, and a knowledge of normal physiology makes such disorders easier to understand. For example, you are probably familiar with anemia called iron deficiency anemia.
With insufficient iron in the diet, there will not be enough iron in the hemoglobin of red blood cells, and hence less oxygen will be transported throughout the body, resulting in the symptoms of the iron deficiency disorder. This example shows the relationship between anatomy, physiology, and pathophysiology. The purpose of this text is to enable you to gain an understanding of anatomy and physiology with an emphasis on normal structure and function.
Many examples of pathophysiology have been included, however, to illustrate the relationship of disease to normal physiology and to describe some of the procedures used in the diagnosis of disease. Many of the examples are clinical applications that will help you begin to apply what you have learned and demonstrate that your knowledge of anatomy and physiology will become the basis for your further study in the health professions.
LEVELS OF ORGANIZATION
The human body is organized into structural and functional levels of increasing complexity. Each higher-level incorporates the structures and functions of the previous level, as you will see. We will begin with the simplest level, which is the chemical level, and proceed to cells, tissues, organs, and organ systems. All of the levels of the organization are depicted in Fig
The chemicals that make up the body may be divided into two major categories: inorganic and organic. Inorganic chemicals are usually simple molecules made of one or two elements other than carbon (with a few exceptions). Examples of inorganic chemicals are water (H2O); oxygen (O2); one of the exceptions, carbon dioxide (CO2); and minerals such as iron (Fe), calcium (Ca), and sodium (Na). Organic chemicals are often very complex and always contain the elements carbon and hydrogen. In this category of organic chemicals are carbohydrates, fats, proteins, and nucleic acids. The chemical organization of the body is the subject of Chapter 2
The smallest living units of structure and function are cells. There are many different types of human cells, though they all have certain similarities. Each type of cell is made of chemicals and carries out specific chemical reactions. Cell structure and function are discussed in Chapter 3.
A tissue is a group of cells with similar structure and function. There are four groups of tissues: Epithelial tissues—cover or line body surfaces; some are capable of producing secretions with specific functions. The outer layer of the skin and sweat glands are examples of epithelial tissues. Internal epithelial tissues include the walls of capillaries (squamous epithelium) and the kidney tubules (cuboidal epithelium), as shown in Fig