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Organization and General Plan of the Body

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  Organization and General Plan of the Body T he human body is a precisely structured container   of chemical reactions. Have you ever thought of your-self 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 accumu-lated 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
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Levels of Organization

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  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 pro-ceed to cells, tissues, organs, and organ systems. All of the levels of organization are depicted in Fig. 1–1. CHEMICALS 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 (H 2 O); oxygen (O 2 ); one of the exceptions, car-bon dioxide (CO 2 ); and minerals such as iron (Fe), cal-cium (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 ac
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Metabolism and Homeostasis

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  METABOLISM AND HOMEOSTASIS Metabolism  is a collective noun; it is all of the chem-ical reactions and physical processes that take place within the body. Metabolism includes growing, repair-ing, reacting, and reproducing—all the characteristics of life. The pumping of the heart, the digestion of food in the stomach, the diffusion of gases in the lungs and tissues, and the production of energy in each cell of the body are just a few of the thousands of aspects of metabolism.  Metabolism  comes from a Greek word meaning “change,” and the body is always changing in visible ways (walking down the street), microscopic ways (cells dividing in the skin to produce new epider-mis), and submicroscopic or molecular ways (RNA and enzymes constructing new proteins). A related concept,  metabolic rate , is most often used to mean the speed at which the body produces energy and heat, or, put another way, energy production per unit of time, such as 24 hours. Metabolic rate, therefore, is one aspect
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Terminology and General Plan of the Body

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  TERMINOLOGY AND GENERAL PLAN OF THE BODY As part of your course in anatomy and physiology, you will learn many new words or terms. At times you may feel that you are learning a second language, and indeed you are. Each term has a precise meaning, which is understood by everyone else who has learned the language. Mastering the terminology of your pro-fession is essential to enable you to communicate effec-tively with your coworkers and your future patients. Although the number of new terms may seem a bit overwhelming at first, you will find that their use soon becomes second nature to you.   BODY PARTS AND AREAS Each of the terms listed in Table 1–2 and shown in Fig. 1–4 refers to a specific part or area of the body. For example, the term  femoral always refers to the thigh. The femoral artery is a blood vessel that passes through the thigh, and the quadriceps femoris is a large muscle group of the thigh. Another example is  pulmonary , which always refers to the lungs, as in pulmonar
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Elements

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  ELEMENTS All matter, both living and not living, is made of ele-ments, the simplest chemicals. An  element  is a sub-stance made of only one type of atom (therefore, an atom is the smallest part of an element). There are 92 naturally occurring elements in the world around us. Examples are hydrogen (H), iron (Fe), oxygen (O), calcium (Ca), nitrogen (N), and carbon (C). In nature, an element does not usually exist by itself but rather combines with the atoms of other elements to form compounds. Examples of some compounds important to our study of the human body are water (H 2 O), in which two atoms of hydrogen combine with one atom of oxygen; carbon dioxide (CO 2 ), in which an atom of carbon combines with two atoms of oxygen; and glu-cose (C 6 H 12 O 6 ), in which six carbon atoms and six oxygen atoms combine with 12 hydrogen atoms. The elements carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur are found in all living things. If calcium is included, these seven elements make
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Atoms

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  ATOMS Atoms  are the smallest parts of an element that have   the characteristics of that element. An atom consists of three major subunits or particles: protons, neutrons, and electrons (Fig. 2–1). A  proton  has a positive elec-trical charge and is found in the nucleus (or center) of the atom. A  neutron  is electrically neutral (has no charge) and is also found in the nucleus. An  electron  has a negative electrical charge and is found outside the nucleus orbiting in what may be called an electron cloud or shell around the nucleus. Figure 2–1.  An atom of carbon. The nucleus contains   six protons and six neutrons (not all are visible here). Six electrons orbit the nucleus, two in the first energy level and four in the second energy level. QUESTION:  What is the electrical charge of this atom as   a whole?   The number of protons in an atom gives it its  atomic number . Protons and neutrons have mass and   weight; they give an atom its atomic weight . In an atom, the number of pro
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Chemical Bonds

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  CHEMICAL BONDS A chemical bond is not a structure, but rather a force or attraction between positive and negative electrical charges that keeps two or more atoms closely associ-ated with each other to form a molecule. By way of comparison, think of gravity. We know that gravity is not a “thing,” but rather the force that keeps our feet on the floor and allows us to pour coffee with consis- often have physical characteristics different from those of the atoms of the original elements. For example, the elements hydrogen and oxygen are gases, but atoms of each may chemically bond to form molecules of water, which is a liquid. The type of chemical bonding depends upon the tendencies of the electrons of atoms involved, as you will see. Four kinds of bonds are very important to the chemistry of the body: ionic bonds, covalent bonds, disulfide bonds, and hydrogen bonds. IONIC BONDS An  ionic bond  involves  the loss of one or more elec-trons by one atom and the gain of the electron(s) by an
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