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## Essentials of Human Anatomy and Physiology ### **28** That is, we are studying large, easily observable structures. Indeed, the term anatomy, derived from the Greek words meaning to cut (tomy) apart (ana), is related most closely to gross anatomical studies because in such studies, preserved an...

## Essentials of Human Anatomy and Physiology ### **28** That is, we are studying large, easily observable structures. Indeed, the term anatomy, derived from the Greek words meaning to cut (tomy) apart (ana), is related most closely to gross anatomical studies because in such studies, preserved animals or their organs are dissected (cut up) to be examined. Microscopic anatomy, in contrast, is the study of body structures that are too small to be seen with the naked eye. The cells and tissues of the body can only be seen through a microscope. ### **Physiology** Physiology (fiz"e-ol'o-je) is the study of how the body and its parts work or function (physio = nature; ology = the study of). Like anatomy, physiology has many subdivisions. For example, neurophysiology explains the workings of the nervous system, and cardiac physiology studies the function of the heart. ### **Relationship between Anatomy and Physiology** Anatomy and physiology are always inseparable. The parts of your body form a well-organized unit, and each of those parts has a job to do to make the body operate as a whole. Structure determines what functions can take place. For example, the lungs are not muscular chambers like the heart and so cannot pump blood through the body, but because the walls of their air sacs are very thin, they can exchange gases and provide oxygen to the body. We stress the intimate relationship between anatomy and physiology throughout this text to make your learning meaningful. ### **Did You Get It?** 1. Why would you have a hard time learning and understanding physiology if you did not also understand anatomy? 2. Kidney function, bone growth, and beating of the heart are all topics of anatomy. True or false? For answers; see Appendix A. **CONCEPTLINK** Throughout this text, Concept Links will highlight links between concepts and/or organ systems. Keep in mind that although discussions of the systems are separated into chapters for detailed study, the overall goal of this text is for you not only to gain an understanding of each individual system, but also to learn how the body systems interact to sustain life. ### **Levels of Structural Organization** **Learning Objectives** * Name the six levels of structural organization that make up the human body, and explain how they are related. * Name the organ systems of the body, and briefly state the major functions of each system. * Identify and classify by organ system all organs discussed. ### **From Atoms to Organisms** The human body exhibits many levels of structural complexity. The simplest level of the structural ladder is the chemical level (covered in Chapter 2). At this level, $atoms$, tiny building blocks of matter, combine to form $molecules$ such as water, sugar, and proteins, like those that make up our muscles. Molecules, in turn, associate in specific ways to form microscopic $cells$, the smallest units of all living things. (We will examine the cellular level in Chapter 3.) All cells have some common structures and functions, but individual cells vary widely in size, shape, and their particular roles in the body. The simplest living creatures are composed of single cells, but in complex organisms such as trees or human beings, the structural ladder continues on to the $tissue$ level. $Tissues$ consist of groups of similar cells that have a common function. There are four basic tissue types, and each plays a definite but different role in the body. (We discuss tissues in Chapter 3.) An $organ$ is a structure composed of two or more tissue types that performs a specific function for the body. At the $organ$ level of organization, extremely complex functions become possible. For example, the small intestine, which digests and absorbs food, is composed of all four