The Human Body: An Orientation – PHSchool.com

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1
An Overview of Anatomy
and Physiology (pp. 23)



                                                   The Human
  Topics of Anatomy (p. 2)

  Topics of Physiology (pp. 23)

  Complementarity of Structure
  and Function (p. 3)

Levels of Structural
Organization (pp. 34)

Maintaining Life (pp. 48)
                                                     Body: An
  Necessary Life Functions (pp. 48)

  Survival Needs (p. 8)

Homeostasis (pp. 811)
                                                   Orientation
  Homeostatic Control (pp. 911)



                                            W
                                                      elcome to the study of one of the most fascinating subjects
  Homeostatic Imbalance (p. 11)
                                                      possible--your own body. Such a study is not only highly
The Language of Anatomy (pp. 1120)                   personal, but timely as well. We get news of some medical
                                            advance almost daily. To appreciate emerging discoveries in genetic
  Anatomical Position and Directional
  Terms (p. 13)
                                            engineering, to understand new techniques for detecting and treating
                                            disease, and to make use of published facts on how to stay healthy, you'll
  Regional Terms (p. 14)                    find it helpful to learn about the workings of your body. If you are
  Anatomical Variability (p. 14)            preparing for a career in the health sciences, the study of anatomy and
  Body Planes and Sections (p. 14)
                                            physiology has added rewards because it provides the foundation
                                            needed to support your clinical experiences.
  Body Cavities and Membranes (pp. 1420)




                                                                                                                    1
    2           U NI T 1 Organization of the Body

       In this chapter we define and contrast anatomy and physiol-            Another subdivision of gross anatomy is surface anatomy,
    ogy and discuss how the human body is organized. Then we re-          the study of internal structures as they relate to the overlying
    view needs and functional processes common to all living              skin surface. You use surface anatomy when you identify the
    organisms. Three essential concepts--the complementarity of           bulging muscles beneath a bodybuilder's skin, and clinicians use
    structure and function, the hierarchy of structural organization,     it to locate appropriate blood vessels in which to feel pulses and
    and homeostasis--will unify and form the bedrock for your             draw blood.
    study of the human body. The final section of the chapter deals           Microscopic anatomy deals with structures too small to be
    with the language of anatomy--terminology that anatomists             seen with the naked eye. For most such studies, exceedingly
    use to describe the body or its parts.                                thin slices of body tissues are stained and mounted on glass
1                                                                         slides to be examined under the microscope. Subdivisions of
                                                                          microscopic anatomy include cytology (si-tolo-je), which con-
    An Overview of Anatomy                                                siders the cells of the body, and histology (his-tolo-je), the
                                                                          study of tissues.
    and Physiology                                                            Developmental anatomy traces structural changes that oc-
     Define anatomy and physiology and describe their                     cur in the body throughout the life span. Embryology (embre-
     subdivisions.                                                        olo-je), a subdivision of developmental anatomy, concerns
     Explain the principle of complementarity.                            developmental changes that occur before birth.
                                                                              Some highly specialized branches of anatomy are used pri-
    Two complementary branches of science--anatomy and                    marily for medical diagnosis and scientific research. For exam-
    physiology--provide the concepts that help us to understand           ple, pathological anatomy studies structural changes caused by
    the human body. Anatomy studies the structure of body parts           disease. Radiographic anatomy studies internal structures as
    and their relationships to one another. Anatomy has a certain         visualized by X-ray images or specialized scanning procedures.
    appeal because it is concrete. Body structures can be seen, felt,         Subjects of interest to anatomists range from easily seen
    and examined closely. You don't need to imagine what they             structures down to the smallest molecule. In molecular biol-
    look like.                                                            ogy, for example, the structure of biological molecules
       Physiology concerns the function of the body, in other words,      (chemical substances) is investigated. Molecular biology is
    how the body parts work and carry out their life-sustaining           actually a separate branch of biology, but it falls under the
    activities. When all is said and done, physiology is explainable      anatomy umbrella when we push anatomical studies to the
    only in terms of the underlying anatomy.                              subcellular level.
       To simplify the study of the body, when we refer to body               One essential tool for studying anatomy is a mastery of
    structures and/or physiological values (body temperature, heart       anatomical terminology. Others are observation, manipulation,
    rate, and the like), we will assume that we are talking about a       and, in a living person, palpation (feeling organs with your
    healthy young (22-year-old) male weighing about 155 lb (the           hands) and auscultation (listening to organ sounds with a
    reference man) or a healthy young female weighing about 125 lb        stethoscope). A simple example illustrates how some of these
    (the reference woman).                                                tools work together in an anatomical study.
                                                                              Let's assume that your topic is freely movable joints of the
                                                                          body. In the laboratory, you will be able to observe an animal
    Topics of Anatomy                                                     joint, noting how its parts fit together. You can work the joint
    Anatomy is a broad field with many subdivisions, each provid-         (manipulate it) to determine its range of motion. Using
    ing enough information to be a course in itself. Gross, or            anatomical terminology, you can name its parts and describe
    macroscopic, anatomy is the study of large body structures            how they are related so that other students (and your instruc-
    visible to the naked eye, such as the heart, lungs, and kidneys.      tor) will have no trouble understanding you. The list of word
    Indeed, the term anatomy (derived from the Greek words                roots (at the back of the book) and the glossary will help you
    meaning "to cut apart") relates most closely to gross anatomy         with this special vocabulary.
    because in such studies preserved animals or their organs are             Although you will make most of your observations with the
    dissected (cut up) to be examined.                                    naked eye or with the help of a microscope, medical technology
       Gross anatomy can be approached in different ways. In              has developed a number of sophisticated tools that can peer
    regional anatomy, all the structures (muscles, bones, blood ves-      into the body without disrupting it. Read about these exciting
    sels, nerves, etc.) in a particular region of the body, such as the   medical imaging techniques in A Closer Look on pp. 1819.
    abdomen or leg, are examined at the same time.
       In systemic anatomy (sis-temik),* body structure is studied        Topics of Physiology
    system by system. For example, when studying the cardiovascu-
    lar system, you would examine the heart and the blood vessels         Like anatomy, physiology has many subdivisions. Most of
    of the entire body.                                                   them consider the operation of specific organ systems. For ex-
                                                                          ample, renal physiology concerns kidney function and urine
    *For the pronunciation guide rules, see the Preface to the Student.
                                                                          production. Neurophysiology explains the workings of the
                                                                             Chapter 1 The Human Body: An Orientation                       3
nervous system. Cardiovascular physiology examines the op-           widely in size and shape, reflecting their unique functions in
eration of the heart and blood vessels. While anatomy provides       the body.
us with a static image of the body's architecture, physiology re-        The simplest living creatures are single cells, but in complex
veals the body's dynamic and animated workings.                      organisms such as human beings, the hierarchy continues on to
   Physiology often focuses on events at the cellular or mo-         the tissue level. Tissues are groups of similar cells that have a
lecular level. This is because the body's abilities depend on        common function. The four basic tissue types in the human
those of its individual cells, and cells' abilities ultimately de-   body are epithelium, muscle, connective tissue, and nervous
pend on the chemical reactions that go on within them.               tissue.
Physiology also rests on principles of physics, which help to            Each tissue type has a characteristic role in the body, which
explain electrical currents, blood pressure, and the way mus-        we explore in Chapter 4. Briefly, epithelium covers the body sur-          1
cles use bones to cause body movements, among other                  face and lines its cavities. Muscle provides movement. Connec-
things. We present basic chemical and physical principles in         tive tissue supports and protects body organs. Nervous tissue
Chapter 2 and throughout the book as needed to explain               provides a means of rapid internal communication by transmit-
physiological topics.                                                ting electrical impulses.
                                                                         An organ is a discrete structure composed of at least two tis-
                                                                     sue types (four is more common) that performs a specific
Complementarity of Structure and Function                            function for the body. The liver, the brain, and a blood vessel
Although it is possible to study anatomy and physiology indi-        are very different from the stomach, but each is an organ. You
vidually, they are really inseparable because function always re-    can think of each organ of the body as a specialized functional
flects structure. That is, what a structure can do depends on its    center responsible for a necessary activity that no other organ
specific form. This key concept is called the principle of com-      can perform.
plementarity of structure and function.                                  At the organ level, extremely complex functions become
   For example, bones can support and protect body organs be-        possible. Let's take the stomach for an example. Its lining is an
cause they contain hard mineral deposits. Blood flows in one di-     epithelium that produces digestive juices. The bulk of its wall is
rection through the heart because the heart has valves that          muscle, which churns and mixes stomach contents (food). Its
prevent backflow. Throughout this book, we accompany a de-           connective tissue reinforces the soft muscular walls. Its nerve
scription of a structure's anatomy with an explanation of its        fibers increase digestive activity by stimulating the muscle to
function, and we emphasize structural characteristics con-           contract more vigorously and the glands to secrete more diges-
tributing to that function.                                          tive juices.
                                                                         The next level of organization is the organ system level.
C H E C K Y O U R U N D E R S TA N D I N G                           Organs that work together to accomplish a common purpose
    1. In what way does physiology depend on anatomy?
                                                                     make up an organ system. For example, the heart and blood
    2. Would you be studying anatomy or physiology if you investi-
                                                                     vessels of the cardiovascular system circulate blood continu-
       gated how muscles shorten? If you explored the location of
                                                                     ously to carry oxygen and nutrients to all body cells. Besides
       the lungs in the body?
                                                                     the cardiovascular system, the other organ systems of the
                                                                     body are the integumentary, skeletal, muscular, nervous, en-
For answers, see Appendix G.                                         docrine, lymphatic, respiratory, digestive, urinary, and
                                                                     reproductive systems. (Note that the immune system is
                                                                     closely associated with the lymphatic system.) Look ahead to
                                                                     Figure 1.3 on pp. 6 and 7 for an overview of the 11 organ sys-
Levels of Structural Organization                                    tems, which we discuss in the next section and study in more
 Name the different levels of structural organization that           detail in Units 25.
 make up the human body, and explain their relationships.                The highest level of organization is the organism, the living
                                                                     human being. The organismal level represents the sum total of
 List the 11 organ systems of the body, identify their
                                                                     all structural levels working together to keep us alive.
 components, and briefly explain the major function(s) of
 each system.
                                                                     C H E C K Y O U R U N D E R S TA N D I N G

The human body has many levels of structural organization                3. What level of structural organization is typical of a cytolo-
(Figure 1.1). The simplest level of the structural hierarchy is             gist's field of study?
the chemical level, which we study in Chapter 2. At this level,          4. What is the correct structural order for the following terms:
atoms, tiny building blocks of matter, combine to form                      tissue, organism, organ, cell?
molecules such as water and proteins. Molecules, in turn, asso-          5. Which organ system includes the bones and cartilages?
ciate in specific ways to form organelles, basic components of              Which includes the nasal cavity, lungs, and trachea?
the microscopic cells. Cells are the smallest units of living        For answers, see Appendix G.
things. We examine the cellular level in Chapter 3. All cells
have some common functions, but individual cells vary
    4           U NI T 1 Organization of the Body

                                                                                          Organelle
        Atoms                          Molecule
                                                                                                             Smooth muscle cell




     1 Chemical level                                                     2 Cellular level
    Atoms combine to form molecules.                                     Cells are made up of molecules.
1
                                                                                                                            Smooth muscle tissue




                                                    Cardiovascular                         3 Tissue level
                                                    system
                                                                                          Tissues consist of similar types of cells.

                                                    Heart

                                                    Blood
                                                    vessels                                    Blood vessel (organ)

                                                                                                                                Smooth muscle tissue

                                                                                                                                   Connective tissue




                                                                                                      Epithelial
                                                                                                      tissue


                                                                                            4 Organ level
                                                                                           Organs are made up of different types of tissues.




     6 Organismal level                               5 Organ system level
    The human organism is made up of many            Organ systems consist of different
    organ systems.                                   organs that work together closely.

    Figure 1.1 Levels of structural organization. Components of the cardiovascular system are
    used to illustrate the levels of structural organization in a human being.




    Maintaining Life                                                             Like all complex animals, humans maintain their bound-
                                                                             aries, move, respond to environmental changes, take in and
     List the functional characteristics necessary to maintain life          digest nutrients, carry out metabolism, dispose of wastes, repro-
     in humans.                                                              duce themselves, and grow. We will introduce these necessary
     List the survival needs of the body.                                    life functions here and discuss them in more detail in later
                                                                             chapters.
                                                                                 We cannot emphasize too strongly that all body cells are in-
    Necessary Life Functions                                                 terdependent. This interdependence is due to the fact that
    Now that you know the structural levels of the human body, the           humans are multicellular organisms and our vital body func-
    question that naturally follows is: What does this highly orga-          tions are parceled out among different organ systems. Organ
    nized human body do?
                                                                            Chapter 1 The Human Body: An Orientation                            5
systems, in turn, work cooperatively to promote the well-being       Digestive system                                Respiratory system
                                                                     Takes in nutrients, breaks them                 Takes in oxygen and
of the entire body. This theme is repeated throughout the book.      down, and eliminates unabsorbed                 eliminates carbon dioxide
Figure 1.2 identifies some of the organ systems making major         matter (feces)
contributions to necessary life functions. Also, as you read this            Food                                       O2           CO2
section, check Figure 1.3 for more detailed descriptions of the
body's organ systems.
                                                                                         Cardiovascular system
                                                                                         Via the blood, distributes oxygen
Maintaining Boundaries                                                                   and nutrients to all body cells and
                                                                                         delivers wastes and carbon
Every living organism must maintain its boundaries so that its                           dioxide to disposal organs
internal environment (its inside) remains distinct from the ex-                                                                                     1
ternal environment surrounding it (its outside). In single-celled                                          Blood
organisms, the external boundary is a limiting membrane that                                                           CO2
encloses its contents and lets in needed substances while re-                                                         O2
stricting entry of potentially damaging or unnecessary sub-
stances. Similarly, all the cells of our body are surrounded by a
selectively permeable membrane.                                                                       Heart
                                                                                                                               Urinary system
   Additionally, the body as a whole is enclosed and protected                   Nutrients                                     Eliminates
by the integumentary system, or skin (Figure 1.3a). This system                                                                nitrogenous
protects our internal organs from drying out (a fatal change),                                                                 wastes and
                                                                                                Interstitial fluid             excess ions
bacteria, and the damaging effects of heat, sunlight, and an un-
believable number of chemicals in the external environment.

Movement
Movement includes the activities promoted by the muscular
system, such as propelling ourselves from one place to another
by running or swimming, and manipulating the external envi-                                  Nutrients and wastes pass
ronment with our nimble fingers (Figure 1.3c). The skeletal sys-                             between blood and cells
tem provides the bony framework that the muscles pull on as                                  via the interstitial fluid
they work (Figure 1.3b). Movement also occurs when sub-
stances such as blood, foodstuffs, and urine are propelled                                   Integumentary system
through internal organs of the cardiovascular, digestive, and                    Feces       Protects the body as a whole        Urine
urinary systems, respectively. On the cellular level, the muscle                             from the external environment
cell's ability to move by shortening is more precisely called
contractility.                                                       Figure 1.2 Examples of interrelationships among body organ
                                                                     systems.

Responsiveness
Responsiveness, or irritability, is the ability to sense changes
(which serve as stimuli) in the environment and then respond         amoeba, the cell itself is the "digestion factory," but in the multi-
to them. For example, if you cut your hand on broken glass, a        cellular human body, the digestive system performs this func-
withdrawal reflex occurs--you involuntarily pull your hand           tion for the entire body (Figure 1.3i).
away from the painful stimulus (the broken glass). You don't
have to think about it--it just happens! Likewise, when carbon       Metabolism
dioxide in your blood rises to dangerously high levels, chemical     Metabolism (me    -tabo-lizm; "a state of change") is a broad
sensors respond by sending messages to brain centers control-        term that includes all chemical reactions that occur within body
ling respiration, and you breathe more rapidly.                      cells. It includes breaking down substances into their simpler
   Because nerve cells are highly irritable and communicate          building blocks (more specifically, the process of catabolism),
rapidly with each other via electrical impulses, the nervous         synthesizing more complex cellular structures from simpler
system is most involved with responsiveness (Figure 1.3d).           substances (anabolism), and using nutrients and oxygen to pro-
However, all body cells are irritable to some extent.                duce (via cellular respiration) ATP, the energy-rich molecules
                                                                     that power cellular activities. Metabolism depends on the diges-
Digestion                                                            tive and respiratory systems to make nutrients and oxygen avail-
Digestion is the breaking down of ingested foodstuffs to simple      able to the blood and on the cardiovascular system to distribute
molecules that can be absorbed into the blood. The nutrient-         them throughout the body (Figure 1.3i, h, and f, respectively).
rich blood is then distributed to all body cells by the cardiovas-   Metabolism is regulated largely by hormones secreted by en-
cular system. In a simple, one-celled organism such as an            docrine system glands (Figure 1.3e).
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