4
UNIT ONE
1.2
ANATOMY AND PHYSIOLOGY
Two major areas of medical science,
anatomy
(ah-nat
o-me)
and
physiology
(F z
e-ol
o-je), address how the body main-
tains life. Anatomy, from the Greek for “a cutting up,” exam-
ines the
structures,
or morphology, of body parts—their
forms and organization. Physiology, from the Greek for “rela-
tionship to nature,” considers the
functions
of body parts—
what they do and how they do it. Although anatomists rely
more on examination of the body and physiologists more on
experimentation, together their efforts have provided a solid
foundation for understanding how our bodies work.
It is difF
cult to separate the topics of anatomy and phys-
iology because anatomical structures make possible their
functions. Parts form a well-organized unit—the
human
organism.
Each part contributes to the operation of the unit
as a whole. This functional role arises from the way the part
is constructed. ±or example, the arrangement of bones and
muscles in the human hand, with its long, jointed F
ngers,
makes grasping possible. The heart’s powerful muscular
walls contract and propel blood out of the chambers and
into blood vessels, and heart valves keep blood moving in
the proper direction. The shape of the mouth enables it to
receive food; tooth shapes enable teeth to break solid foods
into pieces; and the muscular tongue and cheeks are con-
structed in a way that helps mix food particles with saliva
and prepare them for swallowing
(f
g. 1.2)
.
As ancient as the F
elds of anatomy and physiology are,
we are always learning more. ±or example, researchers
recently used imaging technology to identify a previously
unrecognized part of the brain, the planum temporale, which
enables people to locate sounds in space. Many discoveries
today begin with investigations at the molecular or cellular
level. In this way, researchers have discovered that certain
cells in the small intestine bear the same taste receptor pro-
teins found on the tongue—at both locations, the receptors
detect the molecules that impart sweetness. The discovery of
the planum temporale is anatomical; the discovery of sweet
receptors in the intestine is physiological.
Many nuances of physiology are being revealed with
examination of the genes that function in particular cell
types under particular conditions, leading to sometimes
surprising F
ndings. Using such “gene expression proF
ling,”
for example, researchers discovered that after a spinal cord
injury, the damaged tissue releases a fl
ood of proteins pre-
viously associated only with skin wounds. ±inding these
proteins in the aftermath of spinal cord injury suggests new
drug targets.
PRACTICE
4
What are the dif
erences between anatomy and physiology?
5
Why is it diF
cult to separate the topics o± anatomy and physiology?
6
List several examples that illustrate how the structure o± a body
part makes possible its ±unction.
7
How are anatomy and physiology both old and new ²
elds?
1.3
LEVELS OF ORGANIZATION
Early investigators, limited in their ability to observe small
structures, such as cells and gene expression proF
les focused
their attention on larger body parts. Studies of small struc-
tures had to await invention of magnifying lenses and micro-
scopes, about 400 years ago. These tools revealed that larger
body structures were made up of smaller parts, which, in
turn, were composed of even smaller ones.
Today, scientists recognize that all materials, includ-
ing those that comprise the human body, are composed of
chemicals. Chemicals consist of tiny particles called
atoms,
composed of even smaller
subatomic particles;
atoms can
join to form larger
molecules;
small molecules may combine
to form larger molecules called
macromolecules.
In all organisms, including the human, the basic unit
of structure and function is a
cell.
Although individual cells
vary in size and shape, all share certain characteristics. Cells
of complex organisms such as humans contain structures
called
organelles
(or
gan-elz
) that carry on speciF c activi-
ties. Organelles are composed of assemblies of large mole-
cules, including proteins, carbohydrates, lipids, and nucleic
acids. Most human cells contain a complete set of genetic
instructions, yet use only a subset of them, allowing cells to
specialize. All cells share the same characteristics of life and
must meet certain requirements to stay alive.
Specialized cells assemble into layers or masses that
have speciF c functions. Such a group of cells forms a
tissue.
Groups of different tissues form
organs
—complex structures
with specialized functions—and groups of organs that func-
tion closely together comprise
organ systems.
Interacting
organ systems make up an
organism.
A body part can be described at different levels. The
heart, for example, consists of muscle, fat, and nervous tis-
sue. These tissues, in turn, are constructed of cells, which
contain organelles. All of the structures of life are, ultimately,
(a)
(b)
FIGURE 1.2
The structures o± body parts make possible their
±unctions: (
a
) The hand is adapted ±or grasping and (
b
) the mouth ±or
receiving ±ood. (Arrows indicate movements associated with these
±unctions.)
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