4
UNIT 1
Organization of the Body
1
Maintaining Life
List the functional characteristics necessary to maintain life
in humans.
List the survival needs of the body.
Necessary Life Functions
Now that you know the structural levels of the human body, the
question that naturally follows is: What does this highly orga-
nized human body do?
Like all complex animals, humans maintain their bounda-
ries, move, respond to environmental changes, take in and
digest nutrients, carry out metabolism, dispose of wastes, re-
produce themselves, and grow. We will introduce these nec-
essary life functions here and discuss them in more detail in
later chapters.
We cannot emphasize too strongly that all body cells are
interdependent. Tis interdependence is due to the fact that
humans are multicellular organisms and our vital body func-
tions are parceled out among diļ¬€erent organ systems. Organ
systems, in turn, work cooperatively to promote the well-being
Chemical level
Atoms combine to form molecules.
Cellular level
Cells are made up of molecules.
Tissue level
Tissues consist of similar types of cells.
Organ level
Organs are made up of different types of tissues.
Organ system level
Organ systems consist of different
organs that work together closely.
Organismal level
The human organism is made up of many
organ systems.
Cardiovascular
system
Organelle
Molecule
Atoms
Smooth muscle cell
Smooth muscle tissue
Connective tissue
Blood vessel (organ)
Heart
Blood
vessels
Epithelial
tissue
Smooth muscle tissue
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.
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