The Human Body: An Orientation
The Language of Anatomy
Anatomical Position and Directional Terms
In the anatomical position, the body is erect, facing forward, feet
slightly apart, arms at sides with palms forward.
Directional terms allow body parts to be located precisely. Terms
that describe body directions and orientation include: superior/
inferior; anterior/posterior; ventral/dorsal; medial/lateral;
intermediate; proximal/distal; and superﬁcial/deep.
Regional terms are used to designate speciﬁc areas of the body
(see Figure 1.7).
People vary internally as well as externally, but extreme variations
Body Planes and Sections
±e body or its organs may be cut along planes, or imaginary
lines, to produce diﬀerent types of sections. Frequently used
planes are sagittal, frontal, and transverse.
Body Cavities and Membranes
±e body contains two major closed cavities. ±e dorsal cavity,
subdivided into the cranial and spinal cavities, contains the
brain and spinal cord. ±e ventral cavity is subdivided into
the thoracic cavity, which houses the heart and lungs, and the
abdominopelvic cavity, which contains the liver, digestive organs,
and reproductive structures.
±e walls of the ventral cavity and the surfaces of the organs
it contains are covered with thin membranes, the parietal and
visceral serosae, respectively. ±e serosae produce a thin ﬂuid that
decreases friction during organ functioning.
±e abdominopelvic cavity may be divided by four planes
into nine abdominopelvic regions (epigastric, umbilical,
hypogastric, right and le² iliac, right and le² lumbar, and
right and le² hypochondriac), or by two planes into four
quadrants. (For boundaries and organs contained, see
Figures 1.11 and 1.12.)
±ere are several smaller body cavities. Most of these are in the
head and open to the exterior.
Levels of Structural Organization
±e levels of structural organization of the body, from simplest to
most complex, are: chemical, cellular, tissue, organ, organ system,
±e 11 organ systems of the body are the integumentary,
skeletal, muscular, nervous, endocrine, cardiovascular,
lymphatic, respiratory, digestive, urinary, and reproductive
systems. ±e immune system is a functional system closely
associated with the lymphatic system. (For functions of these
systems see pp. 6–7.)
Necessary Life Functions
All living organisms carry out certain vital functional activities
necessary for life, including maintenance of boundaries,
movement, responsiveness, digestion, metabolism, excretion,
reproduction, and growth.
Survival needs include nutrients, water, oxygen, and appropriate
temperature and atmospheric pressure.
Homeostasis is a dynamic equilibrium of the internal
environment. All body systems contribute to homeostasis, but the
nervous and endocrine systems are most important. Homeostasis
is necessary for health.
Control mechanisms of the body contain at least three elements
that work together: receptor(s), control center, and eﬀector(s).
Negative feedback mechanisms reduce the eﬀect of the original
stimulus, and are essential for maintaining homeostasis. Body
temperature, heart rate, breathing rate and depth, and blood
levels of glucose and certain ions are regulated by negative
Positive feedback mechanisms intensify the initial stimulus,
leading to an enhancement of the response. ±ey rarely
contribute to homeostasis, but blood clotting and labor
contractions are regulated by such mechanisms.
With age, the eﬃciency of negative feedback mechanisms
declines, and positive feedback mechanisms occur more
frequently. ±ese changes underlie certain disease conditions.
(Some questions have more than one correct answer. Select the best
answer or answers from the choices given.)
±e correct sequence of levels forming the structural hierarchy is
organ, organ system, cellular, chemical, tissue, organismal;
chemical, cellular, tissue, organismal, organ, organ system;
chemical, cellular, tissue, organ, organ system, organismal;
organismal, organ system, organ, tissue, cellular, chemical.
±e structural and functional unit of life is
Which of the following is a
functional characteristic of
all of these.
Two of these organ systems bear the
for ensuring homeostasis of the internal environment.
In (a)–(e), a directional term [e.g., distal in (a)] is followed by
terms indicating diﬀerent body structures or locations (e.g., the