Introduction to Human Anatomy and Physiology
refers to substances that provide organisms with
necessary chemicals (nutrients) in addition to water.
Nutrients supply energy and raw materials for building
new living matter.
is a gas that makes up about one-F
fth of the air.
It is used to release energy from nutrients. The energy,
in turn, is used to drive metabolic processes.
is a form of energy present in our environment.
It is also a product of metabolic reactions, and it
partly controls the rate at which these reactions occur.
Generally, the more heat, the more rapidly chemical
reactions take place.
is a measure of the
amount of heat present.
With the exception of an organism’s reproductive system,
which perpetuates the species, all body structures and func-
tions work in ways that maintain life.
Requirements of Organisms
Human life depends upon the following environmental factors:
is the most abundant substance in the body. It
is required for a variety of metabolic processes, and it
provides the environment in which most of them take
place. Water also transports substances in organisms
and is important in regulating body temperature.
The device continues to produce data, painting
portraits of Michael’s brain from diF
erent angles.
Michael and his parents nervously wait two
days for the expert eyes of a radiologist to inter-
The magnet generates a magnetic ±
eld that
alters the alignment and spin of certain types of
atoms within Michael’s brain. At the same time, a
second rotating magnetic field causes particular
types of atoms (such as the hydrogen atoms in
body fluids and organic compounds) to release
weak radio waves with characteristic frequencies.
The nearby antenna receives and amplifies the
radio waves, which are then processed by a com-
puter. Within a few minutes, the computer gener-
ates a sectional image based on the locations and
concentrations of the atoms being studied (±
g. 1C).
pret the MR scan. Happily, the scan shows normal
brain structure. Whatever is causing Michael’s
headaches, it is not a brain tumor—at least not
one large enough to be imaged.
²alsely colored MR image of a human head and brain (sagittal section,
see ±
g. 1.21).
This image resulting from an
ultrasonographic procedure reveals a fetus in the uterus.
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