A. Chemical composition
Much information is available about the
chemical composition of the bodies of
animals and humans. The following data,
provided for illustrative purposes, apply to a
healthy, non-obese 70-kg adult man.
In addition to these macroelements, also
depicted in Figure 17-1, there are trace
quantities of magnesium, iron, manganese,
iodine, zinc, cobalt, copper, selenium,
molybdenum, fluorine, and many others.
It is important to appreciate that muscle
is the largest organ mass and that muscle,
along with the skeleton and adipose tissue,
make up about 75% of body weight
(Figure 17-2). It is not always recognized
that skin (the largest discrete organ) and
blood contribute as much as they do, or that
the brain and spinal cord are larger than any
of the visceral organs.
The dry weight of lipids in the body
represents about 10% of body weight, or 7
kg of a 70 kg adult. This leaves 63 kg as
(or nonfat) body weight. The term
is frequently used and it is of
particular importance in considerations of
growth and the efficiency of growth. The
nature and patterns of growth are described
in Chapters 55 and 59.
Oxygen is by far the
most abundant element in the body.
hydrogen and nitrogen make up about 97%of the body.
The remaining macroelements, a host of microelements,
and those present in only trace quantities are, however,
qualitatively very important.
The organ masses.
In adults, muscle is
usually the major organ system with adipose and skeleton
ranking second and third.
In animals selected for growth
rate and large mature size, adipose can become dominant
Note that the carcass – comprised of muscle,
adipose and parts of the skeleton – accounts for somewhat
less than the 75% shown here.
Of special importance now is that the water