Chemical elements in the body • Figure 2.2
The 26 elements in the human body fall into three categories:
major elements, lesser elements, and trace elements.
C h em ical Elem ents in the B ody
Major Elem ents
(96%
of total)
Oxygen (O)
■g
Carbon (C)
Hydrogen (H)
LD
Nitrogen (N)
0
10
20
30
40
50
60
70
Percent
Le sse r Elem ents
(3.6%
of total)
Calcium (Ca)
Phosphorus (P)
Potassium (K)
I
Sulfur (S)
.1
Sodium (Na)
LU
Chlorine (Cl)
Magnesium (Mg)
Iron (Fe)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Percent
Trace
Elem ents (total
0.4%)
Aluminum (Al), Boron (B), Chromium (Cr),
Cobalt (Co). Copper (Cu), Fluorine (F),
Iodine (I), Manganese (Mn), Molybdenum (Mo),
Selenium (Sel), Silicon (Si), Tin (Sn),
Vanadium (V), and Zinc (Zn)
tial energy and kinetic energy can be exchanged. Both
kinetic energy and potential energy can be classified as
other forms of energy, including the following:
M echanical
energy
is
energy directly involved
in
moving matter. For example, when you lift a box, you use
mechanical energy. Specifically, your muscles generate a
force to lift the box against the force of gravity.
C h e m ica l energy
is energy that is stored in the
chemical bonds of matter. For example, the wood for
a campfire stores energy in the bonds of its carbon-
containing molecules.
E le c tric a l energy
comes from moving positively or
negatively charged particles. For example, when you
plug a lamp into a wall outlet, negatively charged
electrons move through the lamp’s lightbulb. The
energy driving the flow of electrons is
electrical
energy.
R a d ia n t
energy
is
energy
from
the
electromagnetic spectrum
. Electromagnetic
radiation travels in waves.
The most common type of energy conversion that
you will see as you study anatomy and physiology
is the shift between chemical potential energy
and kinetic energy or heat energy. In your body,
you break down the chemical energy in food and
store it in other substances, such as adenosine triphosphate
(ATP), carbohydrates, and fats. The processes that convert
energy from one form to another are not 100% efficient, so
some energy is lost as heat energy. It is the heat energy lost
from the chemical reactions in your body that keeps your
body temperature above that of its surroundings.
Matter Is Made of Chemical Elements
Matter is made of building blocks called
chem ical elements
.
Chemical elements are substances that cannot be broken
down into any simpler units by chemical means and still re-
tain the same chemical properties. There are 117 different
chemical elements; 94 occur in nature, and 23 are synthetic.
Only 26 of the chemical elements are normally present in the
human body (
Figure 2 .2
). Each element is represented by
a one- or two-letter symbol representing the element’s
name, usually an English or Latin name or a name rep-
resenting a famous scientist. For example, C
is carbon, H is hydrogen, O is oxygen, N is
nitrogen, P is phosphorus, Ca is calcium, and
Na, which comes from the Latin word
natrium,
is sodium. Figure 2.2 shows the organization
of the elements in the human body into three
categories: major (96%), lesser (3.6%), and
trace (0.4%). The chemical symbol of each
element is also given.
electrom agnetic
spectrum
The distri-
bution of frequencies
of light, including
gamma rays, X-rays,
ultraviolet light, visible
light, microwaves, and
radio waves.
Matter Is Made of Elements and Atoms 23
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