6
UNIT 1
Organization of the Body
1
Several organ systems participate in excretion. For example,
the digestive system rids the body of indigestible food residues
in feces, and the urinary system disposes of nitrogen-containing
metabolic wastes, such as urea, in urine (Figure 1.3i and j). Car-
bon dioxide, a by-product of cellular respiration, is carried in
Excretion
Excretion
is the process of removing wastes, or
excreta
(ek-
skre
9
tah), from the body. If the body is to operate as we expect
it to, it must get rid of nonuseful substances produced during
digestion and metabolism.
(a) Integumentary System
Forms the external body covering, and
protects deeper tissues from injury.
Synthesizes vitamin D, and houses
cutaneous (pain, pressure, etc.) receptors
and sweat and oil glands.
Nails
Skin
Hair
(b) Skeletal System
Protects and supports body organs, and
provides a framework the muscles use
to cause movement. Blood cells are
formed within bones. Bones store minerals.
Bones
Joint
(c) Muscular System
Allows manipulation of the environment,
locomotion, and facial expression. Main-
tains posture, and produces heat.
Skeletal
muscles
(d) Nervous System
As the fast-acting control system of the
body, it responds to internal and external
changes by activating appropriate
muscles and glands.
Brain
Nerves
Spinal
cord
(e) Endocrine System
Glands secrete hormones that regulate
processes such as growth, reproduction,
and nutrient use (metabolism) by body
cells.
Pineal gland
Pituitary
gland
Thyroid
gland
Thymus
Adrenal
gland
Pancreas
Testis
Ovary
(f)
Cardiovascular System
Blood vessels transport blood, which
carries oxygen, carbon dioxide,
nutrients, wastes, etc. The heart pumps
blood.
Heart
Blood
vessels
Figure 1.3
The body’s organ systems and their major functions.
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