16
UNIT ONE
Integration and Coordination
For the body to act as a unit, its parts must be integrated and
coordinated. The nervous and endocrine systems control and
adjust various organ functions from time to time, maintain-
ing homeostasis.
The
nervous
(ner
vus)
system
(f
g. 1.15)
consists of
the brain, spinal cord, nerves, and sense organs. Nerve
cells within these organs use electrochemical signals called
nerve impulses
(action potentials) to communicate with
one another and with muscles and glands. Each impulse
produces a relatively short-term effect on its target. Some
nerve cells act as specialized sensory receptors that can
detect changes occurring inside and outside the body. Other
nerve cells receive the impulses transmitted from these sen-
sory units and interpret and act on the information. Still
other nerve cells carry impulses from the brain or spinal
cord to muscles or glands, stimulating them to contract or
to secrete products. Chapters 10 and 11 discuss the nervous
system, and chapter 12 discusses sense organs.
The
endocrine
(en
do-krin)
system
g. 1.15) includes
all the glands that secrete chemical messengers, called
hor-
mones.
Hormones, in turn, travel away from the glands in
body fl
uids such as blood or tissue fl
uid. Usually a particu-
lar hormone affects only a particular group of cells, called
its
target cells.
The effect of a hormone is to alter the metab-
olism of the target cells. Compared to nerve impulses, hor-
monal effects occur over a relatively long period.
Organs of the endocrine system include the pituitary,
thyroid, parathyroid, and adrenal glands, as well as the
pancreas, ovaries, testes, pineal gland, and thymus. These
are discussed further in chapter 13.
Transport
Two organ systems transport substances throughout the
internal environment. The
cardiovascular
(kahr
de-o-
vas
ku-lur)
system
(f
g. 1.16)
includes the heart, arteries,
capillaries, veins, and blood. The heart is a muscular pump
that helps force blood through the blood vessels. Blood trans-
ports gases, nutrients, hormones, and wastes. It carries oxy-
gen from the lungs and nutrients from the digestive organs to
all body cells, where these substances are used in metabolic
processes. Blood also transports hormones from endocrine
glands to their target cells and carries wastes from body cells
to the excretory organs, where the wastes are removed from
the blood and released to the outside. Blood and the cardio-
vascular system are discussed in chapters 14 and 15.
The
lymphatic
(lim-fat
ik)
system
(± g. 1.16) is sometimes
considered part of the cardiovascular system. It is composed
of the lymphatic vessels, lymph fl uid, lymph nodes, thymus,
and spleen. This system transports some of the fluid from
the spaces in tissues (tissue fl uid) back to the bloodstream
and carries certain fatty substances away from the digestive
organs. Cells of the lymphatic system, called lymphocytes,
defend the body against infections by removing pathogens
Integumentary system
FIGURE 1.13
The integumentary system covers the body.
FIGURE 1.14
The skeletal and muscular systems provide support
and movement.
Skeletal system
Muscular system
previous page 46 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 48 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off