Aging and Disease Upset Homeostasis
Aging represents a progressive decline in the body’s ho-
meostatic mechanisms. Some components of feedback
mechanisms may weaken or fail. For example, as we age,
arterial walls become stiffer. As a result, the barorecep-
tors (see Figure 1.4) in certain arteries become less able
to sense increases or decreases in blood pressure. Further-
more, the heart muscle becomes stiffer and weaker, and it
becomes less able to increase the force of contraction to
increase blood pressure.
Similarly, disease may alter the body’s ability to re-
spond to various stimuli, affecting components of feedback
systems. For example, ovarian cancer may cause an ovary
to secrete too much of the female sex hormone estrogen.
The increased estrogen in the blood is communicated to
the pituitary gland and hypothalamus, which depress the
secretions of three other hormones that help maintain
normal functioning of the ovaries and signal ovulation.
Because their secretions are depressed, ovulation does not
occur, and the woman becomes infertile.
CONCEPT CHECK
1.
What
are two examples of reproduction in the
human body?
2.
How
do negative and positive feedback sys-
tems differ from one another?
3.
How
would age affect the response by the neg-
ative feedback system to an increase in blood
pressure? (Keep in mind that age alters the abil-
ity of the heart to change its rate of beating.)
Anatomical Road Maps Guide
Navigation Through the Body
LEARNING OBJECTIVES
1.
Identify
major regions of the body and relate
their common names to the corresponding ana-
tomical terms for various body parts.
2.
Define
the directional terms and the anatomical
planes and sections used to locate parts of the
human body.
3.
Describe
the principal body cavities and the
organs they contain.
f you ask someone for directions to some
place in a city, you might get a response like,
“Go two blocks north to Main Street, take
a right, and proceed 0.5 miles.” Scientists
need to describe locations and directions on the human
body in a similarly clinical fashion to avoid misinterpre-
tation. For example, how would you describe a cut on
your forearm? You might say that it is 2 cm above the
right elbow. But does “above the elbow” mean toward
the wrist or toward the shoulder? Anatomists have de-
vised a system of terms and directions for naming vari-
ous body parts and locating them precisely. How does
this system work?
The Body Can Be Divided
into Specific Anatomical Regions
Descriptions of any part of the
human
body
assume
that
the
body is in a specific stance called
the
anatomical position
(
Figure
1.5
). In the anatomical position,
the body is upright; however, two
terms describe a reclining body.
If the body is lying face down, it
is in the
p ro n e
position. If the
body is lying face up, it is in the
su p in e
position. The face view of
the body is called the
a n te rio r
side, or
ve n tra l
side, and
the back view is called the
p o ste rio r
side, or
d o rsa l
side.
The body is further divided into the following major
regions:
Head (cephalic)
—Skull and face
Neck (cervical)
—Supports head and attaches it to trunk
Trunk (tthoracic, abdominal, pelvic)
—Chest, back, abdomen,
pelvis, and buttock
Upper limb
—Shoulder, armpit, arm, forearm, wrist, and
hand
Lower limb
—Buttock, thigh, leg, ankle, and foot
anatomical posi-
tion
(an-a-TOM-i-kal)
The subject stands
erect with the head
level, eyes facing
forward, feet flat on
the floor, and directed
forward, and arms
at the sides, with the
palms turned forward.
10 CHAPTER 1
Organization of the Human Body
previous page 45 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online next page 47 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online Home Toggle text on/off