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Organization and General
Plan of the Body

Levels of Organization
Chemicals
Cells
Tissues
Organs
Organ Systems
Metabolism and Homeostasis
Terminology and General Plan of the Body
Body Parts and Areas
Terms of Location and Position
Body Cavities and Their Membranes
Dorsal cavity
Ventral cavity
Planes and Sections
Areas of the Abdomen
BOX 1–1 REPLACING TISSUES AND ORGANS
BOX 1–2 VISUALIZING THE INTERIOR OF THE BODY
Student Objectives
• Define the terms anatomy, physiology, and pathophysiology.
Use an example to explain how they are
related.
• Name the levels of organization of the body from
simplest to most complex, and explain each.
• Define the terms metabolism, metabolic rate, and
homeostasis, and use examples to explain.
• Explain how a negative feedback mechanism
works, and how a positive feedback mechanism
differs.
• Describe the anatomic position.
• State the anatomic terms for the parts of the body.
• Use proper terminology to describe the location
of body parts with respect to one another.
• Name the body cavities, their membranes, and
some organs within each cavity.
• Describe the possible sections through the body or
an organ.
• Explain how and why the abdomen is divided into
smaller areas. Be able to name organs in these
areas.
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Organization and General
Plan of the Body
3
New Terminology
Anatomy (uh-NAT-uh-mee)
Body cavity (BAH-dee KAV-i-tee)
Cell (SELL)
Homeostasis (HOH-me-oh-STAY-sis)
Inorganic chemicals (IN-or-GAN-ik KEM-i-kuls)
Meninges (me-NIN-jeez)
Metabolism (muh-TAB-uh-lizm)
Negative feedback (NEG-ah-tiv FEED-bak)
Organ (OR-gan)
Organ system (OR-gan SIS-tem)
Organic chemicals (or-GAN-ik KEM-i-kuls)
Pathophysiology (PATH-oh-FIZZ-ee-AH-luh-jee)
Pericardial membranes (PER-ee-KAR-dee-uhl
MEM-brayns)
Peritoneum/Mesentery (PER-i-toh-NEE-um/MEZen-
TER-ee)
Physiology (FIZZ-ee-AH-luh-jee)
Plane (PLAYN)
Pleural membranes (PLOOR-uhl MEM-brayns)
Positive feedback (PAHS-ah-tiv FEED-bak)
Section (SEK-shun)
Tissue (TISH-yoo)
Related Clinical Terminology
Computed tomography (CT) scan
(kom-PEW-ted toh-MAH-grah-fee SKAN)
Diagnosis (DYE-ag-NO-sis)
Disease (di-ZEEZ)
Magnetic resonance imaging (MRI)
(mag-NET-ik REZ-ah-nanse IM-ah-jing)
Positron emission tomography (PET)
(PAHZ-i-tron e-MISH-un toh-MAH-grah-fee)
Terms that appear in bold type in the chapter text are defined in the glossary, which begins on page 547.
The human body is a precisely structured container
of chemical reactions. Have you ever thought of yourself
in this way? Probably not, and yet, in the strictly
physical sense, that is what each of us is. The body
consists of trillions of atoms in specific arrangements
and thousands of chemical reactions proceeding in
a very orderly manner. That literally describes
us, and yet it is clearly not the whole story. The keys
to understanding human consciousness and selfawareness
are still beyond our grasp. We do not yet
know what enables us to study ourselves—no other
animals do, as far as we know—but we have accumulated
a great deal of knowledge about what we are
made of and how it all works. Some of this knowledge
makes up the course you are about to take, a course in
basic human anatomy and physiology.
Anatomy is the study of body structure, which
includes size, shape, composition, and perhaps even
coloration. Physiology is the study of how the body
functions. The physiology of red blood cells, for example,
includes what these cells do, how they do it, and
how this is related to the functioning of the rest of the
body. Physiology is directly related to anatomy. For
example, red blood cells contain the mineral iron in
molecules of the protein called hemoglobin; this is an
aspect of their anatomy. The presence of iron enables
red blood cells to carry oxygen, which is their function.
All cells in the body must receive oxygen in order to
function properly, so the physiology of red blood cells
is essential to the physiology of the body as a whole.
Pathophysiology is the study of disorders of functioning,
and a knowledge of normal physiology makes
such disorders easier to understand. For example, you
are probably familiar with the anemia called irondeficiency
anemia. With insufficient iron in the diet,
there will not be enough iron in the hemoglobin of
red blood cells, and hence less oxygen will be transported
throughout the body, resulting in the symptoms
of the iron-deficiency disorder. This example
shows the relationship between anatomy, physiology,
and pathophysiology.
The purpose of this text is to enable you to gain
an understanding of anatomy and physiology with
the emphasis on normal structure and function. Many
examples of pathophysiology have been included,
however, to illustrate the relationship of disease to
normal physiology and to describe some of the procedures
used in the diagnosis of disease. Many of the
examples are clinical applications that will help you
begin to apply what you have learned and demonstrate
that your knowledge of anatomy and physiology will
become the basis for your further study in the health
professions.
LEVELS OF ORGANIZATION
The human body is organized into structural and
functional levels of increasing complexity. Each higher
level incorporates the structures and functions of the
previous level, as you will see. We will begin with the
simplest level, which is the chemical level, and proceed
to cells, tissues, organs, and organ systems. All of
the levels of organization are depicted in Fig. 1–1.
CHEMICALS
The chemicals that make up the body may be divided
into two major categories: inorganic and organic.
Inorganic chemicals are usually simple molecules
made of one or two elements other than carbon (with
a few exceptions). Examples of inorganic chemicals are
water (H2O); oxygen (O2); one of the exceptions, carbon
dioxide (CO2); and minerals such as iron (Fe), calcium
(Ca), and sodium (Na). Organic chemicals are
often very complex and always contain the elements
carbon and hydrogen. In this category of organic
chemicals are carbohydrates, fats, proteins, and
nucleic acids. The chemical organization of the body
is the subject of Chapter 2.
CELLS
The smallest living units of structure and function are
cells. There are many different types of human cells,
though they all have certain similarities. Each type of
cell is made of chemicals and carries out specific
chemical reactions. Cell structure and function are
discussed in Chapter 3.
TISSUES
A tissue is a group of cells with similar structure and
function. There are four groups of tissues:
Epithelial tissues—cover or line body surfaces; some
are capable of producing secretions with specific
functions. The outer layer of the skin and sweat
glands are examples of epithelial tissues. Internal
epithelial tissues include the walls of capillaries
(squamous epithelium) and the kidney tubules
(cuboidal epithelium), as shown in Fig. 1–1.
4 Organization and General Plan of the Body
1. Chemical Level
2. Cellular Level
3. Tissue Level
4. Organ Level
5. Organ System
Level
6. Organism Level
Cuboidal epithelium
Squamous epithelium
Smooth muscle
Kidney
Urinary
bladder
Urinary
system
Figure 1–1. Levels of structural organization of the human body, depicted from the
simplest (chemical) to the most complex (organism). The organ system shown here is the
urinary system.
QUESTION: What other organ system seems to work directly with the urinary system?
5
Connective tissues—connect and support parts of
the body; some transport or store materials. Blood,
bone, cartilage, and adipose tissue are examples of
this group.
Muscle tissues—specialized for contraction, which
brings about movement. Our skeletal muscles and
the heart are examples of muscle tissue. In Fig. 1–1,
you see smooth muscle tissue, which is found in
organs such as the urinary bladder and stomach.
Nerve tissue—specialized to generate and transmit
electrochemical impulses that regulate body functions.
The brain and optic nerves are examples of
nerve tissue.
The types of tissues in these four groups, as well as
their specific functions, are the subject of Chapter 4.
ORGANS
An organ is a group of tissues precisely arranged so as
to accomplish specific functions. Examples of organs
are the kidneys, individual bones, the liver, lungs,
and stomach. The kidneys contain several kinds of
epithelial, or surface tissues, for their work of absorption.
The stomach is lined with epithelial tissue that
secretes gastric juice for digestion. Smooth muscle
tissue in the wall of the stomach contracts to mix
food with gastric juice and propel it to the small intestine.
Nerve tissue carries impulses that increase or
decrease the contractions of the stomach (see Box 1–1:
Replacing Tissues and Organs).
ORGAN SYSTEMS
An organ system is a group of organs that all contribute
to a particular function. Examples are the urinary
system, digestive system, and respiratory system.
In Fig. 1–1 you see the urinary system, which consists
of the kidneys, ureters, urinary bladder, and urethra.
These organs all contribute to the formation and
elimination of urine.
As a starting point, Table 1–1 lists the organ systems
of the human body with their general functions,
and some representative organs, and Fig. 1–2 depicts
6 Organization and General Plan of the Body
BOX 1–1 REPLACING TISSUES AND ORGANS
eventually be used to cover a large surface. Other
cells grown in culture include cartilage, bone, pancreas,
and liver. Much research is being done on
liver implants (not transplants), clusters of functional
liver cells grown in a lab. Such implants
would reduce or eliminate the need for human
donors. Tissue engineering is also being used to create
arteries and urinary bladders.
Many artificial replacement parts have also been
developed. These are made of plastic or metal and
are not rejected as foreign by the recipient’s
immune system. Damaged heart valves, for example,
may be replaced by artificial ones, and sections
of arteries may be replaced by tubular grafts made
of synthetic materials. Artificial joints are available
for every joint in the body, as is artificial bone for
reconstructive surgery. Cochlear implants are tiny
instruments that convert sound waves to electrical
impulses the brain can learn to interpret, and have
provided some sense of hearing for people with certain
types of deafness. Work is also progressing on
the use of a featherweight computer chip as an artificial
retina, on devices that help damaged hearts
pump blood more efficiently, and on small, selfcontained
artificial hearts.
Blood transfusions are probably the most familiar
and frequent form of “replacement parts” for people.
Blood is a tissue, and when properly typed and
cross-matched (blood types will be discussed in
Chapter 11) may safely be given to someone with
the same or a compatible blood type.
Organs, however, are much more complex structures.
When a patient receives an organ transplant,
there is always the possibility of rejection (destruction)
of the organ by the recipient’s immune system
(Chapter 14). With the discovery and use of
more effective immune-suppressing medications,
however, the success rate for many types of organ
transplants has increased. Organs that may be transplanted
include corneas, kidneys, the heart, the
liver, and the lungs.
The skin is also an organ, but skin transplanted
from another person will not survive very long.
Several kinds of artificial skin are now available to
temporarily cover large areas of damaged skin.
Patients with severe burns, for example, will eventually
need skin grafts from their own unburned
skin to form permanent new skin over the burn
sites. It is possible to “grow” a patient’s skin in laboratory
culture, so that a small patch of skin may
all of the organ systems. Some organs are part of two
organ systems; the pancreas, for example, is both a
digestive and an endocrine organ, and the diaphragm
is part of both the muscular and respiratory systems.
All of the organ systems make up an individual person.
The balance of this text discusses each system in more
detail.
METABOLISM AND HOMEOSTASIS
Metabolism is a collective noun; it is all of the chemical
reactions and physical processes that take place
within the body. Metabolism includes growing, repairing,
reacting, and reproducing—all the characteristics
of life. The pumping of the heart, the digestion of
food in the stomach, the diffusion of gases in the lungs
and tissues, and the production of energy in each cell
of the body are just a few of the thousands of aspects
of metabolism. Metabolism comes from a Greek word
meaning “change,” and the body is always changing in
visible ways (walking down the street), microscopic
ways (cells dividing in the skin to produce new epidermis),
and submicroscopic or molecular ways (RNA
and enzymes constructing new proteins). A related
concept, metabolic rate, is most often used to mean
the speed at which the body produces energy and heat,
or, put another way, energy production per unit of
time, such as 24 hours. Metabolic rate, therefore, is
one aspect of metabolism.
Organization and General Plan of the Body 7
Table 1–1 THE ORGAN SYSTEMS
System Functions Organs*
Integumentary
Skeletal
Muscular
Nervous
Endocrine
Circulatory
Lymphatic
Respiratory
Digestive
Urinary
Reproductive
*These are simply representative organs, not an all-inclusive list.
• Is a barrier to pathogens and chemicals
• Prevents excessive water loss
• Supports the body
• Protects internal organs and red bone marrow
• Provides a framework to be moved by muscles
• Moves the skeleton
• Produces heat
• Interprets sensory information
• Regulates body functions such as movement by means
of electrochemical impulses
• Regulates body functions such as growth and reproduction
by means of hormones
• Regulates day-to-day metabolism by means of hormones
• Transports oxygen and nutrients to tissues and removes
waste products
• Returns tissue fluid to the blood
• Destroys pathogens that enter the body and provides
immunity
• Exchanges oxygen and carbon dioxide between the air
and blood
• Changes food to simple chemicals that can be absorbed
and used by the body
• Removes waste products from the blood
• Regulates volume and pH of blood and tissue fluid
• Produces eggs or sperm
• In women, provides a site for the developing
embryo-fetus
skin, subcutaneous tissue
bones, ligaments
muscles, tendons
brain, nerves, eyes, ears
thyroid gland, pituitary
gland, pancreas
heart, blood, arteries
spleen, lymph nodes
lungs, trachea, larynx,
diaphragm
stomach, colon, liver,
pancreas
kidneys, urinary bladder,
urethra
Female: ovaries, uterus
Male: testes, prostate gland
Circulatory system
Skeletal
system
Integumentary
system
Muscular
system
Nervous
system
Figure 1–2. Organ systems. Compare the depiction of each system to its description in
Table 1–1.
QUESTION: Name at least one organ shown in each system.
8
Respiratory
system
Urinary system Endocrine system
Digestive
system
Lymphatic system
Reproductive system
Figure 1–2. (Continued)
9
A person who is in good health may be said to be in
a state of homeostasis. Homeostasis reflects the ability
of the body to maintain a relatively stable metabolism
and to function normally despite many constant
changes. The changes that are part of normal metabolism
may be internal or external, and the body must
respond appropriately.
Eating breakfast, for example, brings about an
internal change. Suddenly there is food in the stomach,
and something must be done with it. What happens?
The food is digested or broken down into
simple chemicals that the body can use. The protein in
a hard-boiled egg is digested into amino acids, its basic
chemical building blocks; these amino acids can then
be used by the cells of the body to produce their own
specialized proteins.
An example of an external change is a rise in environmental
temperature. On a hot day, the body temperature
would also tend to rise. However, body
temperature must be kept within its normal range of
about 97 to 99 F (36 to 38 C) in order to support
normal functioning. What happens? One of the body’s
responses to the external temperature rise is to
increase sweating so that excess body heat can be lost
by the evaporation of sweat on the surface of the skin.
This response, however, may bring about an undesirable
internal change, dehydration. What happens? As
body water decreases, we feel the sensation of thirst
and drink fluids to replace the water lost in sweating.
Notice that when certain body responses occur, they
reverse the event that triggered them. In the preceding
example a rising body temperature stimulates
increased sweating, which lowers body temperature,
which in turn decreases sweating. Unnecessary sweating
that would be wasteful of water is prevented. This
is an example of a negative feedback mechanism, in
which the body’s response reverses the stimulus (in
effect, turning it off for a while) and keeps some aspect
of the body metabolism within its normal range.
Look at Fig. 1–3 for another negative feedback
mechanism, one in which the hormone thyroxine regulates
the metabolic rate of the body. As metabolic
rate decreases, the hypothalamus (part of the brain)
and pituitary gland detect this decrease and secrete
hormones to stimulate the thyroid gland (on the front
of the neck just below the larynx) to secrete the hormone
thyroxine. Thyroxine stimulates the cellular
enzyme systems that produce energy from food, which
increases the metabolic rate. The rise in energy and
heat production is detected by the brain and pituitary
gland. They then decrease secretion of their hormones,
which in turn inhibits any further secretion of
thyroxine until the metabolic rate decreases again.
Metabolic rate does rise and fall, but is kept within
normal limits.
You may be wondering if there is such a thing as a
positive feedback mechanism. There is, but they are
rare in the body and quite different from a negative
feedback mechanism. In a positive feedback mechanism,
the response to the stimulus does not stop or
reverse the stimulus, but instead keeps the sequence of
events going. A good example is childbirth, in which
the sequence of events, simply stated, is as follows:
Stretching of the uterine cervix stimulates secretion of
the hormone oxytocin by the posterior pituitary gland.
Oxytocin stimulates contraction of the uterine muscle,
which causes more stretching, which stimulates more
oxytocin and, hence, more contractions. The mechanism
stops with the delivery of the baby and the placenta.
This is the “brake,” the interrupting event.
Any positive feedback mechanism requires an
external “brake,” something to interrupt it. Blood
clotting is such a mechanism, and without external
controls, clotting may become a vicious cycle of clotting
and more clotting, doing far more harm than
good (discussed in Chapter 11). Inflammation following
an injury is beneficial and necessary for repair to
begin, but the process may evolve into a cycle of damage
and more damage. The rise of a fever may also
trigger a positive feedback mechanism. Notice in Fig.
1–3 that bacteria have affected the body’s thermostat
in the hypothalamus and caused a fever. The rising
body temperature increases the metabolic rate, which
increases body temperature even more, becoming a
cycle. Where is the inhibition, the brake? For this
infection, the brake is white blood cells destroying the
bacteria that caused the fever. An interruption from
outside the cycle is necessary. It is for this reason,
because positive feedback mechanisms have the potential
to be self-perpetuating and cause harm, that they
are rare in the body.
Negative feedback mechanisms, however, contain
their own brakes in that inhibition is a natural part of
the cycle, and the body has many of them. The secretion
of most hormones (Chapter 10) is regulated by
negative feedback mechanisms. The regulation of
heart rate (Chapter 12) and blood pressure (Chapter
13) involves several negative feedback mechanisms.
10 Organization and General Plan of the Body
The result of all of these mechanisms working together
is that all aspects of body functioning, that is, of
metabolism, are kept within normal limits, a steady
state or equilibrium. This is homeostasis.
In the chapters to come, you will find many more
examples of homeostasis. As you continue your study
of the human body, keep in mind that the proper functioning
of each organ and organ system contributes to
homeostasis. Keep in mind as well that what we call
the normal values of metabolism are often ranges, not
single numbers. Recall that normal body temperature
is a range: 97 to 99 F (36 to 38 C). Normal pulse
Organization and General Plan of the Body 11
Cells decrease
energy
production
Metabolic
rate
decreases
Bacteria
White blood cells
Hypothalamus
Heat gain
mechanisms
Key:
Stimulates Inhibits Leads to
Cells increase
heat
production
Fever
Metabolic
rate
increases
Cells increase
energy
production
Thyroid gland
Thyroxine
increases
Stimulates
thyroid
gland
Thyroxine
decreases
Thyroid gland
No longer
stimulates
thyroid gland
Metabolic
rate
increases
Hypothalamus
and pituitary gland
A
B
Hypothalamus
and pituitary gland
Figure 1–3. Feedback mechanisms. (A) The negative feedback mechanism of regulation
of metabolic rate by thyroxine. (B) The positive feedback mechanism triggered by a fever.
See text for description.
QUESTION: For each mechanism, where is the source of the “brake” or inhibition?
rate, another example, is 60 to 80 beats per minute; a
normal respiratory rate is 12 to 20 breaths per minute.
Variations within the normal range are part of normal
metabolism.
TERMINOLOGY AND GENERAL
PLAN OF THE BODY
As part of your course in anatomy and physiology,
you will learn many new words or terms. At times you
may feel that you are learning a second language, and
indeed you are. Each term has a precise meaning,
which is understood by everyone else who has learned
the language. Mastering the terminology of your profession
is essential to enable you to communicate effectively
with your coworkers and your future patients.
Although the number of new terms may seem a bit
overwhelming at first, you will find that their use soon
becomes second nature to you.
The terminology presented in this chapter will be
used throughout the text in the discussion of the organ
systems. This will help to reinforce the meanings of
these terms and will transform these new words into
knowledge.
BODY PARTS AND AREAS
Each of the terms listed in Table 1–2 and shown in
Fig. 1–4 refers to a specific part or area of the body.
For example, the term femoral always refers to the
thigh. The femoral artery is a blood vessel that passes
through the thigh, and the quadriceps femoris is a
large muscle group of the thigh.
Another example is pulmonary, which always refers
to the lungs, as in pulmonary artery, pulmonary edema,
and pulmonary embolism. Although you may not
know the exact meaning of each of these terms now,
you do know that each has something to do with the
lungs.
TERMS OF LOCATION AND POSITION
When describing relative locations, the body is always
assumed to be in anatomic position: standing upright
facing forward, arms at the sides with palms forward,
and the feet slightly apart. The terms of location are
listed in Table 1–3, with a definition and example for
each. As you read each term, find the body parts used
as examples in Figs. 1–4 and 1–5. Notice also that
these are pairs of terms and that each pair is a set of
opposites. This will help you recall the terms and their
meanings.
BODY CAVITIES AND
THEIR MEMBRANES
The body has two major cavities: the dorsal cavity
(posterior) and the ventral cavity (anterior). Each of
these cavities has further subdivisions, which are
shown in Fig. 1–5.
12 Organization and General Plan of the Body
Table 1–2 DESCRIPTIVE TERMS FOR
BODY PARTS AND AREAS
Term Definition (Refers to)
Antebrachial forearm
Antecubital front of elbow
Axillary armpit
Brachial upper arm
Buccal (oral) mouth
Cardiac heart
Cervical neck
Cranial head
Cutaneous skin
Deltoid shoulder
Femoral thigh
Frontal forehead
Gastric stomach
Gluteal buttocks
Hepatic liver
Iliac hip
Inguinal groin
Lumbar small of back
Mammary breast
Nasal nose
Occipital back of head
Orbital eye
Parietal crown of head
Patellar kneecap
Pectoral chest
Pedal foot
Perineal pelvic floor
Plantar sole of foot
Popliteal back of knee
Pulmonary lungs
Renal kidney
Sacral base of spine
Scapular shoulder blade
Sternal breastbone
Temporal side of head
Umbilical navel
Volar (palmar) palm
Dorsal Cavity
The dorsal cavity contains the central nervous system,
and consists of the cranial cavity and the vertebral or
spinal cavity. The dorsal cavity is a continuous one;
that is, no wall or boundary separates its subdivisions.
The cranial cavity is formed by the skull and contains
the brain. The spinal cavity is formed by the backbone
(spine) and contains the spinal cord. The membranes
that line these cavities and cover the brain and spinal
cord are called the meninges.
Ventral Cavity
The ventral cavity consists of two compartments, the
thoracic cavity and the abdominal cavity, which are
separated by the diaphragm. The diaphragm is a large,
dome-shaped respiratory muscle. It has openings for
the esophagus and for large blood vessels, but otherwise
is a wall between the thoracic and abdominal cavities.
The pelvic cavity may be considered a
subdivision of the abdominal cavity (there is no wall
between them) or as a separate cavity.
Organization and General Plan of the Body 13
Body Parts and Areas
Anatomic position
Cranial
Orbital
Nasal
Buccal
Axillary
Umbilical
Volar
Patellar
Plantar
Popliteal
Femoral
Inguinal
Iliac
Brachial
Mammary
Pectoral
Deltoid
Cervical
Parietal
Occipital
Lumbar
Sacral
Gluteal
Perineal
A B
Frontal
Temporal
Sternal
Antecubital
Antebrachial
Pedal
Scapular
Figure 1–4. Body parts and areas. The body is shown in anatomic position. (A) Anterior
view. (B) Posterior view. (Compare with Table 1–2.)
QUESTION: Name a body area that contains a bone with a similar name. Can you name
two more?
Cranial cavity
Foramen magnum
Spinal cavity
Dorsal
cavity
Sacral promontory
Symphysis pubis
Pelvic cavity
Abdominal cavity
Diaphragm
Thoracic cavity
Ventral
cavity
Figure 1–5. Body cavities (lateral view
from the left side).
QUESTION: Which of these cavities are
surrounded by bone?
Table 1–3 TERMS OF LOCATION AND POSITION
Term Definition Example
Superior
Inferior
Anterior
Posterior
Ventral
Dorsal
Medial
Lateral
Internal
External
Superficial
Deep
Central
Peripheral
Proximal
Distal
Parietal
Visceral
above, or higher
below, or lower
toward the front
toward the back
toward the front
toward the back
toward the midline
away from the midline
within, or interior to
outside, or exterior to
toward the surface
within, or interior to
the main part
extending from the main part
closer to the origin
farther from the origin
pertaining to the wall of a cavity
pertaining to the organs within a cavity
The heart is superior to the liver.
The liver is inferior to the lungs.
The chest is on the anterior side of the body.
The lumbar area is posterior to the umbilical area.
The mammary area is on the ventral side of the body.
The buttocks are on the dorsal side of the body.
The heart is medial to the lungs.
The shoulders are lateral to the neck.
The brain is internal to the skull.
The ribs are external to the lungs.
The skin is the most superficial organ.
The deep veins of the legs are surrounded by muscles.
The brain is part of the central nervous system.
Nerves in the arm are part of the peripheral nervous system.
The knee is proximal to the foot.
The palm is distal to the elbow.
The parietal pleura lines the chest cavity.
The visceral pleura covers the lungs.
14
Organization and General Plan of the Body 15
Organs in the thoracic cavity include the heart and
lungs. The membranes of the thoracic cavity are
serous membranes called the pleural membranes.
The parietal pleura lines the chest wall, and the visceral
pleura covers the lungs. The heart has its own set
of serous membranes called the pericardial membranes.
The parietal pericardium lines the fibrous
pericardial sac, and the visceral pericardium covers the
heart muscle.
Organs in the abdominal cavity include the liver,
stomach, and intestines. The membranes of the
abdominal cavity are also serous membranes called the
peritoneum and mesentery. The peritoneum is the
membrane that lines the entire abdominal wall, and
the mesentery is the continuation of this membrane,
folded around and covering the outer surfaces of the
abdominal organs.
The pelvic cavity is inferior to the abdominal cavity.
Although the peritoneum does not line the pelvic
cavity, it covers the free surfaces of several pelvic
organs. Within the pelvic cavity are the urinary bladder
and reproductive organs such as the uterus in
women and the prostate gland in men.
PLANES AND SECTIONS
When internal anatomy is described, the body or an
organ is often cut or sectioned in a specific way so as
to make particular structures easily visible. A plane is
an imaginary flat surface that separates two portions of
-
A
B
Figure 1–6. (A) Planes and sections of the body. (B) Cross-section and longitudinal section
of the small intestine.
QUESTION: What other organs would have sections that look like those of the small intestine?
16 Organization and General Plan of the Body
Stomach
Pancreas
Colon
Spleen
Aorta
Left kidney
Vertebra
Spinal cord
Liver
Gallbladder
Duodenum
Ribs
Inferior vena cava
Right kidney
Back Muscle
Front
C
Figure 1–6. (Continued) (C) Transverse section through the upper abdomen.
the body or an organ. These planes and sections are
shown in Fig. 1–6 (see Box 1–2: Visualizing the
Interior of the Body).
Frontal (coronal) section—a plane from side to side
separates the body into front and back portions.
Sagittal section—a plane from front to back separates
the body into right and left portions. A midsagittal
section creates equal right and left halves.
Transverse section—a horizontal plane separates the
body into upper and lower portions.
Cross-section—a plane perpendicular to the long
axis of an organ. A cross-section of the small intestine
(which is a tube) would look like a circle with
the cavity of the intestine in the center.
Longitudinal section—a plane along the long axis of
an organ. A longitudinal section of the intestine is
shown in Fig. 1–6, and a frontal section of the
femur (thigh bone) would also be a longitudinal
section (see Fig. 6–1 in Chapter 6).
AREAS OF THE ABDOMEN
The abdomen is a large area of the lower trunk of the
body. If a patient reported abdominal pain, the physician
or nurse would want to know more precisely
where the pain was. To determine this, the abdomen
may be divided into smaller regions or areas, which
are shown in Fig. 1–7.
Quadrants—a transverse plane and a midsagittal
plane that cross at the umbilicus will divide the
abdomen into four quadrants. Clinically, this is
probably the division used more frequently. The
pain of gallstones might then be described as in the
right upper quadrant.
Nine areas—two transverse planes and two sagittal
planes divide the abdomen into nine areas:
Upper areas—above the level of the rib cartilages are
the left hypochondriac, epigastric, and right
hypochondriac.
Middle areas—the left lumbar, umbilical, and right
lumbar.
Lower areas—below the level of the top of the pelvic
bone are the left iliac, hypogastric, and right
iliac.
These divisions are often used in anatomic studies
to describe the location of organs. The liver, for example,
is located in the epigastric and right hypochondriac
areas.
Organization and General Plan of the Body 17
SUMMARY
As you will see, the terminology presented in this
chapter is used throughout the text to describe the
anatomy of organs and the names of their parts. All
organs of the body contribute to homeostasis, the
healthy state of the body that is maintained by constant
and appropriate responses to internal and external
changes. In the chapters that follow, you will find
detailed descriptions of the physiology of each organ
and organ system, and how the metabolism of each is
necessary to homeostasis. We will now return to a
consideration of the structural organization of the
body and to more extensive descriptions of its levels of
organization. The first of these, the chemical level, is
the subject of the next chapter.
A B
Figure 1–7. Areas of the abdomen. (A) Four quadrants. (B) Nine regions.
QUESTION: Are there any organs found in all four abdominal quadrants?
Introduction
1. Anatomy—the study of structure.
2. Physiology—the study of function.
3. Pathophysiology—the study of disorders of functioning.
Levels of Organization
1. Chemical—inorganic and organic chemicals make
up all matter, both living and non-living.
2. Cells—the smallest living units of the body.
18 Organization and General Plan of the Body
STUDY OUTLINE
BOX 1–2 VISUALIZING THE INTERIOR OF THE BODY
A B C
Box Figure 1–A Imaging techniques. (A) CT scan of eye in lateral view showing a tumor (arrow)
below the optic nerve. (B) MRI of midsagittal section of head (compare with Figs. 8–6 and 15–1).
(C) PET scan of brain in transverse section (frontal lobes at top) showing glucose metabolism. (From
Mazziotta, JC, and Gilman, S: Clinical Brain Imaging: Principles and Applications. FA Davis,
Philadelphia, 1992, pp 27 and 298, with permission.)
In the past, the need for exploratory surgery
brought with it hospitalization, risk of infection, and
discomfort and pain for the patient. Today, however,
several technologies and the extensive use of
computers permit us to see the interior of the body
without surgery.
Computed tomography (CT) scanning uses a
narrowly focused x-ray beam that circles rapidly
around the body. A detector then measures how
much radiation passes through different tissues,
and a computer constructs an image of a thin
slice through the body. Several images may be
made at different levels—each takes only a few
seconds—to provide a more complete picture of
an organ or part of the body. The images are
much more detailed than are those produced by
conventional x-rays.
Magnetic resonance imaging (MRI) is another
diagnostic tool that is especially useful for visualizing
soft tissues, including the brain and spinal
cord. Recent refinements have produced images
of individual nerve bundles, which had not been
possible using any other technique. The patient
is placed inside a strong magnetic field, and the
tissues are pulsed with radio waves. Because
each tissue has different proportions of various
atoms, which resonate or respond differently,
each tissue emits a characteristic signal. A computer
then translates these signals into an image;
the entire procedure takes 30 to 45 minutes.
Positron emission tomography (PET) scanning
creates images that depict the rates of physiological
processes such as blood flow, oxygen
usage, or glucose metabolism. The comparative
rates are depicted by colors: Red represents the
highest rate, followed by yellow, then green, and
finally blue representing the lowest rate.
One drawback of these technologies is their cost;
they are expensive. However, the benefits to
patients are great: Highly detailed images of the
body are obtained without the risks of surgery and
with virtually no discomfort in the procedures themselves.
3. Tissues—groups of cells with similar structure and
function.
4. Organs—groups of tissues that contribute to specific
functions.
5. Organ systems—groups of organs that work
together to perform specific functions (see Table
1–1 and Fig. 1–2).
6. Person—all the organ systems functioning properly.
Metabolism and Homeostasis
1. Metabolism is the sum of all of the chemical and
physical changes that take place in the body.
Metabolic rate is the amount of energy and heat
production per unit of time.
2. Homeostasis is a state of good health maintained
by the normal metabolism (functioning) of the
organ systems.
3. The body constantly responds to internal and
external changes, yet remains stable; its many
aspects of metabolism are kept within normal limits
(usually a range of values, not a single value).
4. Negative feedback mechanism—a control system
in which a stimulus initiates a response that
reverses or reduces the stimulus, thereby stopping
the response until the stimulus occurs again and
there is a need for the response (see Fig. 1–3).
5. Positive feedback mechanism—a control system
that requires an external interruption or brake. Has
the potential to become a self-perpetuating and
harmful cycle, therefore is rare in the body (see Fig.
1–3).
Terminology and General Plan of the Body
1. Body parts and areas—see Table 1–2 and Fig. 1–4.
2. Terms of location and position—used to describe
relationships of position (see Table 1–3 and Figs.
1–4 and 1–5).
3. Body cavities and their membranes (see Fig. 1–5).
• Dorsal cavity—lined with membranes called
meninges; consists of the cranial and vertebral
cavities.
Cranial cavity contains the brain.
Vertebral cavity contains the spinal cord.
• Ventral cavity—the diaphragm separates the thoracic
and abdominal cavities; the pelvic cavity is
inferior to the abdominal cavity.
Thoracic cavity—contains the lungs and heart.
— Pleural membranes line the chest wall and
cover the lungs.
— Pericardial membranes surround the
heart.
Abdominal cavity—contains many organs
including the stomach, liver, and intestines.
— The peritoneum lines the abdominal cavity;
the mesentery covers the abdominal
organs.
Pelvic cavity—contains the urinary bladder
and reproductive organs.
4. Planes and sections—cutting the body or an organ
in a specific way (see Fig. 1–6).
• Frontal or coronal—separates front and back
parts.
• Sagittal—separates right and left parts.
• Transverse—separates upper and lower parts.
• Cross—a section perpendicular to the long axis.
• Longitudinal—a section along the long axis.
5. Areas of the abdomen—permits easier description
of locations:
• Quadrants—see Fig. 1–7.
• Nine areas—see Fig. 1–7.
Organization and General Plan of the Body 19
REVIEW QUESTIONS
1. Explain how the physiology of a bone is related to
its anatomy. Explain how the physiology of the
hand is related to its anatomy. (p. 4)
2. Describe anatomic position. Why is this knowledge
important? (p. 12)
3. Name the organ system with each of the following
functions: (p. 7)
a. Moves the skeleton
b. Regulates body functions by means of hormones
c. Covers the body and prevents entry of
pathogens
d. Destroys pathogens that enter the body
e. Exchanges oxygen and carbon dioxide between
the air and blood
1. The human foot is similar to the human hand, but
does have anatomic differences. Describe two of
these differences, and explain how they are related
to the physiology of the hand and the foot.
2. Complete each statement using the everyday term
for the body part.
a. The distal femoral area is immediately superior
to the ____.
b. The proximal brachial area is immediately inferior
to the ____.
c. The patellar area is directly proximal to the
____.
d. The volar area is directly distal to the ____.
3. Name a structure or organ that is both superior and
inferior to the brain. Name one that is both anterior
and posterior.
4. If a person has appendicitis (inflammation of the
appendix caused by bacteria), pain is felt in which
abdominal quadrant? (If you’re not sure, take a
look at Fig. 16–1 in Chapter 16.) Surgery is usually
necessary to remove an inflamed appendix before it
ruptures and causes peritonitis. Using your knowledge
of the location of the peritoneum, explain why
peritonitis is a very serious condition.
5. Keep in mind your answer to Question 4, and
explain why bacterial meningitis can be a very serious
infection.
6. Use a mental picture to cut the following sections.
Then describe in simple words what each section
looks like, and give each a proper anatomic name.
First: a tree trunk cut top to bottom, then cut side
to side.
Second: a grapefruit cut top to bottom (straight
down from where the stem was attached), then
sliced through its equator.
20 Organization and General Plan of the Body
FOR FURTHER THOUGHT
4. Name the two major body cavities and their subdivisions.
Name the cavity lined by the peritoneum,
meninges, and parietal pleura. (pp. 13, 15)
5. Name the four quadrants of the abdomen. Name at
least one organ in each quadrant. (p. 17)
6. Name the section through the body that would
result in each of the following: equal right and left
halves, anterior and posterior parts, superior and
inferior parts. (pp. 15–16)
7. Review Table 1–2, and try to find each external area
on your own body. (pp. 12–13)
8. Define cell. When similar cells work together, what
name are they given? (p. 4)
9. Define organ. When a group of organs works
together, what name is it given? (p. 6)
10. Define metabolism, metabolic rate, and homeostasis.
(pp. 7, 10)
a. Give an example of an external change and
explain how the body responds to maintain
homeostasis
b. Give an example of an internal change and
explain how the body responds to maintain
homeostasis
c. Briefly explain how a negative feedback mechanism
works, and how a positive feedback
mechanism differs