Body Planes and Cavities Quiz

A Closer Look

Medical Imaging: Illuminating the Body

Y bombarding the body with en-

ergy, new scanning techniques

can reveal the structure of inter-

nal organs, and wring out informa-

tion about the private and, until

now, secret working of their mole-

cules. These new imaging tech-

niques are changing the face of

medical diagnosis.

Until about 50 years ago, the

magical but murky X ray was the only

means of peering into a living body.

What X rays did and still do best was

visualize hard, bony structures and

locate abnormally dense structures

(tumors, tuberculosis nodules) in the

lungs. The 1950s saw the birth of nu-

clear medicine, which uses radioiso-

topes to scan the body, and ultra-

sound techniques. In the 1970s, CT,

PET, and MRI scanning techniques

were introduced.

The best known of new imaging

devices is computed tomography

(CT) (formerly called computerized

axial tomography [CAT]), a refined

version of X ray. A CT scanner con-

fines its beam to a thin slice of the

body and ends the confusion result-

ing from images of overlapping struc-

tures seen in conventional X rays.

CT's clarity has all but eliminated

exploratory surgery. As the patient is

slowly moved through the doughnut-

shaped CT machine, its X-ray tube

rotates around the body. Different tis-

sues absorb the radiation in varying

amounts. The device's computer

20

translates this information into a de-

tailed, cross-sectional picture of the

body region scanned. CT scans are at

the forefront in evaluating most prob-

lems that affect the brain (see photo

a), abdomen, and calcification of the

coronary arteries in those at an ele-

vated risk for heart disease. Special

ultrafast CT scanners have produced

a technique called dynamic spatial re-

construction (DSR), which provides

three-dimensional images of body or-

gans from any angle. It also allows

their movements and changes in

their internal volumes to be observed

at normal speed, in slow motion, and

at a specific moment in time. Al-

though DSR can be used to evaluate

the lungs and certain other mobile or-

gans, its greatest value has been to

visualize the heart beating and blood

flowing through blood vessels. This

allows heart defects, constricted

blood vessels, and the status of coro-

nary bypass grafts to be assessed.

Another computer-assisted X-ray

technique is digital subtraction an-

giography (DSA) (angiography

vessel pictures). This technique

provides an unobstructed view of dis-

eased blood vessels. Conventional

radiographs are taken before and af-

ter a contrast medium is injected into

an artery. Then the computer sub-

tracts the "before" image from the

'after" image, eliminating all traces

of body structures that obscure the

vessel. DSA is often used to identify

blockages in the arteries that supply

the heart wall and the brain (photo b).

Just as the X ray spawned "new

technologies, " so did nuclear medi-

cine in the form of positron emis-

Sion tomography (PET). PET excels

in observing metabolic processes.

PET's greatest clinical value has

been its ability to provide insights

into brain activity in those affected

by mental illness, Alzheimer's dis-

ease, and epilepsy. One of its most

exciting uses is to determine which

areas of the healthy brain are most

active during certain tasks (speak-

ing, listening to music, and so on).

The patient is given an injection of

short-lived radioisotopes that have

been tagged to biological molecules

(such as glucose) and then posi-

tioned in the PET •scanner. As the

radioisotopes are absorbed by the

most active brain cells, high-energy

gamma rays are produced. The com-

puter analyzes the gamma emission

and produces a picture of the brain's

biochemical activity in vivid colors.

Ultrasound imaging, or ultra-

sonography, has distinct advantages

over the approaches described so

far: the equipment is inexpensive

and it employs high-frequency sound

waves (ultrasound) as its energy

source. Ultrasound, unlike ionizing

forms of radiation, has no harmful ef-

fects on living tissues (as far as we

know). The body is probed with

pulses of sound waves, which cause

echos when reflected and scattered

oy body tissues. The echoes are ana-

yzed by computer to construct visual

images of body organs of interest.

Because of its safety, ultrasound is

the imaging technique of choice for

obstetrics, that is, for determining

•etal age and position and locating

Zhe placenta. Because sound waves

nave very low penetrating power and

ere rapidly scattered in air, ultra-

sonography is of little value for look-

ng at air-filled structures (the lungs)

or those surrounded by bone (the

orain and spinal cord).

Another technique that depends

on nonionizing radiation is magnetic

resonance imaging (MR/), which

uses magnetic fields up to 60,000

tmes stronger than the Earth's to

cry information from the body's tis-

sues. The patient lies in a chamber

Nithin a huge magnet. Hydrogen

molecules spin like tops in the mag-

•etic field, and their energy is en-

tanced by radio waves. When the

-adio waves are turned off, the en-

ergy is released and translated by

the computer into a visual image.

MRI is immensely popular because

et can do many things a CT scan

cannot. Dense structures do not

show up in MRI, so bones of the

skull and/or vertebral column do not

Impair the view of soft tissues such

as the brain (see Figure 1.6a, p. 16).

MRI is also particularly good at de-

-.ecting degenerative disease of vari-

ous kinds. Multiple sclerosis plaques,

•or example, do not show up well in

CT scans but are dazzlingly clear in

Artery supplying

heart

(a)

Narrowing

of the artery

(b)

Two different methods for illuminating the body. (a) CT scan

showing a brain tumor (oval area on right side of brain). (b) DSA image of

arteries supplying the heart.

MRI scans. A key issue being investi-

gated by MRI studies is how brain

development and behavior change

with growth or experience.

A newer variation of MRI, called

magnetic resonance spectroscopy

(MAS), maps the distribution of ele-

ments other than hydrogen to reveal

more about how disease changes

body chemistry. In 1992, MRI tech-

nology leaped forward with the

development of the functional MRI,

which allows tracking of blood flow

into the brain in real time. Until then,

matching thoughts, deeds, and dis-

ease to corresponding brain activity

had been the sole domain of PET.

Because functional MRI does not re-

quire injections of tracer elements, it

provides another, perhaps more de-

sirable, alternative to such studies.

Despite its advantages, the powerful

magnets of the MRI present some

problems. For example they can

'suck" metal objects, such as im-

planted pacemakers and loose tooth

fillings, through the body. Also, there

is no convincing evidence that such

magnetic fields are risk free.

As you can see, modern medical

science has many remarkable tools

at its disposal. CT and PET scans ac-

count for about 25 percent of all im-

aging. Ultrasonography, because of

its safety and low cost, is the most

widespread of the new techniques.

Conventional X rays remain the work-

horse of diagnostic imaging tech-

niques and still account for more than

half of all imaging currently done.

21

22 Essentials of Human Anatomy and Physiology

SUMMARY

Media study tools that could provide you with addi-

tional help in reviewing specific key topics of Chapter 1

are referenced below.

Interactive Physiology;

= Place website.

AN OVERVIEW OF ANATOMY AND

PHYSIOLOGY

1. Anatomy is the study of structure. Observation is

used to see the sizes and relationships of body

parts.

2. Physiology is the study of how a structure (which

may be a cell, an organ, or an organ system) func-

tions or works.

3. Structure determines what functions can occur;

therefore, if the structure changes, the function

must also change.

LEVELS OF STRUCTURAL ORGANIZATION

(pp. 2-7)

1. There are six levels of structural organization.

Atoms (at the chemical level) combine, forming the

unit of life, the cell. Cells are grouped into tissues,

which in turn are arranged in specific ways to form

organs. A number of organs form an organ system

that performs a specific function for the body

(which no other organ system can do). Together, all

of the organ systems form the organism, or living

body.

Exercise: Chapter 1, Levels of Biological

Organization.

2. For a description of organ systems naming the ma-

jor organs and functions, see pp. 3—7.

MAINTAINING LIFE (pp. 7-9)

1. To sustain life, an organism must be able to main-

tain its boundaries, move, respond to stimuli, digest

ie and excrete wastes, carry on metabolism,

reproduce itself, an grow.

2. Survival needs include food, oxygen, water, appropri-

ate temperature, and normal atmospheric pressure.

Extremes of any of these factors can be harmful.

HOMEOSTASIS (pp. 9-11)

1. Body functions interact to maintain homeostasis, or

a relatively stable internal environment within the

body. Homeostasis is necessary for survival and

good health; its loss results in illness or disease.

All homeostatic control mechanisms have a receptor

that responds to environmental changes and a con-

trol center that assesses those changes and produces

a response by activating a third element, the effector.

Most homeostatic control systems are negative feed-

back systems, which act to reduce or stop the initial

stimulus.

THE LANGUAGE OF ANATOMY

(pp. 11-19)

Anatomical terminology is relative and assumes that

the body is in the anatomical position (erect, palms

facing forward).

Regional terms. Visible landmarks on the body sur-

face may be used to specifically refer to a body part

or area. See pp. 12 and 13 for terms referring to an-

terior and posterior surface anatomy.

Exercise: Chapter 1, Anatomical Terminology:

Orientation and Directional Terms.

Directional terms

a.

b.

c.

d.

e.

f.

g.

h.

i.

j.

k.

Superior (cranial, cephalad): above something

else, toward the head.

Inferior (caudal): below something else, toward

the tail.

Anterior (ventral): toward the front of the body

or structure.

Posterior (dorsal): toward the rear or back of

the body or structure.

Medial: toward the midline of the body.

Lateral: away from the midline of the body.

Intermediate: between a more medial and a

more lateral structure.

Proximal: closer to the point of attachment.

Distal: farther from the point of attachment.

Superficial (external): at or close to the body

surface.

Deep (internal): below or away from the body

surface.

Body planes and sections

a. Sagittal section: separates the body longitudi-

nally into right and left parts.

Chapter 1: The Human Body: An Orientation 23

b.

c.

Frontal (coronal) section: separates the body on

a longitudinal plane into anterior and posterior

parts.

Transverse (cross) section: separates the body on

a horizontal plane into superior and inferior parts.

WEB Exercise: Chapter 1, Body Planes.

5. Body cavities

Anatomical terms that apply to the backside of the

body in the anatomical position include

a. ventral and anterior.

b. back and rear.

c. posterior and dorsal.

d. head and lateral.

A neurosurgeon orders a spinal tap for a patient.

a. Into what body cavity will the needle be inserted?

b.

Dorsal: well protected by bone; has two subdi-

visions.

(1) Cranial: contains the brain.

(2) Spinal: contains the spinal cord.

Ventral: less protected than dorsal cavity; has

two subdivisions.

(1) Thoracic: The superior cavity that extends

inferiorly to the diaphragm; contains heart

and lungs, which are protected by the rib

cage.

(2) Abdominopelvic: The cavity inferior to the

diaphragm that contains the digestive, uri-

nary, and reproductive organs. The abdom-

inal portion is vulnerable because it is

protected only by the trunk muscles. There

is some protection of the pelvic portion by

the bony pelvis. The abdominopelvic cavity

is often divided into four quadrants or nine

regions (see Figure 1.8).

a. Ventral

b. Thoracic

c. Dorsal

d. Cranial

e. Pelvic

Which of the following groupings of the ab-

dominopelvic regions is medial?

a.

b.

c.

d.

e.

Hypochondriac, hypogastric, umbilical

Hypochondriac, lumbar, inguinal

Hypogastric, umbilical, epigastric

Lumbar, umbilical, iliac

Iliac, umbilical, hypochondriac

SHORT ANSWER ESSAY

WEB Exercise: Chapter 1, Dorsal and Ventral Cavities.

REVIEW QUESTIONS

MULTIPLE CHOICE

-Ilore than one choice may apply.

1. Consider the following levels: (1) chemical; (2) tis-

sue; (3) organ; (4) cellular; (5) organismal; (6) sys-

temic. Which of the following choices has the levels

listed in order of increasing complexity?

a.

b. 1, 4, 2, 5, 3,6 e.

2. Which of the following

taining homeostasis?

is (are) involved in main-

Feedback

Lack of change

Define anatomy and physiology.

Why would you have a hard time trying to learn

and understand physiology if you did not also un-

derstand anatomy?

List the 11 organ systems of the body, briefly de

scribe the function of each, and then name two or-

gans in each system.

In addition to being able to metabolize, grow, di-

gest food, and excrete wastes, what functions must

an organism perform if it is to survive?

Define homeostasis.

What is the consequence of loss of homeostasis, or

homeostatic imbalance?

Describe the anatomical position.

On what body surface is each of the following 10

cated: nose, calf of leg, ears, umbilicus, fingernails?

Several pairs of structures are given next. In each case,

choose the one that meets the condition given first.

a. Effector d.

b. Control center e.

c. Receptor

3. Which is not essential to survival?

a.

b.

c.

d.

e.

Distal—the knee/the foot

Lateral—the cheekbone/the nose

Superior—the neck/the chin

Anterior—the heel/the toenails

a. External—the skin/the skeletal muscles

b.

c.

Water

Oxygen

Gravity

d. Atmospheric pressure

e. Nutrients What kind of section would have to be made to cut

the brain into anterior and posterior parts?