HUMAN BIOLOGY

ExpLorEon yoUr oWn

sUmmary

section 10.1 The respiratory system

brings air, which contains oxygen, into the

body and disposes of carbon dioxide by way

of exhaled air.

Airways include the nasal cavity, pharynx,

larynx, trachea, bronchi, and bronchioles. Gas

exchange occurs in millions of saclike alveoli

located at the end of the terminal respiratory bronchioles.

Airways lead to the lungs, which are elastic organs located

in the rib cage above the diaphragm. They are separated by

the heart.

section 10.2 Respiration brings oxy-

gen from air into the blood and removes carbon

dioxide from blood. Both these processes

occur in the lungs. The cardiovascular system

partners with the respiratory system as it

circulates blood throughout the body.

Air is a mixture of oxygen, carbon dioxide, and other

gases. Each gas exerts a partial pressure, and each tends

to move (diffuse) from areas of higher to lower partial

pressure. Following pressure gradients, oxygen diffuses into

deoxygenated blood in the lungs, and carbon dioxide diffuses

from the blood into the lungs to be exhaled.

In respiration, oxygen and carbon dioxide diffuse across a

respiratory surface—a moist, thin layer of epithelium in the

alveoli of the lungs. Airways carry gases to and from one side

of the respiratory surface, and blood vessels carry gases to and

away from the other side.

section 10.4 Breathing ventilates the

lungs in a respiratory cycle. During inspira-

tion (inhalation), the chest cavity expands,

pressure in the lungs falls below atmospheric

pressure, and air flows into the lungs. During

normal expiration (exhalation), these steps

are reversed.

The volume of air in a normal breath, called the tidal

volume, is about 500 milliliters. Vital capacity is the maximum

volume of air that can move out of the lungs after you inhale

as deeply as possible.

section 10.5 Driven by its partial

pressure gradient, oxygen in the lungs

diffuses from alveoli into pulmonary

capillaries. Then it diffuses into red blood

cells and binds with hemoglobin, forming

oxyhemoglobin. In tissues where cells are

metabolically active, hemoglobin gives up

oxygen, which diffuses out of the capillaries, across tissue

fluid, and into cells.

air pollution is a serious problem in many parts of the world.

Even if you don’t live near a large urban area, you may be breathing the

kinds of air pollutants shown in the chart in Figure 10.23. The ultrafine par-

ticulates can stay in the air for weeks or months before they settle to Earth

or are washed down by rain, and all of them are known to cause respira-

tory problems, especially in people who have asthma or emphysema.

Explore this health issue by finding out if your community monitors its

air quality. If so, what do authorities consider to be the greatest threats

to the health of you and your fellow citizens? Where do these pollutants

come from?

Figure 10.23 Particles from numerous sources may be present in the air you breathe.

Ultrafine particles Fine particles Large particles

sea salt

carbon black

cement dust

metallurgical dust, fumes

photochemical smog

paint pigments

combustion

oil smoke

tobacco smoke

fly ash

coal dust

milled flour

pollen

insecticide dust

Don Hopey/

Pittsburgh Post-Gazette

, 2002, all rights reserved. Reprinted with permission

192 ChapteR 10

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