CHAPTER 22
Respiration: The Exchange of Gases
MECHANISMS OF GAS EXCHANGE
• Gas exchange is the interchange of O2 and CO2
between an organism and its environment
– It is also called respiration
Overview: Gas exchange involves breathing,
the transport of gases, and the servicing of
tissue cells
• Gas exchange is essential because energy
metabolism requires O2 and produces CO2
food
O2
ATP
CO2
Animals exchange O2 and CO2 through
moist body surfaces
• O2 enters an animal and CO2 leaves by
diffusion through a respiratory surface
– Respiratory surfaces are made up of living cells
Lungs




trachea
bronchi
bronchioles
alveoli
capillaries
(circulatory system)
alveoli
The human respiratory system
• In humans and other
mammals, air enters
through the nasal
cavity
– It passes through the
pharynx and larynx into
the trachea
– The trachea forks to
form two bronchi
– Each bronchus branches
into numerous
bronchioles
The human respiratory system
• The bronchioles end in
clusters of tiny sacs
called alveoli
• Alveoli form the
respiratory surface of the
lungs
– Oxygen diffuses
through the thin
walls of the
alveoli into
the blood
Connection: Smoking is one of the deadliest
assaults on our respiratory system
• Mucus and cilia in the
respiratory passages
protect the lungs
– Pollutants, including
tobacco smoke, can
destroy these protections
• Smoking kills about
430,000 Americans each
year
Connection: Smoking is one of the deadliest
assaults on our respiratory system
• Smoking causes lung cancer
and contributes to heart
disease
• Smoking also causes
emphysema
– Cigarette smoke
makes alveoli
brittle, causing
them to rupture
– This reduces the
lungs’ capacity
for gas exchange
Breathing ventilates the lungs
• Breathing is the alternation of inhalation (active) and
exhalation (passive)
Negative pressure breathing
• Diaphragm moves down & expands chest cavity
pulls air into lungs
inhale
exhale
Automatic Brain Control
• You don’t have to think to breathe!
– medulla & pons
– measure blood pH
• CO2 = pH (acid)
– coordinate
breathing,
heart rate &
body’s need
for energy
– Medulla oblongata
will stimulate
diaphragm to contract.
TRANSPORT OF GASES IN THE BODY
• Blood transports the respiratory gases, with
hemoglobin carrying the oxygen
• The heart pumps oxygen-poor blood to the lungs
– In the lungs it picks up O2 and drops off CO2(external
respiration)
– In the tissues, cells pick up CO2 and drop off O2-(Internal
respiration)
– Gases diffuse down pressure gradients in the lungs
and the tissues
Gas exchange: Diffusion of gases
• Gases move by diffusion from high to low
concentration
– capillaries are thin-walled tubes of circulatory
system
– alveoli are thin-walled sacs of respiratory system
capillaries in lungs
capillaries in muscle
O2
O2
O2
O2
CO2
CO2
CO2
CO2
blood
lungs
blood
body
Gas exchange in the body
Hemoglobin is a protein in red blood cells
– It carries most of the oxygen in the blood
Heme
group
Iron
atom
O2 loaded
in lungs
O2 unloaded
in tissues
Polypeptide chain
O2
O2
Hemoglobin helps transport CO2 and
buffer the blood
• Hemoglobin helps buffer the
pH of blood and carries some
CO2
• Most CO2 in the blood
combines with water to form
carbonic acid
– The carbonic acid breaks down
to form H+ ions and
bicarbonate ions
– These help buffer the blood
Transport of CO2
• Most CO2 is transported
to the lungs in the form
of bicarbonate ions
Connection: The human fetus exchanges
gases with the mother’s bloodstream
• A human fetus depends on
the placenta for gas exchange
• A network of capillaries
exchanges O2 and CO2 with
maternal blood that carries
gases to and from the
mother’s lungs
• At birth, increasing CO2 in the
fetal blood stimulates the
fetus’s breathing control
centers to initiate breathing
Placenta, containing
maternal blood vessels
and fetal capillaries
Umbilical cord,
containing fetal
blood vessels
Amniotic
fluid
Uterus
Breathing and Homeostasis
• Homeostasis
ATP
– keeping the internal environment of the
body balanced
– need to balance O2 in and CO2 out
– need to balance energy (ATP) production
• Exercise
– breathe faster
O2
• need more ATP
• bring in more O2 & remove more CO2
• Disease
– poor lung or heart function = breathe faster
• need to work harder to bring in O2 & remove CO2
CO
Disorders of the Respiratory system
• Asthma: a severe allergic reaction in which contraction of the
bronchioles makes breathing difficult
• Bronchitis: an inflammation of the lining of the bronchial
tubes. The passageways to the alveoli become swollen and
clogged with mucus
• Emphysema: lungs lose their elasticity, deterioration of the
lung structure
• Pneumonia: alveoli become filled with fluid. Caused by
bacterial or viral infection
• Lung Cancer: a disease in which tumors form in the lungs as a
result of irregular and uncontrolled cell growth