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CHAPTER 22Respiration: 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
CO2
O2 ATP
food
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
alveoli
trachea bronchi bronchioles alveoli
capillaries(circulatory system)
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 thelungs’ 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
blood lungs
CO2
O2
CO2
O2
blood body
CO2
O2
CO2
O2
capillaries in lungs capillaries in muscle
Gas exchange in the body
Hemoglobin is a protein in red blood cells
– It carries most of the oxygen in the blood
Hemegroup Iron
atom
O2 loadedin lungs
O2 unloadedin 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, containingmaternal blood vesselsand fetal capillaries
Umbilical cord,containing fetalblood vessels
Uterus
Amnioticfluid
Breathing and Homeostasis• Homeostasis– 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
• 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
O2
ATP
CO2
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