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