6.4 Gas exchange
http://www.siumed.edu/surgery/cardiothor
http://www.emphysemafoundation.org/in
6.4
• Essential idea: The lungs are actively ventilated
to ensure that gas exchange can occur passively.
• Cellular respiration is the controlled release of
energy in the form of ATP from organic
compounds in cells. It is a continuous process in
all cells.
Aerobic:
C6H12O6 + 6O2  6CO2 + 6H2O + ATP
• To support aerobic cellular respiration, cells take
in oxygen from their environment and give out
carbon dioxide, by a process called gas exchange.
• Gas exchange ultimately relies on diffusion.
•
All animal respiratory systems share two
features that facilitate diffusion:
1. Respiratory system must remain moist (gases
must be dissolved in water to diffuse into or out
of cells)
2. Respiratory system must have large surface area
in contact with environment to allow adequate
gas exchange
•
Most animals have evolved specialized
respiratory systems
6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide
between air in alveoli and blood flowing in adjacent capillaries.
• In general, gas exchange in most respiratory
systems occurs in the following stages:
1. Air or water, containing oxygen, is moved past a
respiratory system by bulk flow (fluids or gases
move in bulk through relatively large spaces,
from areas of higher pressure to areas of lower
pressure) – commonly facilitated by muscular
breathing movements
6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide
between air in alveoli and blood flowing in adjacent capillaries.
O2
2. Oxygen and carbon
dioxide are exchanged
through the respiratory
surface by diffusion;
oxygen is carried into
capillaries of circulatory
system and carbon
dioxide is removed
CO2
Capillary
6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide
between air in alveoli and blood flowing in adjacent capillaries.
3. Gases are
transported between
respiratory system
and tissues by bulk
flow of blood as it is
pumped throughout
body by heart
6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide
between air in alveoli and blood flowing in adjacent capillaries.
4. Gases are exchanged between tissues and
circulatory system by diffusion (oxygen diffuses
out into tissue and carbon dioxide diffuses into
capillaries based on concentration gradients)
6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide
between air in alveoli and blood flowing in adjacent capillaries.
• Because the lungs are protected in the thorax
(chest), air must be brought in.
• This results in the need for a ventilation system:
▫ A ventilation system is a pumping mechanism
that moves air into and out of the lungs efficiently,
thereby maintaining the concentration gradient
for diffusion.
6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide
between air in alveoli and blood flowing in adjacent capillaries.
• Human Respiratory System (and other
vertebrates) is divided into two parts:
▫ The conducting portion – series of passageways
that carry air to gas-exchange portion
▫ The gas exchange portion – gas is exchanged with
the blood in tiny sacs in lungs
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli
in bronchioles.
Passageway of air in respiratory system:
• Nostrils – air enters body
• Nasal cavities – air is warmed, filtered and
moistened
▫ Lined with ciliated epithelium that trap particles
in mucus and move it to the throat to be
swallowed
Cilia
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli
in bronchioles.
#3
#1 Nose
#2 Mouth
• Pharynx – back of
nasal cavities that is
continuous with the
throat; passageway
for both food and air
Pharynx
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli
in bronchioles.
• Epiglottis – flap of
tissue that
automatically covers
opening to larynx
during swallowing;
prevents food from
entering lungs
• Larynx – Pharynx
leads to Larynx “voice
box”
▫ Contains vocal cords
▫ Cartilage is embedded
in walls to prevent
collapse
Epiglottis
#5
Larynx
#4
Epiglottis
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli
in bronchioles.
• Trachea – also called
windpipe; tube that
carries air down to
lungs – reinforced
with cartilage to
prevent collapse
• Bronchi – two
branches off the
trachea that lead to a
lung
#6
Trachea
Lungs
#7
Bronchus
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli
in bronchioles.
• Bronchioles – smaller tubes
of the bronchi that lead to
the alveoli
Bronchiole
Bronchioles
#8
#9
Alveoli
• Lungs – large, paired spongy organs
▫ Right lung is divided into 3 lobes
▫ Left lung is divided into 2 lobes
▫ Each is covered by a pleural membrane – forms a
sac and lines the thoracic cavity
▫ Secretes a fluid that provides lubrication between
lungs and chest wall
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli
in bronchioles.
• Alveoli – each bronchiole ends
in a cluster of tiny air sacs
▫ Numerous small clusters for
increased surface area
▫ Walls of alveoli are extremely
thin (one cell thick)
6.4.U2 Type I pneumocytes are extremely thin alveolar cells that are adapted to carry
out gas exchange. AND 6.4.U3 Type II pneumocytes secrete a solution containing
surfactant that creates a moist surface inside the alveoli to prevent the sides of the
alveolus adhering to each other by reducing surface tension.
▫ Two types of cells make up the
alveoli wall:
 Type I pneumocytes – extremely
thin; adapted to carry out gas
exchange
 Type II pneumocytes – secrete a
solution containing surfactant
that allow gases to dissolve and
diffuse, prevents walls of alveoli
from sticking together &
decreases surface tension
making it easier to inflate
http://www.ubccriticalcaremedicine.ca/rotating/
6.4.U1 Students should be able to draw a diagram
to show the structure of an alveolus and an
adjacent capillary
Type I pneumocytes in
alveolus wall
Phagocyte
Network of blood capillaries
Type II pneumocytes in alveolus wall
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli
in bronchioles.
▫ Alveoli are surrounded by
capillaries
▫ Gases diffuse freely through the
wall of the alveolus and capillary
(oxygen diffuses into blood and
CO2 diffuses into alveoli)
CO2
Capillary
6.4.U5 Muscle contractions cause the pressure changes inside the thorax that force
air in and out of the lungs to ventilate them.
• Breathing (ventilation) is the mechanical process
of moving air from the environment into the
lungs and expelling air from the lungs
▫ The thorax is an airtight chamber and pressure
changes in the lungs occurs when the volume of
the thorax changes
▫ Pressure changes allow for air to be forced into or
out of the lungs
6.4.U6 Different muscles are required for inspiration and expiration because
muscles only do work when they contract.
▫ Inspiration (inhalation):
 Diaphragm (dome-shaped muscle
forming floor of thoracic cavity)
contracts and moves downward
 Abdominal muscles relax
 External intercostal rib muscles
contract lifting ribs up and out
(internal intercostal muscles relax)
 This increases volume of thoracic
cavity which lowers air pressure
inside (below atmospheric pressure)
 Air from outside rushes into lungs to
equalize air pressure
6.4.U6 Different muscles are required for inspiration and expiration because
muscles only do work when they contract.
▫ Expiration (exhalation)
 Diaphragm relaxes and returns to
dome-shape (moves up)
 Internal intercostal muscles contract
causing ribs to drop back down
(external intercostal muscles relax)
 This decreases the volume of the
thoracic cavity which increases air
pressure inside
 Air from inside lungs rushes out to
equalize air pressure
 When you breathe forcefully, your
abdominal muscles also contract. This
squeezes your abdominal organs
which puts pressure on the
diaphragm.
6.4.A3 External and internal intercostal muscles, and diaphragm and abdominal
muscles as examples of antagonistic muscle action.
Expiration
Inspiration
Diaphragm contracts
(moves down)
Abdominal muscles relax
External intercostal muscles contract
Internal intercostal muscles relax
Diaphragm relaxes
(moves up)
Abdominal muscles contract
External intercostal muscles relax
Internal intercostal muscles contract
•
Control of Breathing Rate
▫
▫
▫
Breathing rate is controlled by the respiratory
center in brain – located in medulla just above
spinal cord
muscles are stimulated to contract by impulses
from respiratory center
nerve cells in respiratory center generate cyclic
bursts of impulses that cause the alternating
contraction and relaxation of respiratory muscles
▫
▫
▫
Respiratory center receives input from several
sources and adjusts breathing rate and volume
to meet body’s changing needs
CO2 concentration in blood is the most
important chemical stimulus for regulating rate
of respiration
Chemoreceptors in medulla, and in walls of the
aorta and carotid arteries are sensitive to
changes in arterial CO2 concentration
6.4.A2 Causes and consequences of emphysema.
Emphysema is a chronic lung
disease. The large number of
small alveoli are replaced by a
small number of much larger
much less elastic air spaces.
http://www.humanillnesses.c
om/original/images/hdc_00
6.4.A2 Causes and consequences of emphysema.
Consequences:
Total surface area for gas exchange is considerably reduced & the
distance over which diffusion of gases occurs is increased, so gas
exchange is much less effective. Lungs become less elastic, so
ventilation is more difficult.
Symptoms are
breathlessness and forced
breathing. It is a type of
chronic obstructive
pulmonary disease (COPD).
It is a progressive disease
for which there is no cure.
http://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/articles/h
6.4.A2 Causes and consequences of emphysema.
Causes:
• Cigarette smoking
Leading causes
• Air pollution
• Marijuana smoking
• Manufacturing fumes
• Alpha-1-antitrypsin deficiency
emphysema (rare)
Eric Lawson, known as
the Marlboro man, died
of respiratory failure as a
result of COPD. He
began smoking at age 14.
http://www.huffingtonpost.
com/2014/01/27/ericlawson-marlboro-mandies_n_4671746.html
6.4.A2 Causes and consequences of emphysema.
How do the alveoli become damaged?
1. Cilia become damaged and cease
to function and mucus builds up,
causing infection.
2. Toxins in cigarette smoke and
polluted air cause inflammation
and damage to white blood cells
in the lungs.
3. Protease (trypsin) is released
from damaged cells &
phagocytes which digest elastic
fibers in the lungs and eventually
causes complete breakdown of
alveolus walls.
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6.4.A1 Causes and consequences of lung cancer.
Lung cancer is the most common cancer in the world, both
in terms of the number of cases and deaths.
http://www.lungevity.org/aboutlung-cancer/lung-cancer101/screening-early-detection
6.4.A1 Causes and consequences of lung cancer.
Causes:
• Cigarette smoking – tobacco smoke
contains many carcinogens; causes
nearly 90% of all cases
• Second hand smoke (passive
smoking)
• Air pollution
• Radon gas – in some areas it leaks
out of rocks, especially granite
• Asbestos and silica
Healthy lung
Lung with tar
deposits
http://www.bbc.co.uk/education/guides/zpn9q6f/revisio
http://www.who.int/tobacco/healthwarningsdatabase/toba
6.4.A1 Causes and consequences of lung cancer.
Consequences:
• Difficulties breathing
• Persistent coughing
• Coughing up blood
• General fatigue
• Chest pain
• Loss of appetite
• Weight loss
Only 15% of patients with lung
cancer survive for more than 5
years. If caught early enough, all
or part of the affected lung may
be removed. Chemotherapy and
radiation may also be needed.
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