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Bio 20 C7.2 & 7.3 Breathing, Respiration, Disorders
Two Muscles and Changes in Air Pressure are Responsible for the Mechanics of
Breathing
p. 249
 Check out this clip https://www.youtube.com/watch?v=lr5dDmTASos
The first half shows how air pressure changes during breathing.
• Two muscles, the diaphragm and the intercostals (rib muscles), work simultaneously to
move air in and out of the lungs, by controlling the air pressure inside the lungs.
• The diaphragm is a dome-shaped layer of muscle that separates the lung region (the
thoracic cavity) from the abdominal cavity.
• The intercostals (rib muscles) are between the ribs and along the ventral (front) inside
surface of the ribs.
• The air in your lungs
moves passively from
areas of high pressure
to low pressure during
inhalation and
exhalation.
Inhalation results from muscle contraction
 intercostals and diaphragm contract
 the rib cage moves up and out and floor of chest cavity (the diaphragm) moves downward
 volume of thoracic cavity increases (the thoracic cavity is air tight)
 air pressure in thoracic cavity decreases so air pressure in the lungs decreases 
(because the air in the lungs now fills a larger space)
 air moves into the lungs because pressure in lungs is less than in the environment
(remember air moves from high pressure to low pressure).
Exhalation results from muscle relaxation (just the reverse of inhalation)
 diaphragm and intercostals relax, decreasing the volume of thoracic cavity
 this decreases the lung volume so air pressure in the lungs increases 
 air moves from high pressure in the lungs to the lower pressure of air in the
environment outside of the body
NB: the air pressure in the environment is NOT changing, just in the lungs and thoracic
cavity.
Learning check!
1. What are the 2 main muscles used for breathing? Where are they located?
2. Put HIGH and LOW Pressure on figures above.
 Check out Figure 7.5 pg. 249: Inhalation and Exhalation
 Make lung model (See #3, pg. 254). Go through the inhalation and exhalation steps
listed above with your model.

Use the information below to answer the following questions
Fig. 1. Pressure in the Thoracic Cavity during a Normal Breath.
Y axis is atmospheric pressure (kPa). X axis is time in seconds (A-E is 3 seconds). 101.3 KPa
is standard atmospheric pressure as noted.
a) Describe what is happening in each interval (A-B, B-C, C-D, D-E). Include breathing
movements, muscle movements, etc. that would result from the pressure changes shown.
Connections between Respiratory and Circulatory System
Deoxygenated blood
carrying waste CO2 from
our tissues from cellular
respiration (remember?
Glucose + O2  CO2 + H2O +
ATP (energy)) is returned
to the heart through the
veins, enters the Right
Atrium and enters the right
ventricle which pumps it
through the pulmonary
artery to the lungs. There
the blood and alveoli
exchange waste CO2 and
O 2.
Now the oxygenated blood returns to the heart through the pulmonary vein to the Left Atrium
then enters the Left Ventricle which is a massive muscle that pumps the oxygenated blood to
the rest of the body through the aorta.
The waste CO2 that was picked up by the alveoli is now exhaled.
 Answer questions #8, 9, 10 pg. 254
Respiratory Volumes and Spirographs
p. 250
Normally your regular breathing does not use the full capacity of your lungs, so when you need
more O2 you can increase the volume of air you take into your lungs. Using a spirometer, an
instrument that measures your respiratory volumes, a spirograph can be made demonstrating
the amount of air moving in and out of your lungs with each breath.
Using p. 250 define the following and locate each volume on the spirograph above
Tidal volume:
Inspiratory reserve volume:
Expiratory reserve volume:
Vital capacity:
Vital capacity = _________________________ + _____________________________________ +
________________________
Residual volume:
Using the above information determine the following volumes:
 A normal breath
mL.
 The inspiratory reserve volume
 The inspiratory capacity
mL.  The expiratory reserve volume
 Vital capacity
+
+
+
=
mL
 Residual volume
mL
mL
 Learning Check: Label 1, 2, 3, 4, 5 using residual volume, tidal volume, vital capacity,
inspiratory capacity, expiratory reserve volume.
 Answer #10 pg. 264
Exchange of O2 and CO2 in External and Internal Respiration
p. 250
 Check out these clips: https://www.youtube.com/watch?v=AJpur6XUiq4 - reviews how O2
gets to alveoli and gas exchange
https://www.youtube.com/watch?v=B-X4_hx6j0w - This clip also explains the links of the
respiratory system with the circulatory system.
• External respiration is the exchange of gases between the alveoli of the lungs and the
blood in the capillaries. Internal Respiration is the exchange of gases between the blood
and the body tissues.
External
Respiration
Internal
Respiration
• Because the walls of the alveoli and the capillaries are only one cell thick, O2 and CO2 can be
exchanged passively by diffusion and facilitated diffusion, along the concentration
gradient (high concentration low concentration which is the same as high pressure
(mm Hg)  low pressure in the diagram above)
• 30% of the O2 transferred is through facilitated diffusion - diffusion with the help of
protein carriers. This speeds up the rate of oxygen diffusion. Diffusion alone does not
always carry enough O2 fast enough to meet our needs.
 Check out this clip https://www.youtube.com/watch?v=AyUtdqiOgCA which discusses
how O2 binds to hemoglobin, and is dissociated and why hemoglobin is so suited for O2
transfer, even in low O2 conditions.
Hemoglobin: Oxygen is carried in the
blood bound to haemoglobin in red blood
cells.
Bicarbonate ion: Most carbon dioxide is
carried as bicarbonate ion (HCO3 -)
dissolved in the blood plasma. When the
blood reaches the lungs the bicarbonate
forms CO2 and H2O and the CO2 diffuses
into the alveoli and is exhaled.
Bicarbonate also maintains the pH of our
blood by acting as a buffer and minimizing
the change in pH in our plasma by binding
CO2 (homeostasis).
CO2 Concentrations in the Blood Initiate the Control of Rate of Respiration
 Check out this clip on the mechanics and brain control of breathing
https://www.youtube.com/watch?v=lr5dDmTASos
• As CO2 levels in the blood rise, the repiratory center in the medulla oblongata and the carotid
arteries detect this rise. The medulla oblongata in the brain stem then stimulates the
diaphragm and intercostal muscles to contract faster, increasing the rate of breathing to get rid
of the toxic CO2.
 Do Investigation 7.b pg. 253 “Carbon Dioxide and the Rate of Respiration.” Complete
the Table and Analysis and Conclusion.
7.3 Respiratory Health p. 256
• Upper respiratory tract infections: tonsillitis and laryngitis
• Disorders of the lower respiratory tract impair delivery of O2 to our cells
• bronchitis, pneumonia, pleurisy, emphysema, cystic fibrosis, asthma, lung cancer.
 Read pg. 256 – 262 and answer the following questions
1. A respiratory disorder in which the walls of the alveoli break down causing less surface area
for gas exchange is called
a. emphysema
b. pneumonia
c. bronchitis
d. asthma
2. All disorders of the respiratory system share which of the following characteristics?
a. They all decrease oxygen delivery to the
tissues.
b. They all involve the formation of
carbaminohemoglobin.
c. They are all caused by environmental factors.
d. They are all virus infections.
3. Briefly describe the following respiratory illnesses: pneumonia, asthma, lung cancer,
emphysema, bronchitis, cystic fibrosis,
Include in your description: the specific part of the respiratory system affected,
cause(s), symptoms, treatment/and or cure.
4. Describe the Heimlich maneuver which is a lifesaving technique for a choking person.
5. Discuss carbon monoxide poisoning.
6. Discuss the purpose of iron lungs.
 C7 Test Prep
 Study the chapter summaries: pg. 242, 247-8, 254, 262 – 263
 Study the checklist
 Take the online practice test