Respiratory system
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Gas exchange
Respiration involves various
processes:
•Ventilation - breathing
•External respiration - gas
exchange between the air and the
blood in the lungs
•Internal respiration - gas
exchange between the blood and
the tissue fluid
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Gas exchange
Gas exchange needs moist respiratory
surfaces to occur.
Aquatic organisms spend up to 25% of the
energies to extract air from water.
Terrestrial organisms need to moisten
constantly the respiratory surfaces.
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Direct respiration through surfaces
Small aquatic animals as cnidarians and plathelminthes
exchange gases directly with the external environment.
4
Branchial respiration
Aquatic invertebrates (mollusks and crustacean) and
vertebrates (fish) have specialized organs for gas
exchange called gills.
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Direct respiration through canals
Insects use tracheae to deliver oxygen directly to
muscles.
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Direct respiration through canals
Terrestrial vertebrates and marine mammals usually moist
air before it enters the lungs.
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Gills
Water moves across the
gills near the mouth. Fish
use countercurrent
exchange to transfer
oxygen efficiently to blood.
Countercurrent
exchange
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Lungs
The respiratory system includes all structures that bring
air to the lungs.
The air is warmed and
humidified in the nasal cavity
and mouth.
The glottis opens and the
trachea connects the larynx to
the two bronchi.
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Bronchioles and
alveoli
Bronchi branch into
bronchioles that end in
alveoli. Alveoli compose
the lung and are the site
for gas exchange with
blood.
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Smoking is dangerous
Short-term effects: nagging cough, diminished
sense of smell, premature aging of the skin.
Long-term effects: cancer, heart diseases,
aneurysm, pulmonary diseases, stroke.
Other effects: chance of premature birth, low birth
weight and stillbirth.
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Inspiration and expiration
Inspiration consists of
muscle contractions that
lower the diaphragm
and raise the ribs. The
negative pressure
causes the air to flow in.
12
Inspiration and expiration
During expiration the
diaphragm muscles relax
and air flows out as the
inner pressure increases.
13
Respiratory centers
Breathing rhythms are
automatically controlled
by the respiratory center
located in the medulla
oblongata, in the
lowermost part of the
brain stem.
Changing in blood pH can
cause variation in the
respiration speed rate.
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Respiration and physical exercise
During exercise the respiratory system makes
adjustments in response to the duration and
intensity of the effort.
During exercises the amount of O2 needed and
CO2 produced increase. Consequently the blood
flow in both muscles and lungs must also increase.
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External and internal respiration
External and internal respiration take advantage
from the spontaneous gas diffusion between air
and blood.
In the lungs the oxygen partial pressure (PO2) is
higher while PCO2 is lower than in the blood.
Hence CO2 diffuses out of the blood into the lungs
and O2 diffuses out of the lungs into the blood.
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Hemoglobin
Hemoglobin (Hb) is a red
blood cells protein involved
in the transport of gases.
External respiration
•Hb combines with O2 to form HbO2.
•HCO3- forms H2CO3 which breaks down into H2O and CO2.
Internal respiration
•HbO2 releases O2 into cells.
•Hb combines with CO2.
•CO2 combines with water to form H2CO3 which then
becomes HCO3-.
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External and internal respiration
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Respiratory disorders
In restrictive pulmonary disorders,
lung capacity is reduced as the lungs
have lost their elasticity.
In obstructive pulmonary
disorders, air does not flow easily in
the airways. Common types are
bronchitis, emphysema and asthma.
Lung cancers are characterized by
thickening and callusing of cells
lining the bronchi, loss of cilia,
formation of a tumor that eventually
metastasizes.
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Online resources
 http://www.abpischools.org.uk/page/modules/breat
hingandasthma/.cfm?coSiteNavigation_allTopic=1
 http://www.wwnorton.com/college/biology/discover
bio5/ch/28/animations.aspx (Structure and Function
of the Lungs; n Oxygen Binding by Hemoglobin)
 http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter25/
animation__gas_exchange_during_respiration.html
 http://www.bbc.co.uk/schools/gcsebitesize/science/
add_aqa/respiration/respirationrev1.shtml
 http://www.bbc.co.uk/schools/gcsebitesize/science/
ocr_gateway/understanding_organisms/fitness_heal
threv1.shtml (page 3)
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