Biology 20 – Respiratory
System
• The air we breathe
consists of nitrogen,
carbon dioxide, trace
gases and valuable
oxygen vital for life. In
humans, the only means
we have of obtaining
oxygen is through the
lungs. Absence of
oxygen for more than
just a few minutes can
result in death.
Breathing
• involves the movement of air between the
lungs and the external environment. The
processes involved in breathing include
both inspiration and expiration.
Breathing is not:
Yawning
- Stretching the facial
muscles
Hiccuping
- Spasm of the
diaphragm
Respiration
• involves all processes related to the
exchange of oxygen and carbon dioxide,
including breathing, gas exchange and
cellular respiration.
– External respiration – involves the
exchange of oxygen and carbon dioxide
between the air and the cells of the lungs.
– Internal respiration – involves the
exchange of oxygen and carbon dioxide
between the blood and the tissue fluids.
– Cellular respiration – involves the
combustion of oxygen to produce ATP and
carbon dioxide in the cells.
Anatomy of the Respiratory
System
Respiratory System Anatomy
• Nasal cavity – filters the air with the help of
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cilia and mucous. It also moistens and warms
the air before it goes to the lungs.
Pharynx – opens from the nasal cavity and
branches into two structures:
Esophagus – muscular tube that moves food to
the stomach.
Trachea – the windpipe which is supported by
C-shaped cartilaginous rings and covered with
ciliated cells and mucous that act as a secondary
filter.
• Epiglottis – a flap of skin that
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covers the opening of the trachea to
prevent food from entering the
lungs while swallowing.
Larynx – voice box, composed of 2
thin sheets of elastic ligaments that
vibrate as air is forced out of them.
These are also called the vocal
cords and are protected by a thick
band of cartilage called the Adam’s
apple.
Bronchi- are two tubes that branch
from the trachea and carry air to
the left and right lungs.
• Bronchioles – smaller
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branches off the bronchi that
become progressively smaller
until they reach the alveoli.
Alveoli – air sacs in the lung
where gas exchange occurs.
Alveoli are covered with a
slippery lipoprotein film called
a surfactant that prevents
the sacs from collapsing and
sticking together. Gases
diffuse in and out of the alveoli
according to concentration
gradients.
• Pleural membranes – thin
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membranes surrounding the
outer surface of the lungs. They
are filled with fluid to reduce
friction between the lungs and
the chest cavity during
inhalation.
Diaphragm – a large sheet of
muscle that separates the organs
of the thoracic cavity from those
of the abdominal cavity. As the
muscle contracts, the diaphragm
flattens decreasing pressure
inside the chest cavity, drawing
air into the lungs. Relaxed, the
muscle is dome-shaped.
• Inter-costal muscles –
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found between the ribs.
As they contract, the ribs
are pulled outward and
upward, increasing the
chest volume and
contribute to inspiration.
http://sprojects.mmi.mcgil
l.ca/resp/anatomy.swf
Breathing Movements
• A pressure difference between the
atmosphere and the chest cavity
determine the movement of gases into
and out of the lungs. Gases, like other
substances, move from higher to lower
concentration or from high pressure to low
pressure.
The diaphragm muscle and the intercostals
muscles control and regulate pressure inside
the chest in two ways:
1. When the muscle contracts, the diaphragm
flattens and the ribcage lifts, increasing the
chest volume, decreasing the pleural pressure.
The result is air moving into the lungs during
inspiration.
2. When the muscle relaxes, the diaphragm
becomes dome shaped and the ribcage falls,
decreasing the volume inside the chest, and
increasing pleural pressure. The result is air
moving out of the lungs during expiration.
Habits of the Heart: The Lungs
Breathing Movements
Gas Exchange and Transport
Dalton’s Law of Partial Pressure – each gas in
a mixture exerts its own pressure, or partial
pressure. The sum of the individual gas
pressures add up to the total pressure. The
partial pressure of oxygen and carbon dioxide
varies in different parts of the respiratory
system.
• Pressure of oxygen in the air = 21 kPa
• Pressure of oxygen in the alveoli = 13.3 kPa
• Pressure of oxygen in the arteries = 12.6 kPa
• Pressure of oxygen in the capillaries = 5.3 kPa
• Transport of Gases in the Blood
• oxygen is only slightly soluble in the blood
(0.3mL / 100 mL), so it must be bound to
hemoglobin to be transported in the blood. As
oxyhemoglobin, the blood can carry 20
mL/100 mL of oxygen. The amount of oxygen
that combines with hemoglobin depends on the
partial pressures of oxygen in the blood and in
the tissues. About 97% of all oxygen is carried
by oxyhemoglobin, and the other 3% is carried
in the plasma of the blood.
• About 9% of the carbon dioxide is carried in the
plasma and 27% is carried as
carbaminohemoglobin (HbCO2), and 64% is
carried as carbonic acid or bicarbonate. This
reaction is catalyzed by the enzyme carbonic
anhydrase. The reaction decreases the
amount of carbon dioxide in the plasma, thus
increasing the rate of diffusion of carbon dioxide
from the cells to the blood. Once the blood is
returned back to the lungs, the concentration of
carbonic acid becomes very high, encouraging
the diffusion of carbon dioxide out of the blood
into the lungs.
Ventilation – air flow in / out of the alveoli
Perfusion – blood flow to the alveoli
http://www.wisconline.com/objects/framz.asp?objID=AP2404
Animations
Regulation of Breathing
• Breathing is an autonomic function that is
controlled by nerves from the medulla oblongata
in the brain. Chemoreceptors detect the
levels of carbon dioxide (acid) and oxygen in the
blood and signal the brain to speed up or slow
down breathing.
1. CO2 receptors – are activated when high
levels of CO2 or H2CO3 are found in the blood.
When these receptors are activated, they send
nerve impulses to the rib s and diaphragm to
increase breathing movements.
CO2 + H2O - H2CO3 - H+ + HCO3+
2. Oxygen receptors – are found in the carotid
and aortic bodies in these arteries. If low
levels of oxygen are detected, a message is
sent to the medulla to increase breathing rate.
Response to Exercise
• Ventilation of the alveoli can increase up to 20
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times with heavy exercise.
Muscles produce more CO2 and consume O2.
The brain receives this information and increases
breathing movements.
Epinephrine is also released, increasing
breathing.
The lung exchanges more CO2 and O2.
The kidney excretes excess acid from the blood.
Breathing Disorders
• Asthma – narrowing of/spasms of the muscles
around the airways in the bronchioles that
restricts oxygen flow.
Asthma
• Bronchitis – inflammation of the bronchioles,
usually caused by a viral or bacterial infection, or
by smoking.
Lung Attack
• Emphysema – is caused by chronic bronchitis
until eventually, alveoli burst and scar tissue
remains which irritate the bronchi.
• Pheumothorax – is collection of air or gas in
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the space surrounding the lungs, often caused
by illness or traumatic injury. Air pressure within
the pleural membranes is too high to allow air to
be drawn in to the lungs.
http://pneumothorax.org/pneumo.nsf/Pneumoth
orax.swf
Coughing - your trachea is covered in cilia (tiny
hairs that prevent debris from entering the
bronchioles. Smoking and exposure to other
pollutants interferes with this process, and
causes irritation and coughing.
BioScope BioScope
• Lung Cancer – the abnormal growth of cells in
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the lung causing a tumour (a group of
cancerous cells).
http://www.davidberman.com/design/canceren.swf
Spirometry – Measuring Lung
Volume
Lung capacity can be measured using a
respirometer.
Lung Capacity Measurements
• Total Lung Capacity – the maximum volume
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your lungs can stretch.
Vital Capacity – the maximum amount of air
that can be exhaled (after deep inhale)
Tidal Volume (500 mL) – the amount of air
inhaled and exhaled in a normal breath
Inspiratory Reserve Volume (3000 mL) – is
the amount of air that can be forcibly inhaled
after a normal inhalation
• Expiratory Reserve Volume (1500 mL) – is
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the amount of air that can be forcibly exhaled
after a normal exhalation
Residual Volume (1000 mL)– the volume of
air left in your lungs when all remaining air is
exhaled.
Inspiratory Capacity – the volume of air that
can be forcible inhaled after a normal exhalation
Functional Residual Capacity (2500 mL) –
the total amount of air left in the lungs after a
normal inhalation
• Applet: review the static volumes
• http://sprojects.mmi.mcgill.ca/resp/spirograph.swf