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Respiratory System
Blood Circulation
• Remember, all cells need
oxygen in order to make ATP
– Oxygen is only carried by red
blood cells via hemoglobin, so it
runs out quickest
• Additionally, carbon dioxide is
produced as a waste product
and so must be released from
the blood constantly
– CO2 mixes with water to make
acid so it has to be balanced
Respiratory System
• The respiratory system consists of
the lungs and the air passages that
allow air to reach the lungs
– The lungs themselves have capillaries
that allow gas exchange
• The respiratory system also
includes the diaphragm, the sheet
of muscle that drives quiet
breathing
– Pulls down when contracting, like
pulling a syringe plunger
Respiratory System
Air Passages
• The conducting zone is all of
the respiratory system that
allows air to flow
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Mouth and nose
Nasal Passages
Throat (pharynx)
Larynx
Trachea
Bronchi
Bronchioles
Nasal Passages
• The nasal passages leading
from the nose to the pharynx
have a number of key features:
– Mucous membranes that trap
particles
– Cilia (tiny moving hairs) that
move mucus to the pharynx
– Olfactory epithelium for smelling
– Auditory tube for equalizing
pressure of middle ear
Pharynx and Larynx
• The pharynx carries both
food and air to the trachea
and esophagus
• The top of the trachea is the
larynx (voice box) which
produces speech
– A flap of cartilage called the
epiglottis folds over the larynx
when swallowing to prevent
inhaling food
Trachea
• The trachea is the passage for
air to the lungs
– Anterior to the esophagus
• Held open by C-shaped rings
of cartilage
– The trachealis muscle can
squeeze the back ends of the
ring together, which happens
when you cough
Bronchi and Bronchioles
• The bronchi (singular bronchus)
are the branches of the trachea
– Branch further to make secondary
and tertiary bronchi inside the
lungs
– Reinforced with cartilage
• The bronchi branch further to
make bronchioles
– Not reinforced with cartilage, but
covered in smooth muscle
• Can dilate and constrict
Alveoli
• The bronchioles eventually
become respiratory
bronchioles, part of the
respiratory zone of the lungs
• The bronchioles end in air
sacs called alveoli (singular
alveolus) covered in
capillaries
– This is where gas exchange
occurs
Alveolus Structure
• Alveoli are composed of
simple squamous epithelium
• Lubricated by an alveolar
fluid that includes a
surfactant
– Allows air to pass by water
with less friction
– Premature babies do not yet
produce surfactant so
breathing is very difficult for
them!
Gas Exchange
• Oxygen diffuses into the blood in the lungs and
carbon dioxide diffuses out
– The lungs keep a large storage of CO2 to maintain pH
balance (CO2 + H2O = acid)
– This is why breathing excessively fast
(hyperventilation) can cause you to pass out, since
your blood is becoming too alkaline too fast
Gas Exchange System
Obligatory Smoking References
• Breathing particulate matter
(smoke) in is bad for your lungs!
– Can damage alveoli and obstruct
bronchioles
• Tobacco plants produce a
particularly unpleasant mix of
chemicals including tar and
mutation-causing chemicals
– But on the other hand, nicotine
makes you feel really good (and is
also addictive because it taps into
your dopamine circuits)