Respiratory System
Dr. Anderson
GCIT
Basic Concepts
• Surface area is important for diffusion (again)
• Physics of fluids
• Special ways to insure against pathogen
invasion of large mucus membranes (lungs
and sinuses)
Nose and Sinuses
Nose Functions
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Opening for air exchange
Moistens and warms air
Houses sensory (smell) neurons
Filters air going to lungs
Serves as resonating chamber for speech
Mucus Membranes
• Line the interior surfaces of the nasal cavity
– Mucus and defensive compounds (enzymes) are
secreted to destroy trapped pathogens (E.g.
defensins)
– Ciliated epithelia move mucus and trapped
contaminants to the back of the throat where they
are swallowed and digested in the stomach
Nasal Conchae
• Occur laterally from
the lateral walls of the
nasal cavity
– Covered in mucosa
and highly vascular
– This serves to warm
and moisten air and
trap particles that may
be inhaled
Nasal Conchae Epithelia
The Pharynx
• Connects nasal cavity and mouth
• Nasopharynx – (Superior to level of the soft
palate) - only serves to transport air
• Oropharynx – (Posterior to oral cavity) – both
swallowed food and air pass through
• Laryngopharynx – (merging of esophagus and
trachea) serves to separate food and air
Larynx - Function
• Provides a “switching” mechanism between
inspiration and swallowing
• Also houses vocal cords for speech
Larynx
Cartilaginous “box” that
maintains an open airway
– Needs to be rigid – why?
– Epiglottis – fold of
cartilage that closes the
trachea during
swallowing
Voice Production
• Vocal cords are stretched on either side of the
larynx, and vibrate as air passed over them from
the lungs
• Air moves between these vocal cords through a
space called the glottis
• Laryngeal muscles that surround the cartilage
change the pitch of the voice by flexing and
relaxing
https://www.youtube.com/watch?v=y2okeYVclQo
Trachea (Windpipe)
• Passageway for air into the lungs, from the
pharynx
• Rings of cartilage prevent collapse under the
negative pressure of inhalation (rigid, but flexible)
• Trachealis muscle allow the trachea to flex during
inhalation, exhalation, sneezing and swallowing
• Lined with mucosa and cilia which propels
particles towards the throat to be swallowed
Bronchi
• Point at which the trachea bifurcates (right
bronchus is wider, shorter and more vertical)
• No cartilaginous rings, but irregular plates
hold bronchi open
• Very little mucus produced, therefore
pathogens and contaminants removes by
WBCs (macrophages)
Bronchi
• Bifurcates from trachea into lungs
- Further subdivides into secondary, (tertiary, etc.
bronchi) within the lungs
- Bronchioles are 0.1 mm in diameter
- Terminal bronchioles are 0.05 mm in diameter and
lead to the alveoli
Anatomy - Lungs
• Left lung – divided into 2 lobes (superior and
inferior)
– Also has space made to accommodate the heart
(cardiac notch)
• Right Lung – 3 lobes (superior, middle and
inferior)
• Both lungs have sections called
bronchopulmonary segments that are separated
by connective tissue
Basic Anatomy
Alveoli (the respiratory zone)
• Respiratory bronchioles lead to alveolar ducts
which lead to alveolar sacs that make up the
alveoli
– Roughly 300 million alveoli present for gas
exchange
Blood Supply
Alveoli - Structure
• Composed of extremely thin single layer of
squamous epithelial cells, which allows rapid
diffusion of O2 in and CO2 out of the blood
• Also allows the evaporation of water out of
the blood
Alveolar Blood Supply
Physics of Breathing
• Partial Pressure
• Diffusion
• Changes in space vs. pressure
Atmospheric Pressure
• At sea level, air rushes towards areas of
relatively lower pressure and away from areas
of relatively higher pressure
• This difference in pressure changes in the
chest cavity via muscle flexing and resultant
forces in the thoracic cavity
Diaphragm and Intercostals
Diaphragm
• Sheet of muscle that separates the thoracic and
abdominal cavities
• Flexing the diaphragm causes it to drop (inferiorly),
increasing the empty volume of the thoracic cavity
• The resulting negative pressure causes air to rush into
the lungs and fill the negative space (inspiration)
• As the diaphragm relaxes, it rises and increases the
pressure in the thoracic cavity, causing exhalation
Intercostal Muscles
• Contraction of intercostal muscles lifts the rib
cage up (superiorly)
• This flexion serves to “open up” the rib cage
and decreases the pressure inside the chest,
causing air to rush in
Physics of Airflow
• Flow = Change in pressure/resistance
• Look familiar?
• Air is a fluid, just as blood is, and is therefore
subject to the same physical rules
Shouldn’t lungs collapse?
• Elastic nature of lungs causes them to contract
inwards
• Surface tension in alveoli (water tension) tries
to collapse alveoli
• Wouldn’t this be bad?
• How is this avoided?
Pressure Balances
• The outside of the lung (visceral pleura) is
attached via pleural fluid to the parietal pleura
(inside surface of the pleural cavity) keeping
them from collapsing
• This keeps the lungs clinging tightly to the
thoracic wall (parietal pleura), preventing their
collapse
The Pleural Cavity
• The pleural cavity produces pleural fluid
which keeps the walls of the lungs in contact
with the thoracic pleura
Alveolar Surfactant
• Surfactant decreases the tension between
water molecules (breaks the cohesiveness
between molecules)
• Reduces the force trying to pull individual
alveolar walls together
Respiratory Volume and Pulmonary
Function
• Volumes
– Tidal Volume: Amount of air moved in and out
under normal resting conditions
– Inspiratory Reserve Volume: amount of air that
can be inspired forcibly beyond the tidal volume
– Expiratory Reserve Volume: volume that can be
forcibly expired beyond the tidal volume
– Residual Volume: air left in lungs, even after
forced expiration
Gas Physics
• Dalton’s Law of Partial Pressures – gases exert a
pressure in proportion to its concentration in a
mixture
• Air
– 78% N2,
– 21% O2,
– 1% Other gases (CO2, rare gases, etc.)
• Pressure of gas is proportional to its
concentration in a mixture
Henry’s Law
• Gas will dissolve into a liquid at a rate
proportional to its partial pressure and viceversa
– Gas
– Liquid
liquid
gas
• This is what allows for the movement of O2 in,
and CO2 out of the blood
Factors Effecting Gas Exchange Rate
• Pressure Gradients (vary with altitude, etc.)
• Ventilation-Perfusion coupling – must be an
efficient match between the volume of air
reaching the alveoli and the blood flow in
pulmonary capillaries
– This is accomplished via vasoconstriction/dilation
• Thickness and Surface area of Respiratory
Membrane
– Thickening of this membrane can lead to respiration
issues
Oxygen Transport
• O2 primarily carried by hemoglobin in blood
– 4 Heme groups in hemoglobin
Deoxyhemoglobin
Oxyhemoglobin
0
1
2
3
4
(Number of heme groups carrying Oxygen)
Factors Affecting Hemoglobin
Saturation
• Partial Pressure of O2
• Blood pH
• Temperature
Bohr Effect
• Increasing acidity (from increasing levels of
CO2) weaken the bond between hemoglobin
and O2.
– What does this mean? Is this a good or bad thing?
CO2 Transport
• CO2 is transported in
– Plasma (7-10%)
– *Bound to hemoglobin (carbaminohemoglobin) –
binds to amino acids, not the heme molecule
– *as bicarbonate in plasma (via carbonic
anhydrase) and RBC’s (enzyme-mediated in BRC
cytoplasm)
• CO2 loading enhances O2 release (Bohr Effect)
Control of Respiration
• Neural Control
– Medulla Oblongata
• Ventral Respiratory Group (VRG)
– Phrenic and intercostal nerves cause diaphragm and
intercostal contraction
• Dorsal Respiratory Group (DRG)
– Modulate rhythms generates by VRG due to peripheral
stimulation (stretch and chemoreceptors)
• Pontine Respiratory Group (PRG)
– Also modulates breathing rhythm by directing impulses to the
VRG
• Communication between all of these centers
regulates breathing rhythm
Factors Influencing Breathing Rate
• Chemoreceptors – monitor blood pH and O2
levels
– Central (found in brain stem), monitors blood pH
– Peripheral (found in aortic arch and carotid arteries),
monitors CO2, blood pH
•
CO2 in blood (Hypercapnia) =
increased respiration rate
• CO2 in blood (Hypocapnia) =
decreased respiration rate
blood pH =
blood pH =
Higher Brain Respiratory Inputs
• Hypothalamus
– Processes sensory input (rapid chilling and/or
heating, pain, etc.) or limbic input affect breathing
rate
• Cortical Controls
– Respiration rate can be consciously controlled, but
will be overridden by brain stem when CO2 gets
too high
Reflexive Respiration
• Irritants can cause reflexive constriction of
passageways
• Inflation reflex – stretch receptors prevent
lung over-inflation (inspiring too much air)
Respiratory Adjustments
• Exercise - CO2 in blood (Hypercapnia) from
muscle contractions
– However, these are not the stimuli!
• Psychological, cortical, and proprioreceptor input are
the cause (we think)
• Altitude
– Decrease O2 pressure results in lower O2
absorption rates
• Altitude Sickness – headache, nausea, fainting, death?