RESPIRATORY SYSTEM
Ass. Prof. Dr. Emre Hamurtekin
EMU Faculty of Pharmacy
SURFACTANT
SURFACTANT
• Alveolar lining fluid
generates surface tension.
• Strong attraction of water
molecules form the surface
tension.
• Surface tension is a force
forcing the alveoli to
collapse.
• The effect of surface tension
is reduced by surfactant.
• Type II pneumocytes
synthesize and release
pulmonary surfactant.
SURFACTANT
• Surfactant’s main component is a phospholipid which is
dipalmitoyl phosphatidylcholine.
• Stored in lamellar bodies in Type II pneumocytes and
released by exocytosis to the alveolar surface.
• The polar head allows them interact with water molecules
and reduce the surface tension.
• Functions of surfactant:
a)
b)
c)
Stabilizes the alveolar size,
Increases compliance,
Keeps lungs dry.
SURFACTANT
a)
Stabilizes the alveolar size:
Decrease in alveolar volume decreases surface area and concentrates
surfactant molecules which helps reducing the surface tension,
This prevents the collapse of alveoli.
Increase in alveolar volume decreases the density of surfactant and allows
surface tension.
b)
Increasing compliance:
Lung compliance: Amount of pressure needed to inflate lungs to a given
volume.
Surface tension decreases lung compliance.
Surfactant decreases the effort to inflate the lungs.
c)
Keeping lungs dry:
The surface tension produce a driving force for the interstitial fluid to drain into
the alveoli.
Surfactant reduces the pressure gradient and helps keeping the lungs dry
(prevent from pulmonay edema).
BREATHING MECHANICS
• Lung tissue is sealed to the lining of the thoracic cavity.
• Pleurae are thin serous membranes that cover the lungs.
• Parietal and visceral pleura are separated by intrapleural space.
• Pleural fluid is secreted into the intrapleural space.
• Pleural fluid has two functions:
 Lubrication (allows the lungs to slide freely over the chest wall and
diaphragm)
 Aiding inspiration (cohesion allows forces to be transferred directly
to the lung surface)
BREATHING MECHANICS
BREATHING MECHANICS
INSPIRATION:
• Inspiration is an active process.
• When diaphragm contracts, intrathoracic volume
increases.
• Diaphragm contraction:
 pushes downward of the abdominal contents and increases the
vertical dimensions of thoracic cavity
 causes the ribs to rise and cross-sectional area increases.
EXPIRATION:
• Expiration is generally a passive process and is driven by;
Surface tension
Elastic recoil
LUNG MECHANICS
LUNG MECHANICS
• Air flow is inversely proportional to airway resistance.
• Airway resistance is influnced by;
 Airway radius*** (greatest influnce)
 Air viscosity
 Turbulance
• Airway radius:
 Decreases with each generation down the bronchiolar tree.
 As the airway numbers increase, combined resistance decreases with the
increasing branches of bronchioles.
 Larnyx and the larger airways have the greatest airway resistance.
• Air viscosity:
 Air viscosity depends on air density.
 Increasing density increases flow resistance.
• Turbulance:
 Each branch point creates a local vortex current and this increases the
airway resistance.
LUNG MECHANICS
• Factors affecting airway radius:
Smooth muscle
 Autonomic control
 Local factors
Lung volume
• Parasympathetic: reduces airflow
Vagus nerve
Ach
M3 receptor
bronchoconstriction
• Sympathetic: increases airflow
SNS terminals
Norepinephrine
presynaptic β 2-adrenergic receptors
inhibition of Ach release
bronchodilatation
 Local Factors:
 Local irritants and allergens constrict bronchioles and obstruct airways.
 Histamine and other inflammatory mediators mediate airway smooth muscle
constriction.
 Lung Volume:
 Airway resistance is highly dependent on lung volume.
 Net airway resistance is low at high lung volumes, and high in low lung volumes.
WORK of BREATHING
WORK of BREATHING
Elastic Work
Required to;
- counter lung’s elastic recoil during inspiration
(proportional to its compliance)
- displace the chest wall outward and
the abdominal organs downward
- Pulmonary fibrosis increases elastic work.
Resistive Work
Required to;
- move the air through the airways against
airway resistance
- Chronic Obstructive Pulmonary Diseases (COPD)
increases elastic work.