6. The Pleura
• The pleura separates
each lung from the
thoracic wall and other
structures
• Secretes a thin
intrapleural fluid which
lubricates the pleural
surfaces as they
slide past each other
7. Different Pressures
• Atmospheric pressure = 760 mm Hg
• Intra-alveolar pressure - pressure within
the alveoli
• Intrapleural pressure - pressure exerted
within the thoracic cavity /756 mm Hg/
14. Pulmonary surfactant
• A complex mixture of lipids and proteins
secreted by the Type II alveolar cells
• Lowers alveolar surface tension
• Decreases hydrogen bonding at the alveolar
air–water interface
• More crowded in small alveoli
15. Law of LaPlace
The smaller alveolus has a tendency
(without pulmonary surfactant) to collapse and
empty its air into the larger alveolus.
Surfactant avoids this!
16.
17. • Surfactant proteins - synthesized in
polyribosomes, modified in the ER, GA and
stored in lamellar bodies before secretion.
• Surfactant phospholipids - synthesized in the
ER and packaged into lamellar bodies. After
exocytosis of lamellar bodies, it’s organized
into tubular myelin
18. Alveolar interdependence
When an alveolus in a group of alveoli collapses, the
surrounding alveoli are stretched. As the other alveoli
recoil in resistance, they pull outward on the collapsing
alveolus.
22. Anatomical Dead Space
Not all the inspired air
gets down to
the alveoli. Part
remains in the
conducting airways,
where it is not
available for gas
exchange. The volume
averages about 150 ml.
24. Gas transport
• Oxygen is present in the blood in two forms:
physically dissolved and chemically bound to
hemoglobin
• Deoxyhemoglobin/oxyhemoglobin
• The saturation, measures the Hb combined
with O2 and can vary from 0% to 100%.
• PO2 of the blood determines saturation
28. Components of neural control of
respiration
1. Factors that generate respiratory rhythm
2. Factors that regulate the magnitude of
ventilation
3. Factors that modify respiratory activity to
serve other purposes.
29. Medullary Respiratory Center
• Dorsal respiratory group consists of inspiratory
neurons. When active inspiration occurs.
• Ventral respiratory group is composed of
inspiratory neurons and expiratory neurons.
Activates when demands for ventilation are
increased.
32. Hering–Breuer reflex
Prevents overinflation of the lungs. Pulmonary
stretch receptors’ action potentials travel
through afferent nerve fibers to the medullary
center and inhibit the inspiratory neurons.
36. Other ventilation factors
• Protective reflexes such as sneezing and
coughing
• Inhalation of noxious agents triggers cessation
of ventilation.
• The expression of various emotional states,
such as laughing, crying, sighing.
• Hiccups
• The respiratory center is reflexly inhibited
during swallowing