• A complex mixture of lipids and proteins
secreted by the Type II alveolar cells
• Lowers alveolar surface tension
• Decreases hydrogen bonding at the alveolar
• More crowded in small alveoli
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!
• 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
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
• Oxygen is present in the blood in two forms:
physically dissolved and chemically bound to
• The saturation, measures the Hb combined
with O2 and can vary from 0% to 100%.
• PO2 of the blood determines saturation
This reaction takes place slowly in the plasma,
but it’s catalyzed by erythrocyte enzyme
Removing O2 from Hb increases the ability of
Hb to pick up CO2 and CO2-generated H ion
Components of neural control of
1. Factors that generate respiratory rhythm
2. Factors that regulate the magnitude of
3. Factors that modify respiratory activity to
serve other purposes.
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
A region located near the end of the medullary
respiratory center. Displays pacemaker activity.
Prevents the inspiratory
being switched off.
Prevents overinflation of the lungs. Pulmonary
stretch receptors’ action potentials travel
through afferent nerve fibers to the medullary
center and inhibit the inspiratory neurons.
• Responds to
Other ventilation factors
• Protective reflexes such as sneezing and
• Inhalation of noxious agents triggers cessation
• The expression of various emotional states,
such as laughing, crying, sighing.
• The respiratory center is reflexly inhibited