AND ITS REGULATION
Prepared by Nixon Dangol
Janaki Medical College and Teaching
Hospital, 11th batch
What is Surfactant?
• These are amphiphilic compounds that
reduces the surface tension of fluid.
• It acts by adsorption into the liquid surface.
The water-insoluble hydrophobic group
extends out of the bulk water phase into the
air, while the water-soluble head group
remains in the water phase. This reduces the
surface tension of the liquid.
• It is the surfactant that lines the alveolar
epithelium. It reduces the surface tension of
water/fluid in alveolar membrane.
• It prevents the collapsing of alveoli
(pneumothorax) and stabilizes alveolar size
and total lung volume.
• Reduction of surface tension also reduces the
oncotic pressure of alveoli that checks the
Biosynthesis of Surfactant
Type II epithelial cells synthesize and assemble the lipid
and protein components into complexes that are
stored as tightly packed membranes in lamellar bodies
until secreted into the alveolar airspace
Lamellar Body Maturation
The alveolar epithelial cell surface is covered by a thin
aqueous layer (hypophase) in which newly secreted,
tightly packed surfactant membranes reorganize to
form a loose network of interconnected membranes
that contacts the air-liquid interface.
unraveling of secreted lamellar bodies to form intermediate
structures such as tubular myelin (TM) or large surfactant
layers that have the potential to move and transfer large
amounts of material to the interface, and
rapid movement of surface active species
through a continuous network of surfactant
membranes, a so-called surface phase,
connecting secreting cells with the interface.
hydration of surfactant complexes, pH, or
Regulation of Surfactant
• Surfactant secretion is regulated locally in the lung by
changes in ventilation rate, possibly mediated by
distension and altered intracellular pH.
• SP-A and dipalmitoylphosphatidylcholine, can inhibit
secretion in vitro, but the mechanism is not known.
• Compression-expansion cycling leads to progressive
conversion of the surface active fractions of surfactant
into much less active lipid/protein complexes. The
alveolar surfactant pool is continuously depleted through
cellular uptake by type II epithelial cells and alveolar
macrophages as well as removal via the mucociliary
escalator. It maintains Surfactant Recycling and