Biochem PS Flashcards
What is PS?
pulmonary surfactant
A complex mixture of lipids (90%)and proteins (10%) produced alveoli in
within the lung and secreted along the alveolar surface
Where is PS found?
along the air-liquid interface on the surface the alveolar walls
Why is it important?
- Decreases surface tension within the alveoli to prevent
collapse and facilitate respiration
defects in PS production»_space;
increase ST & difficultly w/ respiration.
Gas exchange between air in alveoli( Large moist surface for gas )is by
diffusion
Gas exchange between air in alveoli and erythrocytes in pulmonary capillaries • Via
alveolar type I cell
Gas molecules move
through——-covering alveolar wall
thin fluid layer
alveolar cells epithelial type
squamous
Define surface tension
Film of water along the alveolar wall
tendency
(Force)of liquid surfaces to shrink into the minimum surface area possible.
Describe the mechanism of surface tension
• Cohesion between adjacent water molecules
• Lack of forces pulling water molecules away from fluid at air
interphase creates tension along surface
• Cohesion between adjacent water molecules
- Hydrogen bonding between molecules
- H 2O molecules prefer to interact with each other rather than air
- Minimize surface area
Laplace Law:
P = 2T/r
Attraction and alveolar size
Attraction increases and alveolar size decreases
Cohesive forces result in
increased thickness of this fluid layer
& decrease in overall surface area.
the fluidity of the aqueous layer increase
the amount of P decrease
————-reduce surface tension and prevent collapse of alveoli
Pulmonary surfactants
to reinflate:——- ST
decrease
How does pulmonary surfactant reduce surface tension in alveoli?
because of amphipathic structure
1)Cohesive forces between water molecules pulling them DOWN and
2)Surfactant film neutralizes this effect by creating a new cohesive force pulling UP
• Increases the fluidity of the aqueous layer and reduces the amount of
pressure required to expand alveoli i.e. makes breathing easier
amphipathic structure
Hydrophobic tails interact with gas layer
Hydrophilic polar heads interact with water molecules
Absences of surfactant :
- High surface tension: alveoli collapse on expiration
* Fluid flow from blood to alveolar space (pulmonary edema)
Lipid composition of PS
1)DPPC (dipalmitoylphosphatidylcholine)mainly
2) Unsaturated phospholipids (PC) and
3) neutral lipids like cholesterol
PC= phosphatidylcholine
DPPC
a saturated (single bond) glycerophospholipid with two C16 saturated fatty acyl chains
• Excellent compaction, but pure films ——-at 37℃
lack fluidity
Unsaturated phospholipids (PC) and neutral lipids like
cholesterol
Function
Increase fluidity and surfcant films
What happens in case of excess cholesterol
prevents full activity of surfactant
bcz it is preventing full compaction necessary,and
is often associated with lung injury
How DPPC synthesized?
In cytoplasm
Conversion of Glucose to Dihydroxyacetone phosphate (DHAP)to
Glycerol 3-phosphate and fatty acyl -CoA
From Dihydroxyacetone phosphate (DHAP to glycerol 3-phosphate by
Glycerol 3-phosphate dehydrogenase
Fa tty acid at—- position replaced by palmitic acid (C16)
2
Where does this take place within the cell?
Biosynthesis of pulmonary surfactant
In type 2 alveolar cells Synthesis of the lipid components, matures from RER to the golgi then to MVB, then LB to the extra cellular space.
Pu lmonary surfactant proteins
- Hydrophilic/amphipathic proteins
* Hydrophobic proteins
Hydrophilic/amphipathic proteins mention them
SP-A,
SP-D
Hydrophilic/amphipathic proteins known as
Collectins (Ca 2+ dependent C-type lectins)
Function of amphipathic proteins?
1) Immune function and protection from pathogens
2) Regulation of lipid secretion
Mention the Hydrophobic proteins
SP-B, SP-C
SP-B
lipid associated
SP-C
integral membrane protein
Function of Hydrophobic proteins?
1) Important for the integrity and maintenance of the PS film organization an
2) ability to compress and extend during respiration
SP-A
Characteristics?
1)Large glycoprotein
2)Most abundant surfactant
protein
3)High affinity for DPPC
SP-A
Associated with surfactant
lipids on alveolar surface through
CRD = carbohydrate recognition domain
Function of SP-D
1) Activation of macrophages
2) Agglutination of bacteria
3) Protection against pathogens
4) part of innate immune system (main role)
Hexamers of trimers
SP-A
Tetramer of trimers
SP-D
PS function in immune response
1) Aggregation
2) Opsonization
3) Inhibition of microbial growth
4) increase cell membrane permeability
5) pro- and anti-inflammatory roles
