It is a lipoprotein mixture present in thin layer of fluid lining the alveoli at the air fluid interface. COMPOSITION It is composed of Apoprotein Calcium ions Phospholipids i.e. dipalmitoyl lecithin Surfactant is secreted by 1. Mainly type II alveolar cells in the lungs. 2. Clara cells, which are situated in the bronchioles. It lowers the surface tension of fluid lining the alveoli. Surface tension is inversely proportional to surfactant concentration. During inspiration surfactant molecules move apart as lungs are expanded and during expiration surfactant molecules become concentrated as lungs shorten. When there is no surfactant, Surface Tension is 50 dynes/cm. when surfactant is present it is 5-30 dynes/cm depending upon the concentration Prevents collapse of lungs Stabilize size of alveoli Surfactant helps to keep lungs expanded. If there is deficiency of surfactant then the pressure of -20 to -30 mm of Hg will be required to keep the lungs expanded Surfactant also helps to keep the alveoli dry and prevent development of pulmonary edema. Surfactant is also helpful in lung expansion at birth. If there is deficiency then there is Respiratory Distress Syndrome. LAW OF LAPLACE: pressure required to keep a hollow viscous distended = 2 T/R Where T is tension and R is radius. During expiration, size of alveoli decreases so R is decreased and if T does not decrease, much higher pressure will be required to keep the alveoli distended. When adequate amount of surfactant is there T also decreases so increased pressure is not required. This prevents the collapse of lungs and also stabilizes the equal size of alveoli Definition: “Compliance is the measure of expansibility or distensibility of the lungs. It indicates with how much ease lungs can be expanded”. Work of Breathing In certain diseases there is increased work of breathing and depending upon the nature of breath there will be specific increase in work of breathing. In asthma there is increase in work of breathing to overcome airway resistance In restrictive lung diseases there is increase work of breathing in both tissue resistance and elastic recoil.

1. SURFACTANT
Source: The Guyton and Hall physiology
Maryam Fida (o-1827)

2. SURFACTANT
 It is a lipoprotein mixture present in thin layer
of fluid lining the alveoli at the air fluid
interface.
COMPOSITION
 It is composed of
 Apoprotein
 Calcium ions
 Phospholipids i.e. dipalmitoyl lecithin

4. SOURCE OF SECRETION OF
SURFACTANT
 Surfactant is secreted by
1. Mainly type II alveolar cells in the
lungs.
2. Clara cells, which are situated in
the bronchioles.

5. RELATION WITH SURFACE
TENSION
 It lowers the surface tension of fluid lining the alveoli.
 Surface tension is inversely proportional to surfactant
concentration.
 During inspiration surfactant molecules move apart as
lungs are expanded and during expiration surfactant
molecules become concentrated as lungs shorten.
 When there is no surfactant, Surface Tension is 50
dynes/cm. when surfactant is present it is 5-30 dynes/cm
depending upon the concentration

6. FUNCTIONS OF SURFACTANT
 Prevents collapse of lungs
 Stabilize size of alveoli
 Surfactant helps to keep lungs expanded. If there is deficiency of
surfactant then the pressure of -20 to -30 mm of Hg will be
required to keep the lungs expanded
 Surfactant also helps to keep the alveoli dry and prevent
development of pulmonary edema.
 Surfactant is also helpful in lung expansion at birth. If there is
deficiency then there is Respiratory Distress Syndrome.

7.  LAW OF LAPLACE:
pressure required to keep a hollow viscous distended = 2 T/R
Where T is tension and R is radius.
During expiration, size of alveoli decreases so R is decreased and if T
does not decrease, much higher pressure will be required to keep the
alveoli distended.
When adequate amount of surfactant is there T also decreases so
increased pressure is not required. This prevents the collapse of lungs
and also stabilizes the equal size of alveoli

8. COMPLIANCE
 Definition:
“Compliance is the measure of
expansibility or distensibility of the
lungs. It indicates with how much
ease lungs can be expanded”.

9. FORMULA
 Compliance is the change in lung
volume per unit change of the
transpulmunory pressure or pleural
pressure.
 Compliance = ∆V/∆P
 Combined compliance of thorax and
lungs is 110ml/cm of H2O
 Compliance of the lungs alone is 200
ml/cm of H2O

12. Measurement of Compliance
 To measure compliance we ask the subject to inspire
and expire in short steps of 50-100 ml. in this way we
measure the transpulmunory pressure.
 Transpulmunory pressure = alveolar pressure – pleural
pressure.
 When alveolar pressure becomes zero i.e. when the
subject is not inspiring or expiring, alveolar pressure is
zero. So transpulmunory pressure becomes equal to
pleural pressure which we can measure by esophageal
method.
 If we remove one lung, compliance becomes half

13. APPLIED PHYSIOLOGY
Increase in Compliance Decrease in Compliance
 Physiological condition: Old
age due to loss of elastic
property of lung tissues.
 2. Pathological condition:
Emphysema
only condition in which there
is loss of membranes and loss
of elastic tissue.
 Decreased compliance
means lungs are difficult to
expand.
 Decreased lung compliance
occurs in fibrosis,
atelectasis, COPD, effusion
, Bony deformities kyphosis,
scoliosis, surfactant
deficiency, respiratory
muscle weakness.

14.  TYPES OF Compliance
1. STATIC COMPLIANCE: Recorded during breath holding.
2. DYNAMIC COMPLIANCE: measured during regular breathing.
3. Specific Compliance: Specific compliance is the compliance per liter
of lung volume.
Specific compliance = Compliance of lungs
Functional residual capacity
Functional residual capacity is the volume of air
present in lungs at the end of normal expiration.
ELASTANCE:
It is reciprocal of compliance. i.e. ∆P/∆V

15. Work of Breathing
 Definition:
 “Work of breathing is the work done
by respiratory muscles during breathing
to overcome the resistance in thorax
and respiratory tract.”

16. WORK DONE BY
RESPIRATORY MUSCLES
 During respiratory processes,
inspiration is active process and the
expiration is a passive process. So,
during quiet breathing, respiratory
muscles perform the work only
during inspiration and not during
expiration

17. Work of Breathing
 During quite inspiration:
 65% of work of breathing is to overcome elastic recoil
tendency of the lungs and this is called the elastic work
or compliance work. Lungs always tend to shorten back.
 28% of work of breathing is to overcome the airway
resistance. Medium and large sized airways offer most
of the airway resistance not terminal bronchioles.
 7 % of work of breathing is to overcome the tissue
resistance

18. Work of Breathing
 In certain diseases there is increased work of
breathing and depending upon the nature of breath
there will be specific increase in work of breathing.
 In asthma there is increase in work of breathing to
overcome airway resistance
 In restrictive lung diseases there is increase work of
breathing in both tissue resistance and elastic recoil.