The document discusses the maturation of the respiratory system from 5 weeks gestation to childhood. It describes the 4 stages of lung development: pseudoglandular, canalicular, terminal sac (saccular), and alveolar. During the pseudoglandular stage from 5-16 weeks, the lungs resemble glands and gas exchange is not possible. From 16-26 weeks in the canalicular stage, respiratory bronchioles develop. In the terminal sac stage from 26 weeks to birth, alveoli form but surfactant levels are still low. From 8 months to 8 years in the alveolar stage, true alveoli continue developing and producing surfactant, allowing for efficient gas exchange. Respiratory distress

1. DEVELOPMENT OF
RESPIRATORY SYSTEM
Continue......

2. MATURATION OF LUNG
• It deals with histological & functional
development of the lung.
• Maturation of lung is divided into four stages-
1> Psuedoglandular stage- period- 5-16 weeks of
IUL
2> Canalicular stage- period 16-26 weeks of IUL
3> Terminal sac stage- period 26 week to
birth.(saccular stage)
4> Alveolar stage - period 8 month to childhood .
(8 Years)

3. .

4. Alveolar stage

5. 1- Pseudoglandular Period
(5-16 weeks)
• Developing lungs somewhat resembles an exocrine
gland during this period
• By 16 weeks all major elements of the lung have
formed except those involved with gas exchange
• (Terminal bronchioles are formed, BUT no
respiratory bronchioles or alveoli are present )
• Respiration is not possible at this stage
• Fetuses born during this period cannot survive

6. CANALICULAR STAGE
(16-26 Weeks)
• Each terminal bronchiole divide into 2 or more
Respiratory bronchiole
• Respiratory bronchiole divide into Alveolar
ducts.
• Lung is well vascularised
• Fetus born at this stage may or may not
survive.

7. TERMINAL SAC STAGE(saccular
stage)
( 26 weeks to Birth)• Large number of terminal sacs (primitive alveoli) are formed
• Capillaries bulge into the developing sacs
• Epithelium of terminal sac become very thin (simple squamous)
• Close contact develops between epithelium of sac & capillary to
permit adequate exchange of gases
• Fetus born at this stage survive
• Terminal sac lined mainly by type I alveolar epithelium(Type I
pneumocyte) & few type II alveolar epithelium (Type II
Pneumocyte)
• Type I pneumocyte (very thin or squamous epith.) take part in
gasseous exchange
• Type II pneumocytes secrete SURFACTANT that decrease surface
tension in alveoli.

8. ALVEOLAR STAGE
. (8month to 8 years)
32weeks to 8 years
• Formation of true alveoli more
&more(many)
• Many type II pneumocytes that produce
sufficient amount of surfactant
• Free exchange of gasses occur across the
blood-air barriers ( formed by epithelium of
alveoli and endothelium of capillaries).

9. APPLIED RELATED TO
MATURATION OF LUNG
• RESPIRATORY DISTRESS SYNDROME-
• Seen in premature newborn, due to insufficient
amount of SURFACTANT, So surface tension is high
leading to collapse of alveoli, as a result breathlessness
occur in newborn.
• In this disease ,alveoli of lungs are often filled with
fluid having high protein,which resembles glassy
hyaline membrane. Hence RDS is also k/a HYALINE
MEMBRANE DISEASE.
• NEWBORN with RDS is treated with either artificial
surfactant or glucocorticoids injection (which stimulate
surfactant production)

10. QUESTION
• A baby born at 6 months of gestation is having
trouble breathing. Why?
• Ans--- due to insufficient amount of
SURFACTANT, alveoli collapse—no gasseous
exchange occur
• Sufficient amount of surfactant is produced
after 7 month of IUL, ( alveolar stage)