Development of Respiratory System iii maturation of lung

ANATOMY

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)

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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)