My quiestion about ARDS ...?

i took ,, that ARDS has 3 stages ,,, on of these stages is ,, the proliferating phase where the pneumocytes type 2 will proliferate ,,,
and as i know that these cell produce serfactant ,,, and ARDS is due surfactant defiecincy
hence how we can develop ARDS ,, !!!!!

The asnswer to your question lies in the fact that you are confusing an effect with the cause.

ARDS or Acute respiratory distress syndrome usually refers to Neonatal respiratory distress syndrome. This is a disease in newborn infants whose immature lungs cannot produce enough surfactant. The result is collapse of the lung tissue and reduced transfer of gases across the alveolar membrane. Here, the lack of surfactant is the CAUSE of the disease. Usually the child can only be supported with increased ventilatory pressure and synthetic surfactant. In response there is proliferation of pneumocytes and fibrosis of the underlying tissue. This is the EFFECT or response to the injury in an attempt to heal. However it remains that the lung is immaute to begin with and is still unable to produce surfactant until the tissue matures.

By reffering to the 3 stages you are reffering to a disease with similar presentation (respiratory distress) but entirely different situation also called ARDS: i.e. Adult respiratory distress syndrome.
In Adult respiratory distress syndrome an inappropiate response to some injury (chemical, infectious, physical agent etc) results in damage to the alveolocapillary membrane (the lining cells between the air sacs and the blood vessels). This leads to massive leakage of plasma out of the vessels into the air sacs (seen as hyaline protein membranes). This plasma protein rich stuff not only directly interferes with gas exchange but messes up the action of surfactant. Later in RESPONSE to the damage the alveolar sacs show type 2 pneumocyte proliferation.

So in summary you will now be able to differentiate between the two similar sounding but different disease Neonatal and Adult ARDS

Note that in Adult RDS: the cause is alveolar capillary membrane damage and NOT deficency of surfactant (which is the cause of neonatal RDS).

Also note that the proliferation of pneumocytes is a healing response and that despite healing in neonates their cells are still imature and not able to meet the demands of the lung prematurely enforced with the task of breathing. Indeed this is the true cause of neonatal ARDS.

I am glad that you have sought to understand the mechanism of disease. It is the sign of true intellegence in a world when many others are practicing a dangerous method of treating patients. You will make an excellent doctor.

Hope this helps