Pathophysiology of infant respiratory distress syndrome (IRDS)
The lungs of the foetus remain collapsed until birth. At birth the infant makes several strong inspiratory efforts and the lungs expand . Surfactant prevent them from collapsing again. But in infants who are born before their surfactant system is functional ,the surfactant deficiency causes the lungs to collapse .(Surfactant is not secreted until between 6th – 7th month of gestation and some it happens even later) This is called infant respiratory distress syndrome ( IRDS ). According to the law of Laplace the smaller the radius the more the tension so in a baby’s alveloli surface
tension is high . Administration of phospholipids alone by inhalation is of little use but administration of bovine surfactant ,which contains both phospholipids and proteins. Has been shown to have encouraging results.
Also , the size and number inclusions in type II cells are increased by thyroid hormones and IRDS is more common and more severe in infants with low plasma levels of thyroid hormones than in those with normal plasma levels .Glucocorticoid hormones also accelerate maturation of surfactant in the lungs . In addition, insulin inhibits SP-A accumulation in cultured human fetal lung tissue , and fetal hyperinsulinisam occurs in diabetic mothers . this may explain the high incidence if IRDS in infants born to diabetic mothers.
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