Predominant constituent of Hyaline membrane disease is :
**Core Concept**
Hyaline membrane disease, also known as respiratory distress syndrome (RDS), is a condition that affects premature infants. The disease is characterized by the presence of hyaline membranes in the lungs, which are composed of cellular debris and fibrin. The pathophysiology of RDS is related to the immaturity of the surfactant system in the lungs.
**Why the Correct Answer is Right**
The predominant constituent of hyaline membranes in RDS is fibrin, a protein that is produced by the coagulation cascade. The coagulation cascade is activated in the lungs due to the release of tissue factor and other pro-coagulant substances. This leads to the formation of fibrin clots, which accumulate in the airspaces and alveoli, forming the characteristic hyaline membranes. The lack of surfactant, a complex mixture of phospholipids and proteins, also contributes to the pathogenesis of RDS by increasing the surface tension in the lungs, leading to alveolar collapse and atelectasis.
**Why Each Wrong Option is Incorrect**
* **Option A:** While phospholipids are an essential component of surfactant, they are not the predominant constituent of hyaline membranes.
* **Option B:** Cellular debris is a component of hyaline membranes, but it is not the predominant constituent.
* **Option D:** Surfactant is a complex mixture of phospholipids and proteins, but it is not the predominant constituent of hyaline membranes.
**Clinical Pearl / High-Yield Fact**
The presence of hyaline membranes in the lungs is a hallmark of RDS, and it is often associated with a poor prognosis in premature infants. The use of surfactant replacement therapy has significantly improved the outcome of RDS in premature infants.
**Correct Answer:** C. Fibrin.