SURFACTANT

Q. A neonate born 4 hours ago is having difficulty breathing. The baby was born at 28 weeks’ gestation. He is tachypneic and is fl aring and grunting. The baby’s heart rate is 120/min, blood pressure is 100/60 mm Hg, and respiratory rate is 55/min. What is this baby’s lung lacking?
(A) Angiotensin-converting enzyme
(B) Collagen
(C) Dipalmitoyl phosphatidylcholine
(D) Elastase
(E) Functional cilia

Ans: C.

This baby was born prematurely, and therefore his lungs have not fully developed. Type II pneumocytes in the lungs are responsible for secreting surfactant (dipalmitoyl phosphatidylcholine). Additionally, a lecithin:sphingomyelin ratio <2.0 is associated with a greater risk of neonatal respiratory distress syndrome. This baby is showing signs of neonatal respiratory distress syndrome due to the lack of surfactant.

Answer A is incorrect. Angiotensin-converting enzyme (ACE) is found primarily in the lungs but is also present throughout the body. ACE is a key enzyme involved in the renin-angiotensin system and converts angiotensin I to angiotensin

II, a potent vasoconstrictor. However, it is not associated with neonatal distress syndrome.

Answer B is incorrect. Collagen is an important part of the connective tissues in lungs. However, it is not associated with neonatal respiratory

distress syndrome.

Answer D is incorrect. Elastase is an endogenous proteolytic enzyme in the lung that is normally broken down by α1-antitrypsin. In patients with α1-antitrypsin deficiency, however, there is an increased level of elastase, which leads to

lung tissue destruction and emphysema.

 Answer E is incorrect. Cilia dysfunction may result in decreased mucus clearance from lungs and predispose patients to recurrent respiratory infections that can cause increased respiratory distress

Table 35–2 Approximate Composition of Surfactant.

Component  Percentage Composition  Dipalmitoylphosphatidylcholine 62 Phosphatidylglycerol 5 Other phospholipids 10 Neutral lipids 13 Proteins 8 Carbohydrate 2

Source: Ganong Physiology.