Before birth, the alveoli in a baby’s lungs are expanded and filled by?

Correct option is B

Sol. Before birth, a baby’s lungs are filled with fetal lung fluid, not air. This fluid is secreted by the fetal lung cells and helps in lung development and alveolar expansion. At birth, the fluid is absorbed or expelled during delivery, and air replaces it when the baby takes the first breath. This transition is vital for normal respiration after birth.
Explanation of each option:
· (a) Air – Incorrect. Air enters the lungs only after birth when the newborn takes its first breath. Prenatal lungs do not contain air.
· (b) Fluid – Correct. Fetal lung fluid fills the alveoli before birth, aiding in lung maturation and preparing the lungs for postnatal breathing.
· (c) Blood – Blood circulates around the alveoli (in capillaries) but does not fill them. Its role is to exchange gases, not occupy alveolar space.
· (d) Meconium – This is the baby’s first stool; it should remain in the intestine. Presence in the lungs (due to aspiration) is abnormal and dangerous.