Breathing and exchange of gasses

Question

Which of the following changes does

not occur when a fetus is delivered

and begins to breathe on its own for

the first time?

1. the rate of blood flow through

pulmonary circulation

decreases

2. the foramen ovale closes

3. the ductus arteriosus closes

4. the resistance to blood flow

through the lung decreases

Answer 1

When a newborn takes its first breath, several rapid changes occur in circulation. The lungs expand, pulmonary vessels open, and resistance in the lungs decreases, allowing much more blood to flow through the pulmonary circulation. At the same time, the increased left atrial pressure helps functionally close the foramen ovale, and higher oxygen tension triggers constriction of the ductus arteriosus (though both structures take longer to close completely).

For that reason, the one change that does not occur is a decrease in pulmonary blood flow. In fact, pulmonary circulation increases dramatically at birth to allow oxygen exchange.

Correct answer: 1. the rate of blood flow through pulmonary circulation decreases.