Final answer:
Smooth muscle in the lungs helps regulate air flow by allowing the airways to expand and contract.
Step-by-step explanation:
Smooth muscle plays a role in the lungs after birth by helping to regulate air flow. The smooth muscles in the lungs allow the airways to expand and contract as needed. This is important for the process of breathing and the exchange of oxygen and carbon dioxide in the lungs. For example, when we inhale, the smooth muscles relax, allowing the airways to open up and air to flow in. When we exhale, the smooth muscles contract, narrowing the airways and helping to push air out of the lungs.