Final answer:
The parasympathetic nervous system causes bronchoconstriction and promotes mucus secretion in the lungs, which can lead to narrowing of the airways and might decrease ventilation. correct answer is option A.
Step-by-step explanation:
The autonomic nervous system, which includes the parasympathetic and sympathetic nervous systems, plays a crucial role in the control of airway diameter in the lungs. The parasympathetic nervous system is responsible for bronchoconstriction, which is a decrease in the size of the bronchioles due to the contraction of the muscular wall. This leads to a reduction in the size of the air passageways and can enhance mucus secretion. On the other hand, the sympathetic nervous system causes bronchodilation, an increase in the size of the bronchioles allowing more air to flow into and out of the lungs.
Given the options provided in the question and understanding the role of the parasympathetic nervous system, the correct effect it has on the lungs is B. Mucus secretion. This is because the contraction of the bronchioles' muscles leads to not only narrowing of the airways but also prompts glandular cells to secrete mucus. Hence, parasympathetic activation does not lead to increased ventilation or bronchodilation and might actually contribute to decreased ventilation due to the restriction of airflow.