Question

The control of ventilation and perfusion is represented by the following correct order of events:
A. Decreased blood flow to the region of lung
B. Vasoconstriction of pulmonary vessels in that region
C. Decreased pulmonary blood partial pressure of oxygen
D. Decreased air flow to the region of lung
E. Diversion of blood flow and air flow away from the area of disease to healthy areas of lung
Choose the correct answer from the options given below:

• A. D, C, B, A, E
• B. D, C, B, E, A
• C. C, D, B, E, A
• D. D, C, E, A, B

Hint:

Low ventilation → Low O\(_2\) → Vasoconstriction → Blood diverted This maintains proper V/Q matching.

Answer 1

The Correct Option is B

Concept:
Ventilation-perfusion (V/Q) matching ensures optimal gas exchange. When ventilation decreases in a lung region, compensatory mechanisms redirect blood flow.

Step 1: Initial event – decreased ventilation.

• Disease or obstruction leads to reduced airflow Thus: \[ D: Decreased air flow \]

Step 2: Effect on oxygen levels.

• Reduced ventilation lowers oxygen in alveoli Thus: \[ C: Decreased partial pressure of oxygen \]

Step 3: Pulmonary response.
Low oxygen triggers:
• Hypoxic pulmonary vasoconstriction Thus: \[ B: Vasoconstriction \]

Step 4: Redistribution mechanism.

• Blood is redirected to better ventilated regions
• Airflow also shifts to healthier areas Thus: \[ E: Diversion of flow \]

Step 5: Final outcome.

• Reduced blood flow in poorly ventilated area Thus: \[ A: Decreased blood flow \]

Step 6: Final sequence.
\[ D \rightarrow C \rightarrow B \rightarrow E \rightarrow A \] \[ \boxed{\text{Correct answer = Option (2)}} \]