This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
An impoant non-respiratory function of Lungs is: 
Select and explain. 
A. Anion balance, B. Sodium balance, C. Potassium balance, D. Calcium balance
B: Sodium balance
Answer: B: Sodium balance 
Explanation: Lung has large amounts of angiotensin conveing enzyme which is located on the surface of endothelial cells of the pulmonary capillary. This enzyme conves the inactive decapeptide angiotensin I into aldosterone stimulating octapeptide angiotensin II. This angiotensin II stimulates the production of aldosterone which increase sodium resoption, thereby maintaining sodium balance. Ref: Pulmonary Physiology, Lange Physiology Seires, 6th Edition, Pages 215-226.