<prompt> Non-respiratory function of lungs -Anion balanceSodium balancePotassium balanceCalcium balance  <response>: Ans. is b i.e., Sodium balance One of the most important metabolic non-respiratory function of lungs is activation of relatively physiologically in active decapeptide angiotensin I to 50 times more potent active vasoconstrictor, pressor BP, aldosterone stimulating octapeptid angiotensin II by extracellular ACE on the surface of endothelial cells in pulmonary circulation. Asa part of renin-angiotensin-aldesterone system, lungs indirectly regulate sodium and water balance and BP. However, lungs also directly affect Na balance via epithelial Na channels E NaCs. Absorption of excess fluid from alveolar lumen and airways require active transepithelial transport of Na by ENaCs mainly of alveolar type II and possibly type I cells. 