Editing Respiratory system (section)

====Contributions to whole body functions====
The lung vessels contain a [[Fibrinolysis|fibrinolytic system]] that dissolves [[Blood clots|clots]] that may have arrived in the pulmonary circulation by [[embolism]], often from the deep veins in the legs. They also release a variety of substances that enter the systemic arterial blood, and they remove other substances from the systemic venous blood that reach them via the pulmonary artery. Some [[prostaglandin]]s are removed from the circulation, while others are synthesized in the lungs and released into the blood when lung tissue is stretched.

The lungs activate one hormone. The physiologically inactive decapeptide [[angiotensin I]] is converted to the [[aldosterone]]-releasing octapeptide, [[angiotensin II]], in the pulmonary circulation. The reaction occurs in other tissues as well, but it is particularly prominent in the lungs. Angiotensin II also has a direct effect on [[Arteriole|arteriolar walls]], causing arteriolar [[vasoconstriction]], and consequently a rise in [[arterial blood pressure]].<ref>{{Cite journal|title = Cellular Mechanism of Vasoconstriction Induced by Angiotensin II It Remains To Be Determined|journal = Circulation Research|date = 2003-11-28|issn = 0009-7330|pmid = 14645130|pages = 1015–1017|volume = 93|issue = 11|doi = 10.1161/01.RES.0000105920.33926.60|language = en|first1 = Hideo|last1 = Kanaide|first2 = Toshihiro|last2 = Ichiki|first3 = Junji|last3 = Nishimura|first4 = Katsuya|last4 = Hirano|doi-access = free}}</ref> Large amounts of the [[angiotensin-converting enzyme]] responsible for this activation are located on the surfaces of the [[endothelial cells]] of the alveolar capillaries. The converting enzyme also inactivates [[bradykinin]]. Circulation time through the alveolar capillaries is less than one second, yet 70% of the angiotensin I reaching the lungs is converted to angiotensin II in a single trip through the capillaries. Four other peptidases have been identified on the surface of the pulmonary endothelial cells.