An impoant non-respiratory function of Lungs:
B i.e. Sodium balance- One of the most impoant metabolic (non-respiratory) function of lungs is activation of relatively physiologically inactive decapeptide angiotensin I to 50 times more potent (active) vasoconstrictor, pressure (TBP), aldosterone stimulating octapeptid angiotensin II by extracellular ACE on the surface of endothelial cells in pulmonary circulation.As a pa of renin - angiotensin-aldesterone system, lungs indirectly regulate sodium and water balance (and BP). However, lungs also directly affect Na+ balaneQ epithelial Na+ channels (E NaCs). Absorption of excess fluid from alveolar lumen and airways require active transepithelial transpo of Na+ by ENaCs (mainly of alveolar type 11 and possibly type I cells.)AR, cystic fibrosis disease is characterized by thick, tenacious and dehydrated airway secretions. In CF, mutations in CFTR (cystic fibrosis trans membrane conductance regulator), which is a regulated CI channel, causes decreased ability to secrete Cl and therefore enhance Na+ and water absorption out of airway. This reduces pericillary fluid and results in thick, sticky and inspissated mucous that cannot be cleared from the mucociliary clearance system l/t recurrent infections.Non-respiratory - Metabolic Functions of LungsFate of biologically biologically active substances metabolized in lungs As Blood reservoir Synthesized & used in- Sutfactant(2 (DPPC)lungs- Proteins collagen & elastin offramework - Carbohydrate mucopolysaccharide ofmucousSynthesized or stored* Histamine& released into the* Arachidonic acid metabolitesblood.- Prostaglandins & Thromboxane Az (byMn-"HAK"cyclooxygenase) - Leukotrienes including SRSA i.e. slowreacting substance of anaphylaxis (byenz. lipooxygenase) * KallikrienActivated in lungs- Angiotensin I is conveed toangiotensin II by ACE.Paially removed from- Norepinephrine (up to 30% is taken upthe bloodby lungs)Mn-"No-BAAPS"- Bradykinin (80% inactivated by ACE) - Acetylcholine - Adenine nucleotide - Protaglandins E1, E2 and F2a (almostcompletely inactivated) - Serotonin (almost completely removedby uptake & storage in platelets andreleased during anaphylaxis)Passed through lungs- Angiotensin Hwithout being- Adrenaline (epinephrine)metabolized- ADH (Vasopressin)(without significant- Prostaglandin (Ai, A2)gain or loss of activity)- Prostacyclin (PGI2)Mn-"DOPA"- Oxytocin - Dopamine & histamine Because lung is the only organ except the hea that receives the whole circulation and has uniquely remarkable ability to reduce its pulmonary vascular resistance by recruitment and distension, it acts as a reservoir for blood.Blood filtrationPulmonary capillary bed acts as a blood filter and remove small thrombi (clots), bubbles, detached cells and prevent them from entering systemic circulation.Fibrinolysis and AnticoagulationLung is rich in mast cells, which secrete anticoagulant heparin. And pulmonary endothelium is rich in plasmin activator, which conves plasminogen into plasmin and promotes fibrinolysis. This is how lungs delay clotting and dissolve small clots (fibrinolysis).Mucosal Immune SystemLungs contribute to defense against infection by secreting immunoglobulin A (IgA). It also has other defense mechanism like- filtration, epithelial barrier, mucociliary clearance, MALT, innate & adaptive immune cells (like alveolar macrophage, NK cells, NK/T cells, dendrite cells, [3 lymphocytes, TCRa(l. and TCR y8 lymphocytes providing humoral & cell mediated immunity)Acid Base Balance, Sodium balance & cooling
Anion balance
Sodium balance
Potassium balance
Calcium balance