1. Respiration: Oxygen inhaled and carbon dioxide exhaled
2. Reservoir for the left ventricle: Pulmonary circulation is a blood reservoir for the left ventricle. Even when cardiac output changes this reservoir volume remains constant (about 600 ml)
3. Filter for systemic circulation: Pulmonary circulation filters particles and prevents them from getting to the systemic circulation and causing blockages, particularly blockages in capillaries in the heart and brain. Filtered particles include:
- Blood clots
- Fat cells
- Platelet aggregates
- Debris found stored blood
- Debris found in IV fluids
4. Metabolism: Mainly of bioactive substances
5. Storage and synthezising: Of Heparin, histamine, bradykinin, serotonin and certain prostaglandins
6. Conversion: Angiotensin converted to its active form by the lungs
7. Inactivation: Adenosine Triphosphate (ATP) adn norepinephrine are partially removed from blood and inactivated by the lungs.
The later two functions are particularly important to maintaining homeostasis.
Source: Egan: Fundamentals of Respiratory Care