| Category | Pulmonary circulation | Systemic circulation |
| Anatomy |
Thin vessels Minimal smooth muscle Vessels are dependent on alveolar pressure (surrounted by intrathoracic air), and expand by radial traction as the lung expands |
Thick vessels Abundant thick smooth muscle Vessels are embedded in tissues |
| Blood volume | About 500ml, in a 70kg person | About 4500ml, in a 70kg person; of which the majority is in capacitance vessels |
| Reservoir function | Contains about 10% of the total blood volume | Contains about 90% of the total blood volume |
| Blood flow | = cardiac output (~ 5 L/min) | = cardiac output (~ 5 L/min) |
| Blood pressure |
Normal PA systolic pressure = 18-25 mmHg Normal PA diastolic pressure = 8-15 mmHg Normal mean pulmonary arterial pressure = 9-16 mmHg |
Normal systolic pressure = 120 mmHg Normal diastolic pressure = 80 mmHg Normal mean arterial pressure = 90 mmHg |
| Circulatory resistance |
Low resistance; Trans-pulmonary intravascular pressure gradient is around 10 mmHg Most of the pressure drop occurs between pulmonary arterial and pulmonary venous capillaries |
High resistance; Trans-systemic intravascular pressure gradient is around 100 mmHg Most of the pressure drop is due to resistance in the systemic arterioles |
| Circulatory regulation | Minimal capacity to actively regulate flow, except via hypoxic pulmonary vasoconstriction | Regional bloodlflow regulation occurs at the level of arterioles |
| Regional distribution of blood flow |
Blood flow is affected by
Little active regulation occurs |
Signficant variation of organ-specific regional blood flow, depending on organ demand Blood flow is less affected by gravity |
| Response to hypoxia | Vasoconstriction | Vasodilation |
| Response tohypercapnia | Vasoconstriction | Vasodilation |
| Gas exchange functions | Absorption of alveolar oxygen; release of capillary carbon dioxide | Release of capillary oxygen; absorption of carbon dioxide by deoxyhaemoglobin |
| Metabolic functions | Metabolism of -hydroxytryptamine, prostaglandins and substrates for angiotensin-converting enzyme (bradykinin and angiotensin I) | Delivery of metabolic substrates to organ systems, and removal of metabolic wastes |
| Synthetic functions | Source of thromboplastin and heparin, which act to degrade filtered clots | Synthesis of nitric oxide, as well as pro-- and anti-coagulants |
| Role in acid base homeostasis | Facilitates CO2 elimination, thereby adjusting acid-base balance | Facilitates washout of lactate and metabolic wastes, thereby adjusting acid-base balance |
| Filter function | Filters emboli larger than 8 μm |
Filtration of arterial blood in the renal and heptic vascular beds results in the clearance of metabolic wastes and particles. |
Chamarthy, Murthy R., Asha Kandathil, and Sanjeeva P. Kalva. "Pulmonary vascular pathophysiology." Cardiovascular diagnosis and therapy 8.3 (2018): 208.