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Features of pulmonary and systemic circulation

Features of pulmonary circulation
It is a low pressure system
Because it only needs to pump  blood to the top of the lungs.
If it is high pressure, then  following Starling forces, the fluid  would flood  the lungs.
Advantages of Pulmonary Circulation being a Low Resistance system
  • Accommodates more blood as a person shifts from the standing to the lying position.
  • High compliance allows the vessel to dilate in response to modest increase in Pulmonary arterial pressure.
  • Pulse pressure in the pulmonary circulation is rather low
Pressures in the pulmonary system
Right Ventricle:
Systolic= 25 mmHg
Diastolic= 0-1 mmHg,
Pulmonary artery:
Systolic= 25 mmHg
Diastolic= 8 mmHg
Mean Pulmonary arterial pressure= 15 mmHg.
Pulmonary Vein:
Averages about 5 mmHg
Pulmonary capillaries:
7 mm Hg
Left atrium:
Averages 2 mmHg
It is a low resistance system
  • Only 1/10th of the resistance of the systemic circulation
  • Arterioles have less smooth muscle, veins are wider & shorter& pulmonary vessel walls are thinner. 
Pulmonary vasculature has High compliance
  • Accommodates 5 L of blood  (same as the systemic circulation)
  • Accommodates shifts of blood more  quickly e.g. when a person shifts from  a standing to a lying position
Features of systemic circulation
Systemic circulation is a High pressure system
Because it needs to send blood to the brain even when standing & to the tip of en elevated fingertip.
Systemic circulation has High resistance
Because of increased smooth muscle in the  arterioles & the  metarterioles. 
Systemic circulation has Low compliance
Because of resistance  offered by the arterioles  and the metarterioles