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1. Pulmonary CirculationCharacteristics Low Resistance /Pressure
The specific structure(s) primarily responsible for the majority of control of resistance in the resting state is controversial.
Resistance more evenly distributed, but majority of resistance is normally on the arterial side (upstream) of the the capillaries.
Thin-walled arterial system
(relatively little smooth muscle)
Vessels are surrounded by bags of gas and flexible interstitial fluid-filled regions
No true arterioles??
Alveolar and extra-alveolar vessels respond to conditions differently
2. Influences on resistance Neural/Humoral: all the same players as in the periphery (but less effective) and a few with more specific actions Serotonin: Arterial side vasoconstriction Histamine: Venular side vaso(veno)constriction ***venous side can become dominant resistance Intravascular Pressure R 1/P