pulmonary circulation Flashcards
outline the basic functions of the PC
- o2/CO2 exchange
- reservoir for blood (capacitance)
- filter
- synthesis and metabolism of vasoactive substances such as ACE
outline the characteristics of the PC
- receives all right V output
- low intravascular pressure - thin wall of RV
- low resistance - short length and large radius
- 8-10 microM radius larger than systemic
- thin walled vessels
- highly distensible
- reservoir function
- huge capillary SA- gas exchange
- can be altered by recruitment, distension and collapse
outline the effects of gravity on the PC
Near the base- pressure in arterial vessels is 40/20mmHg - Distension
Near apex- pressure in arterial vessels and capillaries Is not high enough to hold them open in diastole
- vessels collapse
establishes a gradient for pulmonary perfusion from apex- base
- diffusion increases from apex- base when upright
when supine (lying down)
- pulmonary perfusion is evenly distributed from apex - base
- distention and contain greater blood volume
outline the capacitance function of the PC
- upright, redistributes blood towards base and increases return to LA/LV
- p
outline some mediators of P vasoconstriction?
- increased SNS activity (a1) leads to VC
- exercise reflex - limit P capacity and increase returning of blood to LV= increased CO
- inflammatory mediators - allergens such as histamine, bradykinin and 5-HT
- During episodes of hypoxia
- increases pressure throughout PC
- limits distension of vessels
outline the local effect of hypoxia on PC?
- poor ventilation of alveoli
- VC at this damaged site to reduce blood flow and direct it to a better ventilated area, this aims to improve 02 exchange
- if not widespread- can be advantageous
chronic widespread hypoxia
- diseased state/high alt
- generalised P VC
- increase P in PC leading to pathology and limits o2 exchange
- mechanism of VC involves ROS leading to increases in intracellular Ca In smooth muscle cells
Effects of chronic P VC?
- increase in P vasc R - increases RV work= HF
- pulmonary remodelling - prolonged HP- hypertrophy of V smooth muscle, increases R = HF
increased CHP- increased fluid filtration out of caps - P oedema
leading to impairment of GE between cap/ alveoli
- rise in CHP can lead to interstitial oedema and eventually in the long term alveolar oedema
P oedema occurs in ?
- hypoxia
- inflammation, anaphylactic responses (VC, increased permeability)
- extreme exercise cases (VC)
- LV failure - increase left atrial pressure - feeds back into PC
outline the filter function of the PC
- microthrombi - small particles of RBCs, platelets and fibrin aggregates longe in the PC where they are lysed
- blood clot from DVT can lead to P embolism increasing dead space and blood bypassing of alveoli
metabolic functions
- NO in response to shear stress - tonic P VD
– PGI2 - tonic P dilation
inhalation of both can treat PPH and hypoxia
ACE - ag1- ag2 (VC)
P endothelium removes and degrades 5-HT and Nad
