pulmonary circulation Flashcards
what are the two circulation systems of the lungs?
- bronchial circulation
- pulmonary circulation
what are the two arteries of the circulations
systemic (thicker muscle)
pulmonary
what are features of the pulmonary arteries?
- they have a greater lumen to wall thickeness ratio to give them more compliance
- the pulmonary arteries still need to be elastic to convert the pulsatile flow into continuous flow
compare the pressures of the systemic and pulmonary arteries ?
- the systemic circulation operates at higher pressures
- the pressure gradient drives blood flow
compare the cardiac volume and the volume for the pulmonary and systemic arteries?
- cardiac volume = same on both sides
- volume in systemic is much higher
- less pressure
why is less pressure needed in the pulmonary arteries?
- less distance to cover
compare compliance in pulmonary and systemic arteries:
- compliance is higher in the pulmonary circulation
what are the functions of pulmonary circulation?
- gas exchange
- metabolism of vasoactive substances
- filtration of the blood
describe the gas exchange carried out by pulmonary circulation:
♣ CO2 and O2 are the main exchanged gases.
♣ Pulmonary transit time is 0.75s.
o Gas is usually equilibrated in 0.25s.
how are vasoactive substances metabolised?
♣ ACE is exhibited within pulmonary endothelium.
o ACE can mediate production of ANG-II.
ACE can degrade bradykinin
how is the blood filtered
- The entire circulation is a closed circuit but when things get in, the pulmonary circulation filters the blood before it reaches the systemic arteries.
- This can be bad though, in the case of a pulmonary embolism = death.
- The pulmonary circulation acts as a good defence against emboli heading to the brain to cause a stroke.
what is an embolus?
a ‘mass’ within the circulation that is capable of causing an obstruction.
what is an embolism?
♣ – an ‘event’ characterised by obstruction of a major artery.
what are three examples of pulmonary shunts?
- bronchial circulation
- foetal circulation
- congenital defect
how does the bronchial circulation act as a shunt?
The blood goes through the left side of the heart twice (bronchial and systemic circulations) without getting oxygenated.
how does foetal circulation work?
Has two shunts:
a. Foramen Ovale.
Hole between the left and right atria with low resistance.
b. Ductus Arteriosus.
Between aorta and pulmonary arch. This is because O2 is from mother’s placenta, not the lungs.
how does a congenital heart defect act as a shunt?
Congenital Heart Defect – 2 forms:
- Atrial Septal Defect or Patent Foramen Ovale.
- Ventricular Septal Defect.
what happens when the cardiac output is increased?
- Pulmonary circulation is a low resistance, high capacity circuit at a resting Q of 5Lmin-
- what you might think would happen is because there is an increase in MAP
- this increases hydrostatic pressure which forces fluid out
- this leads to pulmonary oedema
- so pulmonary function does not happen effectively
- however, this does not happen :
because the pulmonary system is low resistance high capacity an increase in CO leads to a small increase in MAP - this is because the pulmonary vessels are distensible so they can stretch
- there is increased perfusion to the hypoperfused capillary beds
- so increase in CO increases perfusion
what happens when ventilation is increased?
- inspiration compresses alveolar vessels and expiration compresses the extra-alveolar vessels
- these vessels affect the changes in resistance
- so the resistance is highest at inspiration and expiration
what is the effect of hypoxemia on systemic vessels?
- this causes vasodilation
what is the effect of hypoxemia on pulmonary vessels?
- vasoconstriction
- when the alveoli are not being ventilated the oxygen levels are very low
- the gases continue to be exchanged until they reach equilibrium
- without a fresh supply of air, they become hypoxic
- at a low pp of oxygen, the pulmonary circulation is going to cause vasoconstriction
how does vasoconstriction of the pulmonary vessels happen?
- oxygen sensitive K channels
- no oxygen causes the K to close
- this decreases K efflux
- the surface moves towards its threshold membrane potential
- then there is depolarization
- which causes an influx of calcium
- causing vasoconstriction
the vasoconstriction of pulmonary vessels in response to altitude:
- there is low pressure of oxygen across the lungs
- so there is vasoconstriction
- so more resistance
- this is good during hypoxia because perfusing unventilated alveolus is wasteful
- so the lack of perfusion is good
when is vasoconstriction in response to hypoxia very useful?
- fetal development
- blood flows down least resistance
- high resistance means the blood flows through shunts
when is vasoconstriction in response to hypoxia very bad?
- in COPD
- reduced alveolar ventilation and air trapping already
- so high resistance might cause heart failure or hypertension
what are the two pressures in the pulmonary fluid balance?
- hydrostatic (pushing)
- oncotic ( pulling)
plasma hydrostatic
interstitial hydrostatic
plasma oncotic
plasma oncotic
what is the interstitial hydrostatic pressure in healthy people
0
what does the lymph system do?
- it drains the excess fluid
- which can’t be pulled back in
- if the fluid accumulates then it causes pulmonary oedema
what are some causes of pulmonary oedema?
- mitral valve stenosis
- hypoproteinaemia
- infection
- cancer
explain how mitral valve stenosis causes oedema?
- increased plasma hydrostatic pressure
explain how hypoproteinaemia causes oedema?
- the oncotic force is less
- so more fluid is in the interstituim so there os oedema
explain how infection causes oedema?
- in infection, there are lots of proteins and blood cells in the fluid
- this means there is a bigger pulling force of water into the interstitium
explain how cancer causes oedema?
- if the lymphatics stop working so cannot clear up excess fluid
- then the fluid is going to build up
