pulmonary circulation

Question 1

what are the two circulation systems of the lungs?

Answer 1

• bronchial circulation

- pulmonary circulation

Question 2

what are the two arteries of the circulations

Answer 2

systemic (thicker muscle)

pulmonary

Question 3

what are features of the pulmonary arteries?

Answer 3

• 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

Question 4

compare the pressures of the systemic and pulmonary arteries ?

Answer 4

• the systemic circulation operates at higher pressures

- the pressure gradient drives blood flow

Question 5

compare the cardiac volume and the volume for the pulmonary and systemic arteries?

Answer 5

• cardiac volume = same on both sides
• volume in systemic is much higher
• less pressure

Question 6

why is less pressure needed in the pulmonary arteries?

Answer 6

• less distance to cover

Question 7

compare compliance in pulmonary and systemic arteries:

Answer 7

• compliance is higher in the pulmonary circulation

Question 8

what are the functions of pulmonary circulation?

Answer 8

• gas exchange
• metabolism of vasoactive substances
• filtration of the blood

Question 9

describe the gas exchange carried out by pulmonary circulation:

Answer 9

♣ CO2 and O2 are the main exchanged gases.
♣ Pulmonary transit time is 0.75s.
o Gas is usually equilibrated in 0.25s.

Question 10

how are vasoactive substances metabolised?

Answer 10

♣ ACE is exhibited within pulmonary endothelium.
o ACE can mediate production of ANG-II.
ACE can degrade bradykinin

Question 11

how is the blood filtered

Answer 11

• 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.

Question 12

what is an embolus?

Answer 12

a ‘mass’ within the circulation that is capable of causing an obstruction.

Question 13

what is an embolism?

Answer 13

♣ – an ‘event’ characterised by obstruction of a major artery.

Question 14

what are three examples of pulmonary shunts?

Answer 14

• bronchial circulation
• foetal circulation
• congenital defect

Question 15

how does the bronchial circulation act as a shunt?

Answer 15

The blood goes through the left side of the heart twice (bronchial and systemic circulations) without getting oxygenated.

Question 16

how does foetal circulation work?

Answer 16

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.

Question 17

how does a congenital heart defect act as a shunt?

Answer 17

Congenital Heart Defect – 2 forms:

• Atrial Septal Defect or Patent Foramen Ovale.
• Ventricular Septal Defect.

Question 18

what happens when the cardiac output is increased?

Answer 18

• 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

Question 19

what happens when ventilation is increased?

Answer 19

• 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

Question 20

what is the effect of hypoxemia on systemic vessels?

Answer 20

• this causes vasodilation

Question 21

what is the effect of hypoxemia on pulmonary vessels?

Answer 21

• 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

Question 22

how does vasoconstriction of the pulmonary vessels happen?

Answer 22

• 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

Question 23

the vasoconstriction of pulmonary vessels in response to altitude:

Answer 23

• 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

Question 24

when is vasoconstriction in response to hypoxia very useful?

Answer 24

• fetal development
• blood flows down least resistance
• high resistance means the blood flows through shunts

Question 25

when is vasoconstriction in response to hypoxia very bad?

Answer 25

- in COPD - reduced alveolar ventilation and air trapping already - so high resistance might cause heart failure or hypertension

Question 26

what are the two pressures in the pulmonary fluid balance?

Answer 26

- hydrostatic (pushing) - oncotic ( pulling) plasma hydrostatic interstitial hydrostatic plasma oncotic plasma oncotic

Question 27

what is the interstitial hydrostatic pressure in healthy people

Answer 27

0

Question 28

what does the lymph system do?

Answer 28

- it drains the excess fluid - which can't be pulled back in - if the fluid accumulates then it causes pulmonary oedema

Question 29

what are some causes of pulmonary oedema?

Answer 29

- mitral valve stenosis - hypoproteinaemia - infection - cancer

Question 30

explain how mitral valve stenosis causes oedema?

Answer 30

- increased plasma hydrostatic pressure

Question 31

explain how hypoproteinaemia causes oedema?

Answer 31

- the oncotic force is less | - so more fluid is in the interstituim so there os oedema

Question 32

explain how infection causes oedema?

Answer 32

- 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

Question 33

explain how cancer causes oedema?

Answer 33

- if the lymphatics stop working so cannot clear up excess fluid - then the fluid is going to build up