Pulmonary Circulation

Question 1

what are the two physical circulations in the lungs?
where do they & occur from?
what do they drain into?

Answer 1

1. pulmonary circulation
   - Arises from Right Ventricle.
   - Receives 100% of right heart cardiac output.

• *2. bronchial circulation:** supplies blood to the tissues of the bronchi and bronchioles
• Arises from the aorta.
• Part of systemic circulation.
• Receives about 2% of left ventricular output
• right bronchial vein drains into azygous vein, left bronchial vein drains into the hemiazygous and accessory hemiazgous vein

Question 2

what exists between the pulmonary and bronchial circulation? why do they exist?

Answer 2

There are arterial and venous anastomoses (shunts) between the bronchial and pulmonary circulations. These are important ‘safety valves’ to prevent too high a pressure in the pulmonary circulation

Question 3

what is the difference in pressure between pulmonary and systemic circulation?

Answer 3

• Blood pressure much lower in pulmonary circulation c.f. systemic circ

systolic pressure much greater in systemic arteries and capillaires c.f. pulmonary; BUT mean venous pressure is similar for both

Question 4

what ar special anatomic features of pulmonary circulation vessels? (4)

Answer 4

1. Pulmonary arteries: thin walled. They have far less smooth muscle than systemtic arteries
2. They have a larger diameter than systemic arteries
3. Vessels are highly distensible and compressible
4. Because of high compliance, pulmonary arteries stretch during systole. This allows the pulmonary arteries to maintain a low systolic pressure (

Question 5

how does right cardiac output match the left cardiac output, but the pulmonary circulation has less pressure? :)

Answer 5

Then pulmonary vascular resistance R needs to be much lower than systemic vascular resistance for the cardiac output to be same on both sides of heart.

Question 6

what condition do you get if pulmonary vascular pressure increases?

Answer 6

Pulmonary arterial hypertension (PAH): lifethreatening condition

(causes rise in back pressure in right ventricle, which has thinner walls, so dilates - cant pump = right heart failure)

Question 7

what is the innervation like for lungs? basic role?
vertebral level?

Answer 7

• somatic innervation: provides pain and touch sensation from lungs (particularly in pleura) to spinal cord - T2-T6
• sympathetic innervation: innervates smooth muscle of bronchi and small pulmonary vessesls. T2-T4/6

- parasympathetic innervation:
i) vagal afferent fibres detect irritants in airways
ii) vagal efferent fibres produce bronchoconstriction and stimulate secretion of mucous.

Question 8

explain the symapethic innervation to lung a bit more?

pathway?

innervate?

activation causes? how?

Answer 8

sympathetic innervation: T2-T4/6

- The postganglionic nerves from the paravertebral sympathetic ganglia pass into the lungs in plexi around pulmonary arteries and arterioles.

• The sympathetic fibres innervate: smooth muscle within the walls of bronchi and small pulmonary vessels –> form plexi around the BV

- Activation: bronchodilation via beta 2 receptors. Bronchial muscle relaxation due to sympathetic nerves is greatly augmented by circulating adrenaline

Question 9

Bronchial muscle relaxation due to sympathetic nerves is greatly augmented by circulating what????

Answer 9

Bronchial muscle relaxation due to sympathetic nerves is greatly augmented by circulating adrenaline

Question 10

what are J receptors?
where found?
stimulated by?
causes?

Answer 10

J receptors:

• location: alveolar walls
• stimulated by: enlargement of pulmonary capillaries / pulm. oedema
• causes: brachycardia, hypotension

Question 11

parasympathetic vagal afferent & vagal efferent innervation causes what?

Answer 11

parasympathetic:
vagal afferent - triggers cough reflex (due to irritants)
vagal efferent innervation - narrowing of bronchi and mucous production

Question 12

pre-ganglionic nerve fibres (both SNS & PNS): ? (NT and receptor)

parasympathetic post-ganglionic nerve fibres on airway smooth muscle and mucous glands: ? (NT and receptor)

Answer 12

pre-ganglionic nerve fibres (both SNS & PNS): Ach & Nicotinic receptors

parasympathetic post-ganglionic nerve fibres on airway smooth muscle and mucous glands: Ach & M3 (muscarinic receptors)

Question 13

how does gravity influence pulmonary circulation?

whats the 3 zone model?

Answer 13

pressure is much lower in apex c.f. base when standing:

• pulomonary artery: 15mmHg
• pulomonary base: 2 mmHg
• pulomonary apex: 25 mmHg

Creates a 3 zone model of the lung:

•The apices (zone 1) have intermittent flow; capillaries are squashed during expiration and diastole. flow occurs during systole (& inspiration)

•The centres (zone 2) have pulsatile flow; the pressure inside the capillay is greater for part of the resp. cycle: therefore is pulsatile. flow in this part of lung greater in systole than diastole; and inspiration c.f expiration

•The bases (zone 3) have continuous flow of blood; due to pulmonary A & V pressure > alveolar pressure

Question 14

what is lung compliance?

(when is breathing least hard?)

why is low lung compliance bad? (caused by?)

why is high lung compliance bad?

Answer 14

Lung compliance (C) is a measure of ‘stretchability’ or ‘distensibility’ of the lungs. It is the change in the volume per unit pressure change.

C = dV/Dp

breathing least hard when: given change in pressure gives large change in volume. (takes a lot of effort to get that v. last bit of breath in / out during inspiration / expiration - which is where it curves on the graph

Low compliance: requires more effort to inflate lungs - e.g. fibrosis

high lung compliance: if very high, then lungs have lost elastic recoil, so have to have extra effort to exhale. then can take extra effort to inhale again

Question 15

Answer 15

Question 16

what is difference in compliance in base v apex of the lung? what does this mean for ventilation in apex and base?

Answer 16

Compliance in base: higher - this means the base of the lungs are better ventilated (per unit lung volume) than apices.

Compliance in apex: lower

The basal alveoli are more ventilated than apical alveoli, as they have a higher compliance (as shown by a steeper sloping in the curve) and thus a bigger volume change per unit pressure change

Question 17

SO - what is ventilation AND blood flow (perfusion) like in base v apex?

which (ventilation or blood flow) shows a steeper decline with height of lung?

Answer 17

- blood flow and ventilation are higher at the base of the lungs c.f apex

• blood flow (Q on graph) shows a steeper decline with height than ventilation

At the base, blood flow is greater than ventilation yet at the apex, blood flow is worse than ventilation

Question 18

what does ventilation / perfusion ratio graph show?

(what would ideal ratio be? - what is it at base and apex )

what does that mean regarding relationship of perfusion and ventilation in apex and base

Answer 18

• ideal V/Q ratio: 1 for maximally efficient pulmonary function.
• • the ratio is roughly 3.3 in the apex of the lung,*
• • and only 0.63 in the base.*

@ the apex: ventilation exceeds perfusion - bad blood flow, good gas exchange
@ the base: perfusion exceeds ventilation - good blood flow, poor gas exchange

Question 19

how do u work out ventilation / perfusion ratio?

Answer 19

= V/Q

Question 20

what does it mean if V/Q is > 1 ?
what does it mean if V/Q is <1 ?

Answer 20

if V/Q is > 1: ventilation exceeds perfusion - bad blood flow, good gas exchange
if V/Q is <1: perfusion exceeds ventilation - good blood flow, poor gas exchange

:

Question 21

In conditions of airway obstruction V/Q ratio is ?? than normal

In conditions of blood flow obstruction (eg from an embolus) V/Q ratio is ?? than normal.

Answer 21

In conditions of airway obstruction V/Q ratio is LOWER than normal

In conditions of blood flow obstruction (eg from an embolus) V/Q ratio is HIGHER than normal.

Question 22

* important !! *

which, out of ventilation or perfusion, regulates the other? what does this mean, if have hypoxia?

e.g.

If ventilation is reduced in one alveolus, then the capillaries around it ??? , and blood is redirected to ?? ??? alveoli.

Answer 22

local ventilation regulates local perfusion

called: v/q matching

hypoxia: causes vasoconstriction of the local blood vessels

If ventilation is reduced in one alveolus, then the capillaries around it constrict, and blood is redirected to better ventilated alveoli.

Question 23

what happens to pulmonary circulation during exercise?

Answer 23

- pulmonary arterial pressure: increases only slightly during exercise.
- pulmonary arterial resistance: greatly decreasing during exercise (by dilating)

Question 24

what is the mechanism of pulmonary arterial vasodilation during exercise?

1. in the apex of the lung?
2. in the base of the lung?

Answer 24

in the apex of the lung:

• A small pressure increase in pulmonary arterial pressure produces a disproportionately large increase in blood flow.
• The pulmonary arterioles in zone 1 become distended (stretched) when the pressure in them rises: This stretching generates a reflex extra relaxation of the arterial smooth muscle and so the vessels enlarge , reducing the vascular resistance and increasing the flow through zone 1.

Blood flow through zone 1 can increase seven to eight fold during exercise
A similar reflex stretch induced relaxation occurs in zone 2 and 3, where blood flow can increase 2 to three times

• *in the base of the lung:**
• normal base alveoli in the lungs are relatively poorly ventilated during quiet breathing. Thus the associated capillaries are constricted.
• The increased ventilation that occurs at the start of exercise: increases PO2 in these alveoli.
• This dilates the associated capillaries and thus reduces total pulmonary vascular resistance

Question 25

what happens to Arterio-venous shunts in the lungs during exercise?

Answer 25

Arterio-venous shunts **open in the lungs during exercise,** allowing blood to **go directly into the pulmonary veins.** *(this is more of a ‘safety valve’ mechanism, as shunted blood will not be oxygenated). Shunts can also open between the pulmonary and bronchial circulations.*