Session 8.1

Question 1

What are the two circulations of the lungs?

Answer 1

Bronchial circulation

• part of systemic circulation
• meets metabolic requirements of the lungs

Pulmonary circulation

• required for gas exchange
• works at low pressure and low resistance

Question 2

What are the features of the pulmonary circulation?

Answer 2

Low pressure

Low resistance

• short, wide vessels
• lots of capillaries (lots of different routes = less resistance)
• arterioles have relatively little smooth muscle

Question 3

What adaptations are there for efficient gas exchange?

Answer 3

• high density of capillaries =large SA
• short diffusion distance
• narrow capillaries

Question 4

What’s the ventilation perfusion ratio?

Answer 4

For efficient oxygenation, need to match ventilation of alveoli with perfusion of alveoli
Optimal V/Q ratio = 0.8
Maintaining this means diverting blood from alveoli which aren’t well ventilated

Question 5

How can the V/Q ratio be maintained?

Answer 5

Hypoxia pulmonary vasoconstriction

• alveolar hypoxia leads to constriction of pulmonary vessels
• this ensures perfusion matches ventilation
• poorly ventilated alveoli are less well perfumed
• helps optimal gas exchange

Question 6

What are the downsides of hypoxia pulmonary vasoconstriction maintaining V/Q ratio?

Answer 6

• If chronic, can cause right ventricular heart failure
• chronic can occur at altitude or as a consequence of lung disease such as emphysema

If high pressure is consistent = RV hypertrophy and RV heart failure

Question 7

What’s the effect of exercise on pulmonary blood flow?

Answer 7

• Increases cardiac output
• Small increase in pulmonary arterial pressure
• Opens apical capillaries
• Increased o2 uptake by lungs
• As blood flow increases capillary transit time is reduced

Question 8

How does gravity influence pulmonary vessel pressure?

Answer 8

Upright = greater hydrostatic pressure on vessels in the lower part of the lung below the level of the heart
Will be distended during diastole as a result

Question 9

How does low capillary pressure prevent pulmonary oedema?

Answer 9

Lower hydrostatic pressure = less fluid leaves capillaries

Question 10

How can mitral valve stenosis cause pulmonary oedema?

Answer 10

• harder for blood to flow from LA to LV = increased pressure in LV = more pressure in pulmonary veins = pulmonary oedema

Can also get left ventricular failure

Question 11

What are the effects of Pulmonary oedema?

Answer 11

Impairs gas exchange

• affected by posture
• forms mainly at base when upright
• forms throughout lung while lying down (patient often sleeps with several pillows)
• use diuretics to relieve symptoms
• treat underlying cause if possible e.g if caused by mitral valve stenosis, treat than

Question 12

What is the high o2 demand in the brain met by??

Answer 12

High capillary density
High basal flow rate
High o2 extract

Question 13

Why is a supply of O2 to the brain essential?

Answer 13

• neurones sensitive to hypoxia
• loss of consciousness after a few seconds of cerebral ischaemia
• begin to get irreversible after 4 mins
• cerebral infarction = stroke

Question 14

What is the role of myogenic autoregulation in the brain?

Answer 14

Maintains perfusion during hypotension
Increased blood pressure = vasoconstriction
Decreased blood pressure = vasodilation

Fails if BP falls below 50mmHg

Question 15

How is cerebral blood supply secured by metabolic regulation?

Answer 15

Cerebral vessels v sensitive to changes in arterial Pco2
Hypercapnia = High Pco2 = vasodilation so region of brain is better perfumed
Hypocapnia = Low Pco2 = vasoconstriction

Panic hyperventilation can cause hypocapnia and cerebral vasoconstriction leading to dizziness or fainting

Question 16

How does regional activity in the brain influence blood flow?

Answer 16

Areas with increased neuronal activity have increased blood flow

Vasodilation =
Increased Pco2
Increased k+
Increased adenosine

Question 17

What is cushings reflex?

Answer 17

• Rigid cranium protects brain but doesn’t allow volume for expansion
• Increases in intracranial pressure impairs central blood flow = cerebral tumour/haemorrhage
• Impaired blood flow to vasomotor activity = increase arterial BP and helps maintain cerebral blood flow

Question 18

Where do the right and left coronary arteries arise from?

Answer 18

The right and left aortic sinuses

Question 19

What are the adaptations for an efficient coronary circulation?

Answer 19

• high capillary density
• short diffusion distance
• continuous production of NO by coronary endothelium = maintains high basal flow

Question 20

What vasodilators are used for coronary arteries?

Answer 20

Adenosine, increased potassium, lower ph

Question 21

Coronary arteries are functional end arteries. What does this mean?

Answer 21

Prone to atheromas
Narrowed = lead to angina on exercise
Blood flow is mainly during diastole and if HR increased diastole reduced
Stress and cold can cause sympathetic coronary vasoconstriction and angina
Sudden obstruction by thrombus can cause myocardial infarction

Question 22

What does opening of pre capillary sphincters allow?

Answer 22

More capillaries to be perfumed = increases blood flow and reduced diffusion distance

Question 23

What is the role of the Cutaneous circulation?

Answer 23

Temperature regulation
Skin is the main heat dissipating surface, regulated by cutaneous blood flow

Also role in maintaining BP
Vasoconstriction here is to maintain BP

Question 24

What are arteroveous anatosomes?

Answer 24

In the apical skin
a separate bridge between venue and arteriole end of the blood vessel
Can be constricted/dilated

Question 25

How do arterovenous anatasomes regulate heat loss from the apical skin?

Answer 25

• high surface area to volume ratio in skin
• AVA are under neural control, not metabolites
• decrease core temp increases sympathetic tone in AVA = decreased blood flow to apical skin
• increased core temp opens AVAs
• reduced vasomotor drive to AVAs allows them to dilate = diverts blood to veins near surface