Cardiovascular Circulations

Question 1

What are the two circulations to the lungs and what are their uses

Answer 1

Bronchial circulation - meets metabolic requirements of the lungs

Pulmonary circulation - required for gas exchange

Question 2

What are the pressures in the ventricles, atria, pulmonary artery and aorta

Answer 2

RA - 0-8

RV - 15-30/0-8

Pulmonary artery - 15-30/4-12

LA - 1-10

LV - 100-140/1-10

Aorta - 100-140/60-90

Question 3

What are the two features of the pulmonary circulation

Answer 3

Low pressure

Low resistance - short, wide vessels. Many capillaries.

Question 4

What are the adaptations that promote efficient gas exchange in the lungs

Answer 4

High capillary density in alveolar wall

Short diffusion distance - thin layer of tissue

Question 5

What is the V/Q ratio and what is it needed for

Answer 5

The vetilation - perfusion ratio

Needed to maintain efficient oxygenation

Question 6

What does the lung do to maintain a high V/Q ratio and what is this called

Answer 6

Diverts blood from alveoli that are not well ventilated to other areas

Use the hypoxic pulmonary vasoconstriction

Question 7

What is hypoxic pulmonary vasoconstriction

Answer 7

Where alveolar hypoxia results in vasoconstriction of pulmonary vessels so that poorly ventilated alveoli are less well perfused to optimise gas exchange

Question 8

What effect can chronic hypoxic vasoconstriction cause and why

Answer 8

Can cause RV failure

Chronic hypoxia causes a chronic increase in vascular resistance

This increases the afterload on the RV as it is having to pump against a higher resistance

This causes RV hypertrophy which can then lead to RV heart failure

Question 9

How does gravity affect pressure in the lungs while in the postural position

Answer 9

Causes there to be a greater hydrostatic pressure on the vessels in the lower part of the lungs

This means the vessels near the top (above the heart) collapse during diastole while those near the bottom become distended due to the increased hydrostatic pressure

Question 10

What is the effect of exercise on pulmonary flow

Answer 10

Increased cardiac output - reduces capillary transit time

Increase in pulmonary arterial pressure

Opening of apical capillaries

Question 11

What causes a pulmonary oedema and give some examples of how it can be caused

Answer 11

An increased capillary pressure

Arterial and venous pressure increases cause an increased hydrostatic pressure which results in more fluid leaving forming an oedema

Can be because of an increase in left atrial pressure due to mitral valve stenosis or LV failure

Question 12

How do you treat a pulmonary oedema

Answer 12

Use diuretics to relieve symptoms

Treat underlying cause

Question 13

Why does a large proportion of the cardiac output go to the cerebral circulation and how is it specialised to meet this requirement

Answer 13

Due to the high oxygen consumption by the grey matter

Cerebral circulation has:

High capillary density

High basal flow rate

High oxygen extraction

Question 14

How is a secure cerebral blood flow ensured

Answer 14

Anastomoses between basilar and internal carotoid arteries

Myogenic autoregulation

Metabolic facotrs control blood flow

Brainstem regulates other circulations

Question 15

What does myogenic autoregulation ensure and how

Answer 15

Ensures that the cerebral blood flow is maintain when the BP changes

Increased BP causes vasoconstriction while decreased BP causes vasodilation

Is a response to changes in transmural pressure

Question 16

How does metabolic regulation maintian a secure cerebral blood flow

Answer 16

Vessels are very sensitive to changes in arterial P_CO2

Hypercapnia causes vasodilation to perfuse the area more

Hypocapnia causes vasoconstriction to perfuse the area less

Question 17

What metabolites cause vasodilation of cerebral arterioles

Answer 17

Increased P_CO2

Increased [K⁺]

Increased Adenosine

Decreased PO2

Question 18

Which reflex is activated when there is an increased intracranial pressure impairing cerebral blood flow, what does it do and what can causes the increased pressure

Answer 18

Cushing’s reflex

Impaired blood flow to vasomotor control regions increases sympathetic vasomotor activity causing an increased BP and helps maintian cerebral blood flow

Cerebral tumour or haemorrhage can cause increased pressure

Question 19

Where do the left and right coronary arteries arise

Answer 19

Right and left aortic sinuses

Question 20

When does the majority of blood flow occur in the left coronary artery and why

Answer 20

Occurs mainly during diastole due to increased pressure during systole by the force of muscle contraction making it harder for blood to flow through coronary artery

Question 21

Describe the coronary artery circulation and what local metabolites cause vasodilation

Answer 21

High capillary density with the capillaries being continuously perfused

Continous NO production by coronary endothelium maintians high basal flow

Vasodilators - adenosine, increased [K⁺], decreased pH

Question 22

What type of arteries are coronary arteries and why is this an issue

Answer 22

They are functional end arteries meaning there are few arterio-arterial anastomoses

Means they are prone to atheromas and obstruction by thrombuses

Question 23

Describe the featues of the skeletal muscle circulation

Answer 23

Capillary density depends on muscle type - postural muscles have higher density

High vascular tone

Only half of capillaries are perfused at rest - allows for increased recruitment

Opening of precapillary sphincters allows more capillaries to be perfused

Question 24

What agents act as vasodilators during metabolic hyperaemia

Answer 24

Increased K

Increased osmolarity

Inorganic phosphates

Adenosine

Increased H

Adrenaline on B2 receptors

Question 25

What is the special function of the cutaneous circulation and how is this achieved

Answer 25

Temperature regulation

Acral/apical skin has artereovenous anastomoses which open to increasd blood flow to veins where heat can then be lost - under neural control (SNS)

Non-apical skin has sweat glands which release bradykinin by sympathetic stimulation causes vasodilation to increase heat loss