Special Circulations

Question 1

What is ventilation perfusion mismatch?

Answer 1

When the V/Q ratio is suboptimal

For efficent oxygenation- ventilation and perfusion of alveoli need to match

Question 2

How is the V/Q ratio maintained?

Answer 2

Vasoconstriction of pulmonary vessles to mean poorly ventilated alveoli don’t recieve blood
Opposite effect to systemic circulation

Question 3

What is different in the pulmonary and systemic circulation?

Answer 3

Acts at a lower pressure and reistance

Vasorestriction to poorly perfused tissues

Question 4

How is blood flow through the bain influenced?

Answer 4

Myogenic autoregulation;
Increase in bp- vasoconstriction
Decreases in bp- vasodilation

Maintains a constant blood flow to brain

Maetabolic;
Increase in pco2- vasodilation
Decrease in pco2- vasoconstriction

Cushings reflex;
Pressure on brain stem increases synpathetiv activity
Helps maintian high B flow to brain

Question 5

What are features of cardiac circulation?

Answer 5

High density of of capillaries
Blood flow increases with O2 demand
Coroanry arteries are functional end arteries (blood flow mainly in diastole)

Question 6

What forces are involved in tissue fluid formation?

Answer 6

Outwards hydrostaic pressure
Inwards plasma oncotic pressure
Interstital oncotic pressure

Inceased capillary pressure causes more fluid to move out

Normally pulmonary cap pressure is low to prevent odeama

Question 7

Conswquences of pulmonary odeam?

Answer 7

Impairs gas exchange
Worsens throuhout lungs when lying down

Treat underlying cause
Diuretics treat symptoms

Question 8

What factors influence blood flow through skin?

Answer 8

Artereovenous anastomoses (AVAs) in apical skin- sympa activity controls, if core temp rises they open, diverts blood near surface

Sweat glands (non apical skin) activated by sympa, also released vasodilators

Question 9

What factors influence blood flow through skeletal muscle?

Answer 9

Metabolic hyperaemia (increase in metabolites) act as vasodilators
Adrenaline (via B2 receptors on arterioles)

At rest only half caps perfused- allows increased recruitment
Cap sphincters can open

High vascular tone (allows for dilation)

High cap density (different depending on activity level)

Question 10

What are the normal pressures in the pulmonary circulation?

Answer 10

Pulmonary arterial- 12-15 mmHg
Pulmonary caps- 5 mmHg
Pulmonary veins- 5 mmHg

This is much lower than in systemic due to low resistance