Special Circulations

Question 1

Where do the right and left coronary arteries arise from?

Answer 1

base of aorta

Question 2

Where does most coronary venous blood drain?

Answer 2

Into right atrium from coronary sinus

Question 3

What are the special adaptations of coronary circulation?

Answer 3

• high basal blood flow
• high capillary density
• high oxygen extraction

Question 4

What is the only way extra oxygen van be supplied in coronary circulation?

Answer 4

by increasing coronary flow, which is controlled by intrinsic and extrinsic mechansims

Question 5

Potent vasodilator

Answer 5

Adenosine from ATP

Question 6

Intrinsic mechanisms of coronary blood flow

Answer 6

Decrease in oxygen saturation causes vasodilation of coronary arterioles, thus metabolic hyperaemia maths flow to demand

Question 7

What nerves supply coronary arterioles?

Answer 7

Sympathetic vasoconstrictor nerves

Question 8

Why does metabolic hyperaemia override sympathetic vasoconstrictive nerve supply?

Answer 8

Due to an increase in HR and SV

Question 9

Functional sympatholysis

Answer 9

Sympathetic stimulation of heart results in coronary vasodilation (due to being overrides by metabolic hyperaemia) despite direct vasoconstrictor effect

Question 10

Extrinsic mechanisms

Answer 10

Adrenaline activate B2-ADR-> vasodilation

Metabolic hyperaemia-> overrides sympathetic vasoconstriction-> vasodilation

Question 11

At what stage does most of the coronary blood flow and myocardial perfusion?

Answer 11

during diastole, when subendocardial vessels from LCA are not compressed

Question 12

What supplies the brain?

Answer 12

Internal carotids and vertebral arteries

Question 13

Which arteries anastomose to form the Circle of Willis?

Answer 13

Basilar (formed by two vertebral arteries) and carotid arteries

Question 14

When does autoregulation come into play?

Answer 14

if MAP changes within the range of around 60-160mmHg (outwith this range, autoregulation will fail and cerebral blood flow will rise/ fall)

Question 15

What happens if MAP rises in autoregulation of cerebral blood flow?

Answer 15

Automatic vasoconstriction

Question 16

What happens if MAP falls below approx 50mmHg?

Answer 16

Results in confusion, fainting and brain damage if not corrected quickly

Question 17

Why can hyperventilation lead to fainting?

Answer 17

a decrease in oxygen saturation causes vasoconstriction

Question 18

Regional hyperaemia

Answer 18

Blood flow increases to active parts of the brain

Possibly because of rise in K+ conc due to K+ efflux from repetitive active neurones

Question 19

Increasing PaO2 _____ cerebral blood flow

Answer 19

increases

Question 20

Normal intracranial pressure

Answer 20

8-12mmHg

Question 21

How to calculate cerebral perfusion pressure

Answer 21

CPP=MAP-ICP

Question 22

Effect of increasing ICP on CPP and cerebral blood flow

Answer 22

Decreases CPP and cerebral blood flow

Question 23

Blood brain barrier

Answer 23

Tight intercellular junctions of cerebral capillaries

Question 24

What substances is the BBB very impermeable to?

Answer 24

hydrophilic substances eg ions, catecholamines, proteins

Question 25

What substances is the BBB very permeable to?

Answer 25

Oxygen and carbon dioxide

Question 26

What helps protect brain neurones from fluctuating levels of ions etc. in blood?

Answer 26

BBB is exceptionally impermeable to hydrophilic substances

Question 27

Average pulmonary artery BP

Answer 27

20/6-25/12mmHg

Question 28

how does pulmonary circulation protect against pulmonary oedema?

Answer 28

absorptive forces exceed filtration forces

Question 29

why does hypoxia cause vasoconstriction of pulmonary arterioles?

Answer 29

It helps divert blood from poorly ventilated areas of lung

Question 30

Why is resting skeletal muscle flow low?

Answer 30

sympathetic vasoconstrictor tone

Question 31

Why does skeletal muscle blood flow increase during exercise

Answer 31

• Local metabolic hyperaemia overcomes sympathetic vasoconstrictor tone
• adrenaline causes vasodilation
• increased CO-> increased skeletal muscle blood flow

Question 32

Varicose veins

Answer 32

Blood pools in lower limbs if venous valves become incompetent, however this doesn’t usually lead to reduced CO due to chronic compensatory increase in blood volume