18. Special Circulations

Question 1

What is the circle of Willis formed by?

Answer 1

Internal carotid arteries and vertebral arteries

Question 2

What is the use of the circle of Willis?

Answer 2

Allows perfusion of all parts of the brain even if a large vessel becomes blocked

Question 3

What effect does K+ have on cerebral blood flow?

Answer 3

Increased brain K+ causes dilation of cerebral blood vessels

Question 4

What effect does adenosine have on cerebral blood flow?

Answer 4

Vasodilation

Question 5

What effect does nitric oxide have on cerebral blood flow?

Answer 5

Blocks the enzyme NO synthase, increases response to stimuli

Question 6

What is the Central Nervous System Ischaemic Reflex?

Answer 6

Last ditch reflex to protect cerebral blood flow when mean arterial pressure is low
Systemic vasoconstriction decreases blood flow to other places in order to preserve cerebral blood flow

Question 7

What is the Cushing Reaction?

Answer 7

Increased pressure (tumour, oedema) at normal BP compresses cerebral blood vessels
Decrease in Cerebral blood flow triggers the CNS ischaemic reflex
This increases brain blood flow
High mean arterial pressure causes baroreflex bradycardia and the heart slows
This causes further oedema

Question 8

When does most of coronary blood flow occur in the left ventricle and why?

Answer 8

During diastole

During systole the left ventricle compresses the blood vessels

Question 9

Are metabolites or nerves more important in control of coronary blood flow?

Answer 9

Metabolites

Question 10

What effect do sympathetics nerves have on splanchnic circulation?

Answer 10

Vasoconstriction which shifts blood to skeletal and cardiac muscle
Escape occurs within a few minutes and circulation returns to normal
Constriction can also mobilise blood from veins

Question 11

What effect do gastrin and CCK have on blood flow?

Answer 11

Increase blood flow my dilating arterioles to allow for digestion