Special Circulations Flashcards
Special adaptations of coronary circulation
High capillary density
High oxygen extraction so extra O2 cannot be supplied by increasing extraction
Extra O2 only supplied by increasing coronary blood flow
Intrinsic mechanisms
Decrease in O2 causes vasodilatation
Metabolic hyperaemia matches flow to demand
Adenosine is a vasodilator
Extrinsic mechanisms
Coronary arterioles supplied by sympathetic vasoconstrictor nerves BUT OVER-RIDDEN BY METABOLIC HYPERAEMIA = sympathetic stimulation causes dilatation
Circulating adrenaline activates B2 receptors causing vasodilatation
Peak left coronary flow occurs
during diastole
most coronary blood flow occurs
during diastole
Brain is supplied by
internal carotids and vertebral arteries
Special adaptations of cerebral circulation
Basilar and carotid arteries anastomose to form Circle of Willis
Major cerebral arteries arise from Circle of Willis
Stroke is caused by
interruption of blood supply to region of the brain
Haemorrhagic Stroke
Bleeding
Blood leaks out of artery wall which is damaged
Ischaemic Stroke
Blood clot
Forms an atheroma on artery wall
Blood can’t pass through
Autoregulation of cerebral blood flow
Keeps between 60-160 mmHg
If MABP rises, vessels constrict to limit blood flow
If MABP falls, vessels dilate to maintain blood flow
MABP below 50 mmHg
results in confusion, fainting and brain damage
Increase in pCO2
Vasodilation
Normal intracranial pressure (ICP)
8-13 mmHg
Cerebral perfusion pressure (CPP)
MAP - ICP
