Special Circulations Flashcards
what is the coronary circulation?
right and left coronary arteries which arise from the base of the aorta
how does coronary venous blood drain?
most via the coronary sinus into the right atrium
why does the coronary circulation require special adaptations?
oxygen demand of cardiac muscle is high especially during exercise
what happens during coronary heart disease?
an area of cardiac muscle is deprived of blood supply due to a coronary vessel being blocked
describe the special adaptations of the coronary circulation
high capillary density
high basal blood flow
high oxygen extraction
how can extra O2 be supplied to the cardiac muscle?
by increasing coronary blood flow
describe the intrinsic mechanisms controlling coronary blood flow
a decrease in po2 causes vasodilation of the coronary arterioles
metabolic hyperaemia matches flow to demand
adenosine (from ATO) is a potent vasodilator
describe the extrinsic mechanisms controlling coronary blood flow
coronary arterioles are supplied by sympathetic vasoconstrictor nerves
but overridden by metabolic hyperaemia as a result of increased HR and SV
so sympathetic stimulation of the heart results in coronary vasodilation despite vasoconstrictor effect
circulating adrenaline activates B2 adrenergic receptors which causes vasodilation
when does peak left coronary flow occur and why?
during diastole as the subendocardial vessels from the left coronary artery are not compressed
what happens when diastole is shortened eg a very fast HR?
there is a decrease in coronary flow
what supplies blood to the brain?
internal carotids and vertebral arteries
which part of the brain is very sensitive to hypoxia?
grey matter
what forms the circle of willis?
basilar and carotid arteries
what forms the basilar artery?
the two vertebral arteries
what is stroke caused by?
interruption/ cut off blood supply to a region of the brain
what is the purpose of autoregulation of cerebral blood flow?
it guards against changes in cerebral blood flow if MAP pressure changes within a range
does sympathetic stimulation and baroreceptors reflex have a big effect on the cerebral circulation?
NO!!!
autoregulation of cerebral blood flow is more important than sympathetic nerve stimulation
describe the autoregulation of cerebral blood flow
If MABP rises, resistance vessels automatically constrict to limit blood flow
If MABP falls, resistance vessels automatically dilate to maintain blood flow
when does autoregulation fail?
if MABP falls below 60mmHg or rises above 160mmHg
what happens if MABP is below 50mmHg?
confusion, fainting and brain damage if not corrected quickly
what happens if there is an increase in PCO2 in the cerebral blood flow?
cerebral vasodilation
what happens if there is a decrease in PCO2 in the cerebral blood flow?
cerebral vasoconstriction which is why hyperventilation could lead to fainting
what happens if there is an increase in intracranial pressure?
there is a decrease in cerebral perfusion pressure and cerebral blood flow
what is the blood brain barrier?
the very tight intercellular junctions in the cerebral capillaries
what happens in the pulmonary circulation?
entire CO flows from right ventricle into it
how are the metabolic needs of the airways met?
systemic bronchial circulation
describe the special adaptations of the pulmonary circulation
pulmonary capillary pressure is low
absorptive forces exceed filtration forces which protects against pulmonary oedema
hypoxia causes vasoconstriction of pulmonary arterioles to help divert blood from poorly ventilated areas of lung
why is resting blood flow low in the skeletal muscle circulation?
because of sympathetic vasoconstrictor tone
what happens to the skeletal muscle blood flow during exercise?
it increases
local metabolic hyperaemia overcomes sympthetic vasoconstrictor activity
circulating adrenaline causes vasodilation
there is also an increase in CO which could contribute
describe the skeletal muscle pump
large veins in limbs lie between skeletal muscles
contraction on muscles aids venous retuen
one way venous valves allow blood to move towards the heart
what is the benefit of the skeletal muscle pump?
reduces the chance for postural hypotension and fainting
