Special Circulations Flashcards
right and left coronary arteries arise from the ___ of the aorta.
base
Where does most coronary venous blood drain via and to?
coronary sinus
right atrium
name some special adaptations of coronary circulation
High capillary density
high basal blood flow
High O2 extraction
increasing coronary BF
what is the value of o2 extraction in heart compared with body? What does this mean?
75%
body avg 25%
means extra O2, when required eg exercise cannot be supplied by increasing o2 extraction
coronary BF is controlled via intrinsic/extrinsic mechanisms?
both
d; hyperaemia
excess of blood in organ
describe the intrinsic mechanisms that control coronary BF/
decrease Po2 causes vasodilatation of the coronary arterioles
Metabolic hyperaemia matches flow to demand
Adenosine (from ATP) is a potent vasodilator
describe extrinsic controls of coronary BF
Coronary arterioles supplied by sympathetic vasoconstrictor nerves BUT
Over-ridden by metabolic hyperaemia as a result of increased heart rate and stroke volume
So sympathetic stimulation of the heart results in coronary vasodilatation despite direct vasoconstrictor effect (functional sympatholysis)
Circulating adrenaline activates 2 adrenergic receptors, which cause vasodilatation
what are the two receptors in coronary arteries?
alpha and beta 2
What is the only thing that causes vasoconstriction on coronary arteries?
sympathetic stimulation
when is flow low in CA?
systole
When is there peak BF in LCA?
during diastole
What does shortening diastole do to HR and coronary flow?
very fast HR
decreases coronary flow
When does most of coronary BF and myocardial perfusion occur and why?
occurs in diastole when the subendocardial vessels from the left coronary artery are not compressed
What arteries supply the brain?
internal carotids and vertebral arteries
Why is consciousness lost a few seconds after ischaemia in brain/
grey matter verysensitive to hypoxia
after what time is there irreversible to brain/
after 3 mins
How is stroke caused?
by interruption/ cut off of BS to region of the brain
what pressure range must MAP occur within , whilst its changing, for autoregulation of cerebral BF?
60-160mmHg
What two things have very little effect on cerebral BF?
direct sympathetic stimulation
baroreceptor
reflexes
what happens if MABP rises
resistance vessels automatically constrict to limit blood flow
what happens if MABP falls
resistance vessels automatically dilate to maintain blood flow
Why is the pressure change range of MAP between 60-160mmHG?
Autoregulation fails if MABP falls below ~ 60mmHg (cerebral blood flow falls) or rise above ~ 160mmHg (cerebral blood flow rises)
What does a MAP below 50mmHg result in?
results in confusion, fainting, and brain damage if not quickly corrected
Why could hyperventilation lead to fainting?
increase in PCO2 causes cerebral vasodilation
decrease in PCO2 causes vasoconstriction
How does BF possibly increase to active parts of the brain?
Blood flow increases to active parts of the brain (regional hyperaemia). Mechanism unknown. May be due to rise in [K+]O as a result of K+ efflux from repetitively active neurones?
how much of the brain is blood?
12%
what is normal intercranial pressure ICP?
8-13mmHg
What is the equation for cerebral perfusion pressure CPP?
MAP-ICP
What is effect of increasing intercranial pressure/
Increasing ICP (e.g. due to head injury, or brain tumour) decreases CPP and cerebral blood flow
What are the potential consequences of increasing ICP?
can lead o failure of autoregulation of cerebral BF
what is the tight intercellular junctions between cerebral capillaries called?
blood brain barrier
cerebral capillaries are ______ ________ to O2 and CO2
highly permeable
How does glucose cross the blood brain barrier?
via facilitated diffusion using special carrier molecules
what is the BBB impermeable to?
to hydrophilic substances such as ions, catecholamines, proteins etc
How does the fact brain is impermeable to other hydrophilic substances protect bran?
helps protect brain neurones from fluctuating levels of ions etc in blood
What type of pressure system is pulmonary circulation?
low pressure
What is the typical pressure in a pulmonary artery?
(20-25)/(6-12)
what is the pressure range of pulmonary circulation?
8-11mmHg
what is the pressure range of the systemic capillary pressure?
17-25mmHg
what protects against pulmonary oedema?
absorptive forces exceed filtration forces
What does hypoxia cause in pulmonay arterioles?
vasoconstriction
Hypoxia causes vasoconstriction of pulmonary arterioles. COMPLETELY OPPOSITE TO EFFECT OF HYPOXIA ON SYSTEMIC ARTERIOLES. WHY?
would help divert blood from poorly ventilated areas of lung
what percentage of the body is made up by the skeletal muscle?
40%
What does the resistance of the skeletal muscle vascular bed do to BP?
has large impact on blood pressure
Resting blood flow is low because of sympathetic vasoconstrictor tone
during exercise what overcomes vasoconstrictor activity?
metabolic hyperaemia
also increased CO could increase skeletal muscle BF
what does circulating adrenaline cause to BV and via what?
vasodilation
beta 2 adrenergic receptors
describe the skeletal muscle pump?
Large veins in limbs lie between skeletal muscles
Contraction of muscles aids venous return
One-way venous valves allow blood to move forward towards the heart
Skeletal muscle pump reduces the chance for postural hypotension & fainting
If Blood pools in lower limb veins if venous valves become incompetent, what is this called?
varicose veins
why doesn’t varicose veins not lead to reduction of CO?
because of chronic compensatory increase in blood volume
