special circulations Flashcards
(58 cards)
where do the right and left coronary arteries arise from?
the base of the aorta
where does most coronary venous blood drain via?
the coronary sinus into the right atrium
Oxygen demand of cardiac muscle is ___ especially during ___. Coronary circulation requires ______
Oxygen demand of cardiac muscle is high especially during exercise
Coronary circulation requires special adaptations
what are three special adaptations of the coronary circulation?
High Capillary Density
High Basal Blood Flow
High Oxygen Extraction (~75% compared to 25% whole body average) under resting conditions
what does the high oxygen extraction of the coronary arteires under resting conditions mean when further O2 is required?
This means extra O2 (when required) cannot be supplied by increasing O2 extraction
Can only be supplied by increasing coronary blood flow
what is the only way of increased the supply of oxygen to the coronary circulation?
Can only be supplied by increasing coronary blood flow
what are the two types of mechanisms for coronary blood flow control?
intrinsic and extrinsic
what three intrinsic mechanisms are there to increase coronary blood flow?
- decrease Po2 causes vasodilatation of the coronary arterioles
- Metabolic hyperaemia matches flow to demand decreased PO2
- Adenosine (from ATP) is a potent vasodilator
what mechanisms are involved in the extrinsic control of coronary blood flow?
- the coronary arterioles are supplied by sympathetic nerves (causing vasoconstriction)
- also circulating adrenaline activates B2 adrenergic receptors found on cardiac smooth muscle arterioels causing vasodilatation
what intrinsic mechanism over-rides the sympathetic innervation to the coronary arterioles? and how is this done?
metabolic hyperaemia over-rides sympathetic as a result of increased hr and SV.
The effect of sympathetic innervation on the heart causes:
- Decreased local PO2
- Increased local PCO2
- Increased local [H+] (decreased pH)
- Increased extra-cellular [K+]
- Increased osmolality of ECF
- Adenosine release (from ATP)
so
So sympathetic stimulation of the heart results in coronary vasodilatation/constriction despite direct vasoconstrictor effect (functional sympatholysis)
vasodilatation
what are the receptors for sympathetic neurotransmitter signals in the coronry vascular SM? and what is the neurotransmitter?
noradrenaline acting on alpha 1
what does adrenaline act on in coronary SMc?
beta receptors
where are the adrenaline beta receptors found in the body?
in the skeletal and cardiac smooth muscle arterioles
where are the alpha adrenaline receptors found in the body? and what does this cause>
found in the gut, skin, and kidney arterioles and cause vasoconstriction
look at the table in khogali’s special circulations lecture
x
when does most of the left coronary artery filling occur?
during diastole when the subendocardial vessels from the left coronary artery are not compressed
what causes a short diastole period?
a very fast heart rate - so get reduced coronary flow
which main arteries supply the brain?
the internal carotids and the vertebral arteries
why does the brain need a secure supply of oxygen?
Grey matter VERY sensitive to hypoxia - consciousness lost after few seconds of ischaemia, irreversible cell damage within ~ 3 minutes
what forms the basilar arteries?
two vertebral arteries and the carotid arteries
what do the basilar arteries do to improve circulation?
they anastamose to form the circle of Willis
the circle of willis gives rise to?
major cerebral arteries
what does anastamoses ensure?q
Cerebral perfusion should be maintained even if one carotid artery gets obstructed.
