Special Circulations Flashcards
Where do the right and left coronary arteries arise from?
Base of the aorta
Where does most coronary venous blood drain?
Via coronary sinus into the right atrium
What are the two branches of the left mainstem coronary artery?
Circumflex and left anterior descending
What are 3 adaptations of the coronary circulation?
High capillary density, high basal blood flow and high oxygen extraction
What is the only way extra O2 can be supplied to the coronary circulation?
By increasing coronary blood flow
What does decreasing PO2 do to the coronary arterioles?
Vasodilation
What from ATP is a potent vasodilator?
Adenosine
What are coronary arterioles supplied by?
Sympathetic vasoconstrictor nerves
Sympathetic stimulation of the heart results in what?
Coronary vasodilation
How does circulating adrenaline cause vasodilation?
Activates beta 2 adrenoceptors
When does most of coronary blood flow and myocardial perfusion take place?
Diastole
What vessels supply the brain?
Internal carotids and vertebral arteries
Which part of the brain is more sensitive to hypoxia?
Grey matter
What arteries anastomose to form the Circle of Willis?
Basilar artery and carotid arteries
What does the Circle of Willis allow?
Cerebral perfusion to be maintained even f one carotid artery is blocked
What happens to resistance vessels in the cerebral circulation if MABP rises?
Constrict
What happens to resistance vessels in the cerebral circulation if MABP decreases?
Dilate
Autoregulation of cerebral blood flow fails when MABP is outwith what limits?
< 60 or > 160
Increased PCO2 does what to the cerebral vasculature?
Vasodilation
Decreased PCO2 does what to the cerebral vasculature?
Vasoconstriction
What does increases cerebral pressure do to cerebral blood flow?
Decreases it
What makes the tight intercellular junctions of cerebral capillaries?
Blood brain barrier
Cerebral capillaries are highly permeable to what?
O2 and CO2
How does glucose cross the blood brain barrier?
Facilitated diffusion
What is the blood brain barrier impermeable to?
Hydrophilic substances
Where does the entire cardiac output from the right ventricle go?
Pulmonary circulation
What supplies the lungs?
Systemic bronchial circulation
What is the pulmonary capillary pressure compared to systemic capillary pressure?
Low
What does hypoxia do to pulmonary arterioles?
vasoconstriction
Why is resting blood flow of the skeletal muscle circulation low?
Sympathetic vasoconstrictor tone
What overcomes sympathetic vasoconstrictor activity in skeletal muscle?
Metabolic hyperaemia
What does circulating adrenaline do to blood vessels?
Vasodilation
What does contraction of skeletal muscle do to veins?
Squeezes them to aid venous return
What does the skeletal muscle pump reduce the chance of?
Postural hypotension and fainting
What compensatory change does varicose veins cause?
Increased blood volume
