special circulation Flashcards
where do Right & left coronary arteries arise from
the base of the aorta
where do Most coronary venous blood drain via
coronary sinus into the right atrium
when is Oxygen demand of cardiac muscle high
especially during exercise
what does Coronary circulation requires
special adaptations to help supple the oxygen
what are the Special Adaptations of Coronary Circulation
- High Capillary Density
- High Basal Blood Flow
- High Oxygen Extraction under resting conditions
describe the Intrinsic Mechanisms of Coronary Blood Flow
decreased Po2 causes vasodilatation of the coronary arterioles
Metabolic hyperaemia matches flow to demand
Adenosine (from ATP) is a potent vasodilator
describe the Extrinsic Mechanisms of Coronary Blood Flow:
Coronary arterioles supplied by sympathetic vasoconstrictor nerves BUT
- are 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
Circulating adrenaline activates Beta2 adrenergic receptors, which cause vasodilatation
where are beta 2 receptors found
in the blood vessels
where are beta1 receptors found
in the heart
when does most of the coronary blood flow and myocardial perfusion occur
in diastole when the subendocardial vessels from the left coronary artery are not compressed
what percentage of the adult body is skeletal muscle ~
40% of adult body mass
what does Resistance of skeletal muscle vascular bed impact
it has a large impact on blood pressure
why is Resting blood flow low
because of sympathetic vasoconstrictor tone
what happens during During exercise
- local Metabolic hyperaemia overcomes sympathetic vasoconstrictor activity
- Circulating adrenaline causes vasodilatation (2 adrenergic receptors)
Plus increase cardiac output during exercise, which could increase skeletal muscle blood flow many folds
where do Large veins in limbs lie
between skeletal muscles
what aids venous return
Contraction of muscles
what allows blood to move forward towards the heart
One-way venous valves
what reduces the chance for postural hypotension & fainting
Skeletal muscle pump
varicose veins
Blood pools in lower limb veins if venous valves become incompetent
why do Varicose veins usually not lead to reduction of cardiac output
because of chronic compensatory increase in blood volume
where does the entire cardiac output flow from
right ventricle into pulmonary circulation
how is the Metabolic needs of airways met
by systemic bronchial circulation
what is Pulmonary artery BP typically
20-25/6-12 mmHg
what is Pulmonary capillary pressure
low (~ 8-11 mmHg)
