Special Circulations Flashcards
where does the coronary circulation arise from?
base of the aorta
where does the venous blood from the coronary circulation drain into?
drains via the coronary sinus which then drains into the right atrium
what is the percentage of oxygen extraction by the heart?
75%
what does adenosine do in the coronary arteries?
it is a potent vasodilator and causes vasodilatation
what does a decrease in PO2 in coronary arteries cause?
vasodilatation (as the heart requires a lot of oxygen)
what can cause intrinsic mechanisms to override extrinsic mechanisms of heart physiology?
metabolic hyperaemia (as a result of increased CO, so sympathetic stimulation has to cause coronary vasodilation to meet oxygen demand)
when does most left coronary artery blood flow occur?
during diastole (as during systole the ventricles contract and so compress the left coronary arteries)
what effect does shortening diastole have on coronary blood flow?
it decreases the amount of blood flow can take place in the left coronary artery
what arteries is the brain supplied by?
both internal carotids and both vertebral arteries
where do the vertebral arteries arise from?
subclavian arteries
what are the 2 types of strokes?
haemorrhagic (blood leaks out damaged arterial wall) and Ischaemic (obstructive)
what is the most common type of stroke?
Ischaemic
what happens when there is an increase in PCO2 in the cerebral arteries?
cerebral vasodilation
what is the reason why hyperventilating can lead to fainting?
elimination of CO2, decreased PCO2, therefore cerebral vasoconstriction so lack of blood flow to the brain
what happens in cerebral arteries when MAP drops?
they vasodilate (so that the blood flow can remain constant)
what happens in cerebral arteries when MAP rise?
they vasoconstrict in order to limit the blood flow)
what is the normal intracranial pressure (ICP)?
8-13mmHg
what is the formula for Cerebral Perfusion Pressure?
CPP= MAP- ICP
what is the blood brain barrier impermeable to?
hydrophilic substances eg ions and proteins
where does the pulmonary circulation originate from?
right ventricle
what happens to the pulmonary circulation during hypoxia?
pulmonary vessels vasoconstrict (maintains the PO2)
what is the difference between the pressure in the pulmonary circulation and the systemic circulation?
pulmonary circulation pressure is much lower (right ventricle is pumping against low pressure so is smaller than left)
in skeletal muscle what condition overcomes sympathetic constrictor activity?
metabolic hyperaemia
What does the contraction of muscles do to Venous Return?
Increases it
what is the pathophysiology of varicose veins?
the valves are incompetent and so there is backflow which builds up and the pressure in the superficial veins and then they become dilated and tortuous
what effect do varicose veins have on cardiac output?
none
