Physiology Flashcards
Right and left coronary arteries arise from…
the base of the aorta
Coronary venous blood drains via…
the coronary sinus into the right atrium
Special adaptations of the CORONARY circulation
High capillary density
High basal blood flow
High oxygen extraction at rest
How does oxygen extraction differ in the coronary circulation in comparison to the rest of the body?
~75% in comparison to a 25% body average
INTRINSIC mechanisms of coronary blood flow control
Reduced PO2 = vasodilatation Metabolic Hyperaemia (match flow) Adenosine = vasodilatation
EXTRINSIC mechanisms of coronary blood flow control
Metabolic Hyperaemia overrides sympathetic vasoconstrictor nerves = vasodilation (functional sympatholysis)
adrenaline = B2 adrenergic receptor activation = vasodilatation
Where in the cardiac cycle does most coronary blood flow and myocardial perfusion take place?
During Diastole (peak left flow), as subendothelial vessels from the left coronary artery are compressed during systole.
What effect does tachycardia have on coronary blood flow?
reduction of coronary blood flow occurs due to shortening of diastole.
What vessels supply the brain?
Internal Carotids and Vertebral arteries (cerebral flow)
Grey matter is sensitive to hypoxia- what does this cause?
Unconsciousness after only a few seconds
Irreversible cell damage within 3 mins
Special Adaptations of CEREBRAL blood flow
Circle of Willis
Autoregulation
Little effect of sympathetic stimulation
Negligible participation in baroreceptor reflex
Circle of Willis =
Basilar + Carotid (anastomosis)
How is cerebral perfusion maintained when one carotid artery is blocked?
Circle of Willis
Obstruction of branch of main carotid artery would…
deprive a certain area of the brain of oxygen
Two types of Stroke are…
Ischaemic (clotting) and Haemorrhagic (bleeding)
What is the function of autoregulation of cerebral blood flow?
To preserves the cerebral blood flow against changes in MABP.
What range does autoregulation of cerebral blood flow occur within?
60-160 mmHg
What occurs as a result of MABP dropping below 50 mmHg (cerebral flow)?
confusion, fainting, brain damage if not quickly corrected.
Effects of PCO2 on cerebral blood flow
Increased PCO2 = vasodilatation
Decreased PCO2 = vasoconstriction
(this is why hyperventilation can lead to fainting)
Regional Hyperaemia
Blood flow increases to active parts of the brain.
Mechanism unknown- suspected to be associated with potassium efflux.
Hypercapnia
AKA hypercarbia, carbon dioxide retention.
Abnormal elevated levels of CO2 in the blood.
Normal Intracranial Pressure
8-13 mmHg
Cerebral Perfusion Pressure (CPP) =…
MABP - ICP
What effect does increased ICP have on CPP?
Increased ICP decreases CPP and therefore cerebral blood flow
