Coronary and cerebral blood flow Flashcards
Circulatory demands (flow in ml/min-1/100g-1)
Basal. Working
Coronary. 75. 350
Skeletal. 15. >60
Cutaneous. 15. 175 (can be as low as 1ml)
Cerebral. 55. 55
Autoregulation
The tendency of flow to remain constant despite alterations in perfusion pressure
Coronary circulation
Must deliver O2 at a sufficient rate depending on cardiac rate.
V.high capillary density
Large endothelial area
Reduced difusion distance
High flow and O2 extraction
Myocardium can extract upto 90% O2 during exercise (75% normally).
Increased flow - metabolic hyperaemia (main control process)
Metabolic vasodilation can overcome maximal sympathetic stimulation of heartrate.
Factors that increase resistance in coronary circulation
Systolic compression
Myogenic mechanisms
Alpha adrenoceptor stimulation
Factors that decrease resistance in coronary circulation
Adenosine
Vagal nerve stimulation
Beta adrenoceptor stimulation
Cerebral circulation
The brain revieves 14% of cardiac output.
Arteries receive richer autonomic innervation than arterioles.
Grey matter is hupoxia intolerant and has a very high rate of oxidative metabolism.
O2 supply to brain is crucial
Local brajn areas have specific metabolic and flow requirements.
Structural adaptations of the cerebral circulation
Cicrle of Willis - ensures that cerebral nlood flow is preserved even if one carotid artery is blocked.
High capillary density
BBB - tight endothelial junctions
Functional adaptations of the cerebral circulation
High basal blood flow (grey matter), extracts 35% of delivered O2.
Self preservation - controls circulatory system, other than the heart
Cerebral autoregulation - excused from baroreflex, flow maintained within a large range of pressures
CO2 sensitivity - high pCO2 causes profound vasodilation, hyperventilation causes vasoconstriction in retina, disturbed vision, dizzyness, fainting.
Regional hyperaemia.
Parasympathetic and sensory vasodilators.
5HT as a vasoconstrictor
