Different circulations Flashcards
where do the right and left coronary arteries arise from?
from the aorta immediately above the aortic valve cusps in dilations called the sinuses of Valsalva
what do the left arteries supply?
the left ventricle, inter ventricular septum
what do the right arteries supply?
right ventricle but distribution varies
how is venous blood drained?
95% via the coronary sinus into the right atrium
5% into the cardiac chambers through the anterior coronary and Thebesian veins
how long is the coronary circulation? in secs
mean transit time is 6-8 seconds
special task of coronary circulation
must deliver oxygen at a high rate to match the basal myocardial demand which is 20x that of skeletal muscle
must increase during exercise
structural adaptations
myocardial capillary density is very high to create a large endothelial SA and reduce maximum diffusion distance
myoglobin stores O2 within cardiac myocytes
exercise training increases coronary artery width and number of arterioles and capillaries
functional adaptations
endothelial NO helps maintain high basal flow
eNOS inhibitors reduce flow by 60%
FA extraction is high, glucose extraction is unusually low, thus fatty acids are the preferred substrate
metabolic hyperaemia is the dominant flow of vascular regulation, with flow increasing linearly with oxygen consumption
sympathetic vasomotor activity maintains high vascular tone
systole obstructs coronary blood flow
explain metabolic hyperaemia
myocardial release of vasodilator substances in proportion to work rate
includes adenosine, H202, H+ and interstitial K+
explain sympathetic vasomotor activity
adrenaline is released
acts upon beta 1 adrenergic receptors in the muscle
increases strength of contraction and rate of contraction
b2 receptors on vascular coronary myocytes result in vasodilation increasing coronary flow
explain how systole obstructs coronary blood flow
2/3 of the coronary arterial system is within the myocardium (intramural) so systole compresses the vessels, especially during the isovolumetric phase
full flow is only restored in diastole
thus coronary perfusion is driven chiefly by diastolic blood pressuree
why are beta blockers useful for heart failure?
increase the length of diastole and thus the time for good perfusion
range of blood flow in skeletal muscle
5-10ml/min/100g of tissue at rest
250ml/min/100g during maximal aerobic exercise
what is the relationship between work rate and oxygen consumption?
linear, the more work done, the more oxygen used, the more muscle blood flow
special task of skeletal muscle
during exercise, circulation must increase to match oxygen consumption due to the increase in work.
skeletal muscle constitutes 40% of body mass and thus its resistance has a huge effect on total peripheral resistance and helps regulate arterial BP
structural adaptations of skeletal muscle
capillary density varies dependent on the muscles activity, postural muscles are always active so have a dense capillary network compared to phasic muscles
endurance training stimulates angiogenesis via growth factors
functional adaptations of skeletal muscle
vascular tone of resistance vessels is high at rest evident by the 50-100 fold increase in vascular conductance in active muscle
basal tone is non neural in origin
muscles are regulated by the baroreflex that senses arterial BP
metabolic vasodilation of resistance vessels increases and sustains blood flow,
arteriolar dilation due to NO recruits more capillaries
during intense activity, muscle fibres switch to anaerobic metabolism
venous muscle pump enhances perfusion during exercise by intermittent compression of deep veins int he calf, forcing blood out the veins and driving capillary perfusion during relaxation
what organ is the least tolerant of ischemia
the brain
explain blood vessels of brain
cerebral arterioles are short, thin walled
large cerebral arteries account for the high fraction of vascular resistance with high autonomic innervation
special tasks
grey matter has a very high rate of oxidative metabolism and is exquisitely sensitive to hypoxia, so the primary task is to maintain O2 delivery at all costs
how does the brain safeguard its blood supply?
the blood brain barrier
