lecture 17 - special circulation Flashcards
Which coronary artery is most commonly involved in an MI?
Left anterior descending
What are the 3 key vessels that coronary venous blood drains to?
Coronary sinus, anterior coronary vein, thebesian vein
Why is there slight deoxygenation of arterial blood?
Because the thebesian vein, draining some of the coronary venous blood, drains deoxygenated blood straight into the left ventricle, where it will be pumped to the circulation bypassing the lungs
Why do cardiac muscle fibres have a much smaller fibre diameter than skeletal muscle fibres?
More capillaries can sit between the fibres and provide the heavy oxygen supply that the myocardium needs by:
- having a big surface area for O2 transfer
- having a short diffusion distance into cardiomyocytes
What is the dominant form of vascular regulation in the myocardium?
Metabolic hyperaemia
How does metabolic hyperaemia alter coronary blood flow?
As the metabolic demand of the heart increases, more metabolites, e.g. adenosine, are produced and O2 drops, which leads to arteriolar dilation which increases blood flow.
What is the O2 extraction in the heart, relative to other tissues?
High - 75% at rest
What is the problem with functional end-arteries as the coronary arteries of the heart?
When the arteries becomes narrowed/a thrombus occurs, there is only one blood supply to the area and death can occur
What are arterio-arterial anastomoses?
Arterial ‘loops’ that allow multiple arteries to supply the same area, meaning if one is compromised the other can compensate (e.g. radial and ulnar arteries)
Which state of the cardiac cycle obstructs coronary blood flow?
Systole
Why does systole obstruct coronary blood flow?
Most of the coronary circulation is in the myocardium, so vessels become constricted as the muscle squeezes in systole
Why does increasing diastolic length with Beta blockers improve MI recovery?
Increasing diastolic length increases the amount of time that there is optimum myocardial blood flow, because blood flow is obstructed during systole. This increases perfusion to the ischaemic tissue.
What is an arterio-venous anastomose?
A direct connection between an artery and vein without a capillary bed connecting them.
How are arterio-venous anastomoses incolved in temperature regulation?
In the extremities in the skin, warm arterial blood flows directly to veins to dissipate heat more quickly
What are the 2 temperature factors that affect cutaneous blood flow?
Ambient (outside) temp. and Core (internal) temp.
