Specialised Circulations Flashcards
How much body weight does the heart take up?
0.5%
What does the circulation to an organ depend on?
- Perfusion pressure
2. Vascular resistance
What does vascular resistance depend on?
Intrinsic / local factors
Extrinsic factors
What are the intrinsic factors ?
- Auto regulation
2. Mechanical compression
What are the factors of auto regulation?
Myogenic, metabolic and endothelial factors
What are the extrinsic factors?
- Nervous input (sympathetic nervous system )
2. Hormones (e.g. catacholamines, Ang II)
What is auto regulation?
The ability of an organ to maintain blood flow despite changes in perfusion pressure
What is perfusion pressure?
The pressure gradient and the pressure is generated by the force of contraction of the heart
Why is a high basal flow necessary in the heart?
The heart tissues has high basal O2 consumption and a high myocardial O2 extraction
What allows the heart to extract oxygen?
High density of myocardial capillaries
How is O2 transport increased ?
Myoglobin in myocytes
How is local autoregulatory control of coronary blood flow controlled?
Metabolism and vasoactive metabolites that are produced when the heart is working hard
Increase CO2, NO,H+,K+,lactate, PGs and adenosine ——- vasodilation
Why does sympathetic activation to the heart results in coronary vasodilation and increases coronary blood flow?
Heart rate is increased therefore increase in metabolites due to increased metabolism and they cause vasodilation of vascular smooth muscle.
Vasodilation»_space;> SNS vasoconstriction
In the cardiac cycle, when does most coronary blood flow occur?
During diastole
When is the pressure of the left ventricle, higher than the pressure in the aorta ?
During systole
