Physiology - Regional Circulation Flashcards
How is blood flow intrinsically regulated?
- metabolic regulation
- endothelial regulation
- myotonic regulation
How is blood flow to tissues extrinsically regulated?
- neural stimulation
- hormonal
How are the innermost layers of myocardium supplied with blood?
There are specialised vessels in the ventricles which supply them
What is resting coronary blood flow?
225ml/min
What % of total cardiac output makes up coronary blood flow?
5%
What are the basal requirements for cardiac muscle Oxygen supply
8-10ml/min/100g of heart tissue
Does haemoglobin use all 4 of the oxygens when passing through cardiac muscle?
Yes, nearly all O2 is extracted from blood during one passage through the coronary arteries
What provides the driving force of blood flow through coronary arteries?
Pressure in aorta
What determines the rate of blood flow in coronary arteries?
Dilation/constriction of vessels
What is the primary controller of resistance in coronary vessels?
Metabolic regulation
What is active hyperaemia ?
When blood flow to tissues is increased due to increased metabolic activity
What will trigger active hyperaemia ?
Inadequate coronary flow, inadequate O2 content of blood, increased metabolic activity
What are the main substances thought to be involved in active hyperaemia?
Adenosine and nitric oxide (NO)
What is the believed mechanism in active hyperaemia ?
A reduction in the concentration of ATP in smooth muscle causes opening of K+ ATP channels, cause it hyperpolarisation and relaxation of coronary SM.
How does stimulation of sympathetic nerves affect coronary blood flow?
- triggers vasoconstriction by releasing NA which binds to α adrenergic receptors, triggering vasoconstriction
- SN activity also increases HR and contractility of CM. This causes myocardial cells to work harder, causing vasodilation of blood vessels and ACTIVE HYPEREMIA
What effect does adrenaline have on coronary vessels?
Binds to β adrenergic receptors causing vasodilation
Does vagal stimulation have an effect on coronary vessels?
- only has a slight dilatory effect of coronary resistance vessels
BUT
- vagal stimulation of heart slows HR, which means that myocardial cells aren’t very metabolically active, meaning blood vessels are slightly constricted
what effect does systole have on coronary blood flow? Which side (R/L) is this more apparent on
CBVs are compressed -
slows, stops, temporarily reverses blood flow
More apparent on left side
What is ischaemia ?
Restriction in blood supply to a tissue
What are the reasons that a myocardial infarction is dangerous?
- decreased cardiac output
- fibrillation of heart
- rupture of heart
- pulmonary oedema since blood pools in pulmonary circulation
What us the rate of blood flow to skeletal muscles at rest?
3ml/min/100g
What % of cardiac output goes to skeletal muscles when resting?
20%
What us the rate of blood flow to skeletal muscles during exercise?
60ml/min/100g
What % of cardiac output goes to skeletal muscles when during exercise ?
80%