46 Questions
What happens to diastole when heart rate is increased?
It becomes shorter
What is the primary mechanism by which coronary blood flow increases during exercise?
Accumulated metabolites causing vasodilation
What is the percentage of cardiac output that is allocated to the coronary circulation at rest?
4%
What happens to coronary blood flow during systole?
It becomes zero
What is the effect of ischaemia on coronary collaterals?
It promotes their formation
What is the effect of increased heart rate on diastolic pressure?
It decreases
What is the relationship between diastole and coronary blood flow?
Coronary blood flow is highest during diastole
What happens to coronary arteriolar tone during exercise?
It decreases
What is the effect of sympathetic stimulation on coronary arterioles?
It causes vasoconstriction
What is the relationship between cardiac output and coronary blood flow during exercise?
Coronary blood flow increases when cardiac output increases
What is the primary effect of sympathetic nerves on blood vessels?
Vasoconstriction in splanchnic, renal, and cutaneous vascular beds
Which of the following hormones acts to decrease total peripheral resistance in response to increased blood volume?
Atrial natriuretic peptide (ANP)
Which type of receptor is primarily involved in the parasympathetic regulation of blood flow?
Muscarinic receptors
What is the primary effect of oxidative stress on blood vessels?
Impaired ability to dilate
Under normal conditions, which neurotransmitter is more important in mediating the effects of the sympathetic nervous system on the cardiovascular system?
Noradrenaline
What is the characteristic of coronary flow reserve?
Very large
Which of the following organs is primarily regulated by the parasympathetic nervous system in terms of blood flow?
Salivary glands and pancreas
What is the primary effect of angiotensin II on the cardiovascular system?
Vasoconstriction and increased total peripheral resistance
Why does right ventricular blood flow continue throughout the cardiac cycle?
Because RV pressure is lower than LV pressure
Which of the following is NOT a target of sympathetic nervous system-mediated vasoconstriction?
Salivary glands
What happens to diastolic pressure during systole?
It increases
What is the effect of stenosis on coronary blood flow?
It decreases blood flow
What is the compensatory mechanism for stenosis in coronary blood flow?
Vasodilatory autoregulation
At what percentage of stenosis does vasodilatory autoregulation fail?
90%
What is the effect of chronic stenosis on the microvasculature?
It impairs endothelial function
What is the result of prolonged ischaemia in coronary arteries?
Development of intra-arterial collaterals
What is the relationship between DP and flow through the microvasculature?
Large DP – strong flow
What is the effect of stenosis on DP?
It decreases DP
What is the primary reason for the constant cerebral blood flow requirement?
Because the brain's metabolic demand remains relatively constant despite physical activity
What is the equation that describes cerebral blood flow?
Flow = P/R
What is the result of a decrease in perfusion pressure in the cerebral arterioles?
Vasoconstriction and decreased blood flow
What is the primary mechanism that helps to regulate cerebral blood flow during changes in cardiac output and/or MAP?
Negative feedback mechanism
What is the result of increased CO2 in the cerebral arterioles?
Vasodilation and increased blood flow
What is the purpose of flow auto-regulation in the cerebral circulation?
To maintain constant blood flow despite changes in cardiac output and/or MAP
What is the result of increased perfusion pressure in the cerebral arterioles?
Vasoconstriction and decreased blood flow
What is the myogenic mechanism responsible for in the cerebral circulation?
Responding to changes in perfusion pressure
What is the consequence of too much blood flow to the cerebral vessels?
Cerebral haemorrhage
What is the purpose of the negative feedback mechanism in the cerebral circulation?
To bring blood flow back to normal after a change in perfusion pressure
What is the primary function of vascular tone in the body?
To regulate blood pressure and regional vascular resistances
Which of the following factors does NOT contribute to vascular tone?
Age
What is the primary mechanism by which the vascular endothelium regulates vascular tone?
Release of NO and EDH
What is the result of endothelial dysfunction on vascular tone?
Increased vascular tone
What mechanism allows arteries to maintain a constant blood flow over a wide range of pressures?
Flow autoregulation
What allows tissues to regulate their own blood supply?
Metabolic hyperaemia
When does coronary blood flow to the left ventricle occur mainly?
During diastole
What is the result of increased cardiac work on coronary blood flow?
Increased coronary blood flow
Study Notes
Autonomic Nervous System (ANS) and Blood Flow Regulation
- Sympathetic nerves cause vasoconstriction, especially in splanchnic, renal, cutaneous, and muscle vascular beds, mainly via noradrenaline and α1 receptors.
- Parasympathetic nerves cause vasodilatation in specific organs, such as salivary glands, pancreas, intestinal mucosa, and penis, mainly via acetylcholine and muscarinic receptors.
Circulating Hormones and Blood Pressure Regulation
- Anti-diuretic hormone (vasopressin) from the posterior pituitary raises total peripheral resistance (TPR) in response to reduced blood volume.
- Angiotensin II raises TPR in response to reduced blood volume, while atrial natriuretic peptide (ANP) lowers TPR in response to increased blood volume.
Special Requirements of the Cerebral Circulation
- Cerebral blood flow must remain relatively constant, despite changes elsewhere in the body, to maintain constant brain metabolic demand.
- Flow auto-regulation ensures that cerebral blood flow is tightly controlled, responding to changes in perfusion pressure and CO2 levels.
Mechanism of Cerebral Flow Autoregulation
- Cerebral arterioles respond to changes in perfusion pressure and CO2 levels, constricting or dilating to maintain constant blood flow.
- Negative feedback mechanisms, such as increased CO2 washout, help regulate cerebral blood flow.
Coronary Blood Flow Regulation
- Coronary blood flow varies during the cardiac cycle, peaking during diastole and falling to zero during systole.
- Increased metabolic demand and oxygen consumption in cardiac muscle lead to vasodilation and increased coronary blood flow.
- Active hyperaemia in cardiac muscle is mediated by sympathetic nervous system activation, adenosine, and increased metabolite production.
Compensatory Mechanisms in Coronary Blood Flow
- Coronary collaterals form in response to ischaemia, promoting blood flow to the affected area.
- Vasodilatory autoregulation compensates for increased resistance caused by stenosis, but only up to a point.
- Prolonged ischaemia leads to the development of intra-arterial collaterals between coronary arteries.
Learn about the role of the autonomic nervous system in regulating blood flow, including the effects of sympathetic and parasympathetic nerves on vasoconstriction and vasodilation. Also, explore the role of circulating hormones in blood pressure regulation.
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