Short Term Control of Blood Pressure Flashcards
What is the result of mean arterial pressure that is either too high or too low?
- Too low …….. Þ fainting (syncope)
- Too high …… Þ hypertension
Where are the baroreceptors?
In the aortic arch and in the carotid sinus
What is the purpose of baroreceptors?
Detect stretch
How does baroreceptor firing rate increase with mean arterial pressure?
Which nerve collects information from the baroreceptors?
Vagus nerve carries AP’s upwards to medullary cardiovascular centres from aortic baroreceptors
Glossopharyngeal collects from carotid sinus
Where do the action potentials from the baroreceptors eventually end up?
In the medullary cardiovascular centres
What is the effect of the medullary cardiovascular centres on the sympathetic and parasympathetic nervous system?
Parasympathetic - via vagus nerve - increases the resting potential and decreases the rate of diastolic depolarization; under these circumstances the heart rate slows (I assume it has an influence on the sinoatrial node)
Sympathetic - Activates noradrenaline release from the adrenal medulla
Sympathetic can innervate the sinoatrial node - increase heart rate
Sympathetic nerves also affect stroke volume via beta 1 receptors
Which receptors are responsible for the constricition of smooth muscle via noradrenaline
Alpha 1 receptors
Besides the stretch receptors what are the other inputs to the medullary cardiovascular centres?
- Cardiopulmonary baroreceptors (low pressure receptors)
- Central chemoreceptors
- Chemoreceptors in muscle
- Joint receptors - show frequent movement of muscles – high activity means there is a higher demand for oxygen
- Higher centres – feed forward systems- lets the body know activity is coming before it happens
What is the effect of standing on the baroreceptors?
Increased hydrostatic pressure causes pooling of the blood in the veins
- Reduced venous return
- Reduced end diastolic volume
- Reduced preload
- Reduced stroke volume
- Reduced cardiac output
- Reduced mean arterial pressure
- Reduced barroreceptor firing rate
What is the response to standing up - which causes a decrease in the mean arterial pressure
Decrease in the vagal tone - reducing parasympathetic activity affecting the sinoatrial node (reduces heart rate and cardiac output)
Increase in sympathetic tone (increase in heart rate and cardiac output)
Increase in contractility, increase in stroke volume and increase in cardiac output
Increase in venoconstriction (alpha 1 receptors), increases venous return increases end diastolic volume increase in stroke volume and increase in cardiac output
Increases arteriolar constriction increasing the total peripheral resistance
Why does venoconstriction increase venous return?
Majority of blood is in the venous system. If you constrict the venous system, you force the volume to go somewhere. It can’t go back (due to valves), thus it goes forward (ie. increasing venous return to the heart).
What is the result of forced expiration against a closed glottis?
Increase in thoracic pressure
What is the effect of the increased thoracic pressure on the mean arterial pressure?
Reduced venous return - reduced EDV, reduced preload, reduced stroke volume and reduced mean arterial pressure
What is the effect of reduced thoracic pressure on baroreceptors
Decrease in MAP is caused by increased thoracic pressure - decrease in MAP causes baroreceptors to initiate reflex (via sympathetic and parasympathetic nervous system) to increase CO and TPR - results in restored venous return and stroke volume
Why is there a small increase in blood pressure from the norm after the vasalva manouvre?
The sympathetic nervous system will be activated in this circumstance by the baroreceptors to increase stroke volume (contractility) and heart rate – this takes time to wear off after the thoracic pressure is restored – hence a small increase in blood pressure after the valsalva manouvre.
