Short term control of blood pressure- Physiology Flashcards
What is the main mechanism that controls mean arterial pressure?
The arterial baroreflex
What are the names of the sensors that detect mean arterial pressure and where are they located
aortic sinuses in the aortic arch and in the carotid sinus in the carotid artery
What physical factor do the aortic and carotid sinuses measure?
The degree of stretch
Which nerve carries the nerve signals from
A) the aortic sinus
B) The carotid sinus
A) vagus nerve
B) glossopharyngeal nerve
Where do the vagus and glossopharyngeal nerves travel to in the brain?
an integrating centre in the brain (the medullary cardiovascular centres)
What does the medullary cardiovascular centre evoke in response to high mean arterial pressure?
Activates the parasympathetic vagus nerve which acts on the SA node in the heart
What does the medullary cardiovascular centre evoke in response to low mean arterial pressure?
Sympathetic signals can be sent along sympathetic nerves to act on the sinoatrial node. When sympathetic fibres are activated, the adrenal medulla is automatically activated too. This causes the systemic circulation of adrenaline which acts upon the heart.
Adrenaline released by the sympathetic fibres and the adrenal medullar will also act on the beta 1 receptors in the ventricular heart muscles to increase the amount of calcium released and increase the stroke volume.
Systemic adrenaline also causes venoconstriction and arteriolar constriction (via alpha 1 receptors in smooth muscle)
Other than the carotid and aortic sinuses, what inputs can the medullary cardiovascular centres ‘listen’ to?
- Cardiopulmonary baroreceptors in the atria and lungs which sense central blood volume
- Central chemoreceptors which sense arterial pCO2 and pO2
- Chemoreceptors in muscle that sense metabolite concentrations
- Joint receptors
- higher centres such as the hypothalamus and cerebral cortex (Conscious thought can then be translated into physiological change e.g. your heart rate begins to increase before you even start to exercise).
What is the valsalva manouvre?
forced expiration against a closed glottis (the action of breathing out hard without letting the air out)
Explain what happens during the valsalva manouvre
- Increased thoracic pressure causes increased pressure inside the heart and the aorta
- Increased thoracic pressure reduces the filling pressure from the veins (the pressure gradient which draws blood back up the venous system towards the heart is unbalanced). This in turn causes decreased venous return, decreased end diastolic pressure, decreased stroke volume, decreased cardiac output, decreased mean arterial pressure. The venous blood at this point is unable to flow freely into the heart so it is building up in the venous system.
- The fall in mean arterial pressure is then detected by the aortic and carotid baroreceptors which initiate a reflex increase in cardiac output and total peripheral resistance (note at phase 3 on the graph, blood pressure stops dropping and starts to increase again).
- The Valsalva manoeuvre is stopped and the air is released. This causes a decrease in thoracic pressure is transmitted through to the aorta – hence the drop in mean arterial pressure as seen on the diagram.
- At this point, venous return is restored, all of the blood that was building up in the venous system is now able to enter the heart so stroke volume increases due to the sudden massive increase in end diastolic volume and preload. but reflex effects have not worn off- because of the huge stroke volume (caused by the massive venous return), the baroreceptor reflexes start to reduce the heart rate in an attempt to reduce the blood pressure.
- Eventually, blood pressure and heart rate will return to normal parameters
What can the valsalva manoeuvre be used to assess?
The strength of an individual’s baroreflex
What can the valsalva manoeuvre be used to correct?
supraventricular tachycardia back to sinus rhythm
