short term control of blood pressure Flashcards
What happens when MAP is too low?
Syncope (Fainting)
What happens when MAP is too high?
Hypertension
Where are the baroreceptors located?
In the aortic arch and in each bifurcation of the carotid arteries
What sort of receptors are baroreceptors?
Essentially they are stretch receptors, they stretch more when MAP is larger
What happens to the baroreceptor firing rate as MAP increases?
It also increases
Below what MAP do baroreceptors not fire?
40mmHg
above what MAP does a baroreceptors firing rate stop increasing?
120mmHg
What is the centre in the brain that integrates information about BP from baroreceptors?
Medullary Cardiovascular centre
Which nerve transmits AP from the aortic arch baroreceptors to the medullary cardiovascular centre?
Vagus nerve
Which nerve transmits AP from the carotid sinus baroreceptors to the medullary cardiovascular centre?
Glossopharyngeal nerve
Which nerve carries signals from the medullary cardiovascular centre to the heart to bring about a parasympathetic response?
The vagus nerve
What is the parasympathetic response from the medullary cardiovascular centre on the heart in response to increase MAP?
Causes a decrease in heart rate
What is the sympathetic response from the medullary cardiovascular centre on the heart in response to decreased MAP?
Increased heart rate and increased contractility
What do the sympathetic fibres from the medullary cardiovascular centre do apart from increasing heart rate and contractility to increase MAP?
Cause venoconstriction and arteriolar constriction, also cause release of adrenaline from the adrenal medulla
What are the ways in which blood pressure is monitored in the short term?
Arterial baroreflex, cardiopulmonary baroreceptors, central chemoreceptors, chemoreceptors in muscle, joint receptors, higher centres
How do cardiopulmonary baroreceptors monitor blood pressure?
They are found in areas of low pressure and monitor pressure in the same way as the arterial baroreflex (via stretch receptors)
How do central chemoreceptors monitor and alter blood pressure?
They mainly affect respiratory drive but can also affect heart rate to alter BP
How do chemoreceptors in muscles work?
Receptors in the vessels of muscles detect when muscles are working harder and increase blood flow to these regions to increase washing out of waste products and delivery of nutrients
How do joint receptors work to alter MAP?
Detect increase movement of joint and increase blood flow to these regions to supply hard working muscles
How do higher centres control blood pressure?
The hypothalamus increases blood pressure in response to an increase to a stimulus that requires an increased BP, eg seeing danger
What are the main receptors for the long-term control of BP?
Cardio-pulmonary baroreceptors
How does standing up affect blood pressure?
Increased hydrostatic pressure causes pooling of blood in veins and venules of the feet and legs. This causes a decreased venous return which in turn causes a decreased EDV so preload decreases and CO decreases, this causes a decrease in MAP.
What is the reflex response to the decreases blood pressure on standing?
Decreased vagal tone which causes increased HR and CO. An increased sympathetic tone which causes an increased HR and CO, an increased contractility (increased SV and CO), venoconstriction and arteriolar constriction (which causes increased TPR)
What is the Valsava manoeuvre?
Forced expiration against a closed glottis
Describe the changes in MAP when performing the Valsava manoeuvre?
- Increases thoracic pressure is transmitted to the aorta so MAP increases
- The MAP then decreases as VR decreases (as increases pressure in thoracic veins causes loss of pressure gradient) which causes a decreased EDV therefore a decreased SV, CO and MAP.
- The decrease in MAP is detected by the arterial baroreceptors which initiate a reflex to increase CO and TPR.
- Forced expiration ceases and the decreased thoracic pressure is transmitted through to the aorta
- VR is now restored and SV increases but the reflex effects have not worn off so BP is very high
- Baroreceptors kick in again and MAP returns to normal
