Short Term Control of Blood Pressure Flashcards
What in MAP and why does it have to be regulated?
It’s the driving force pushing blood through the systemic circulation
Must be regulated as it determines the pressure gradient which pushes blood
What are general determinants of MAP?
Blood flow in and out of arteries - if flow in exceeds flow out, then volume in aa. increases and so does MAP
What are two specific determinants of MAP?
MAP = CO X TPR
Blood flow into aorta = CO
Blood flow out = influenced by TPR
What can low BP cause?
Syncope - not enough pressure to push blood around body
What can high BP cause?
Gradually damaged BV causing blindness, kidney failure etc.
Where are baroreceptors located?
In walls of carotid arteries and aorta
What type of receptors are baroreceptors?
Tonically active stretch receptors that fire AP continuously at normal BP
How is firing of AP affected with increased BP?
Increased BP stretches baroreceptor membrane and causes increased AP firing rate
How is firing of AP affected with decreased BP?
Decreased firing
What is the action of baroreceptors?
If BP changes, the frequency of AP travelling from baroreceptors to the medullary CVS control centre changes
CVCC uses sensory input to initiate appropriate response - changes in CO and TPR
What is the effect of sympathetic innervation of the heart?
Increases HR by innervating the SA node, shortening conduction time through the AV node (shorter depolarisation) and enhancing the force of myocardial contraction
What is the effect of sympathetic innervation of the smooth muscle around vessels?
Causes arteriolar constriction which increases TPR and thus MAP and venoconstriction increases venous return to the heart (Increase EDV -> preload -> SV -> increased CO increases BP)
What is the effect of sympathetic innervation of the adrenal medulla?
Stimulate secretion of adrenaline and noradrenaline
What are 3 effects of sympathetic system which increases MAP
Innervation of:
Heart
Smooth muscle
Adrenal medulla
What nerve is used to send signals from the aortic baroreceptor to the CVCC?
Vagus nerve
What nerve is used to send signals from the carotid baroreceptor to the CVCC?
Glossopharyngeal nerve
What is the effect of the parasympathetic on the heart?
Slows HR by innervating the SA node and decreasing rate of depolarisation, but has little effect on ventricular contraction
Name 5 other input to the medullary CVCC
Cardiopulmonary baroreceptors Central chemoreceptors Chemoreceptors in muscle Joint receptors Higher centres
What is the function of cardiopulmonary baroreceptors?
Located in low resistance areas (atria and lungs) and respond to changes in blood volume -> stimulates sympathetic NS
What is the function of central chemoreceptors?
Respond to [H+] directly from CO2 to control respiratory rates
What is the action of higher centres?
Feed forward effect: anticipatory effect causing BP to increase due to the hypothalamus coordinating with the sympathetic outflow signalling for body to prepare and increase HR
What are the effects of posture on blood pressure?
When in supine position, gravitational forces are distributed evenly throughout your body and circulation
When you stand, gravity causing pooling of blood in the veins and venues of the feet/legs -> decreases venous return -> low EDV -> lower SV -> lower CO -> lower BP -> baroreceptor firing decrease
What is the Valsalva manoeuvre?
Forced expiration against a closed glottis, so no air escapes and increases intrathoracic pressure
What is the effect of the V manoeuvre on MAP?
Raising intrathoracic pressure will decrease venous return
Decrease VR -> low EDV -> low SV -> low CO -> low MAP
What are the stages in the Valsalva manoeuvre?
- Increase thoracic pressure transmitted to aorta
- Increased thoracic pressure = decrease VR ->->->-> decrease MAP
- Decrease MAP detected by baroreceptors which initiate reflex increase in CO and TPR
- Stop manoeuvre and decrease in thoracic pressure
- VR restored so increase SV, but relax effect not worn off (period of high MAP)
- Back to normal
How can the Valsalva manoeuvre treat SVT?
Following the release of the breath, a parasympathetic response is triggered to decrease the heart rate. This vagal influence is what may break the SVT and lowers the heart rate
