Short Term Control of Blood Pressure

Question 1

What in MAP and why does it have to be regulated?

Answer 1

It’s the driving force pushing blood through the systemic circulation
Must be regulated as it determines the pressure gradient which pushes blood

Question 2

What are general determinants of MAP?

Answer 2

Blood flow in and out of arteries - if flow in exceeds flow out, then volume in aa. increases and so does MAP

Question 3

What are two specific determinants of MAP?

Answer 3

MAP = CO X TPR

Blood flow into aorta = CO
Blood flow out = influenced by TPR

Question 4

What can low BP cause?

Answer 4

Syncope - not enough pressure to push blood around body

Question 5

What can high BP cause?

Answer 5

Gradually damaged BV causing blindness, kidney failure etc.

Question 6

Where are baroreceptors located?

Answer 6

In walls of carotid arteries and aorta

Question 7

What type of receptors are baroreceptors?

Answer 7

Tonically active stretch receptors that fire AP continuously at normal BP

Question 8

How is firing of AP affected with increased BP?

Answer 8

Increased BP stretches baroreceptor membrane and causes increased AP firing rate

Question 9

How is firing of AP affected with decreased BP?

Answer 9

Decreased firing

Question 10

What is the action of baroreceptors?

Answer 10

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

Question 11

What is the effect of sympathetic innervation of the heart?

Answer 11

Increases HR by innervating the SA node, shortening conduction time through the AV node (shorter depolarisation) and enhancing the force of myocardial contraction

Question 12

What is the effect of sympathetic innervation of the smooth muscle around vessels?

Answer 12

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)

Question 13

What is the effect of sympathetic innervation of the adrenal medulla?

Answer 13

Stimulate secretion of adrenaline and noradrenaline

Question 14

What are 3 effects of sympathetic system which increases MAP

Answer 14

Innervation of:
Heart
Smooth muscle
Adrenal medulla

Question 15

What nerve is used to send signals from the aortic baroreceptor to the CVCC?

Answer 15

Vagus nerve

Question 16

What nerve is used to send signals from the carotid baroreceptor to the CVCC?

Answer 16

Glossopharyngeal nerve

Question 17

What is the effect of the parasympathetic on the heart?

Answer 17

Slows HR by innervating the SA node and decreasing rate of depolarisation, but has little effect on ventricular contraction

Question 18

Name 5 other input to the medullary CVCC

Answer 18

Cardiopulmonary baroreceptors 
Central chemoreceptors 
Chemoreceptors in muscle 
Joint receptors 
Higher centres

Question 19

What is the function of cardiopulmonary baroreceptors?

Answer 19

Located in low resistance areas (atria and lungs) and respond to changes in blood volume -> stimulates sympathetic NS

Question 20

What is the function of central chemoreceptors?

Answer 20

Respond to [H+] directly from CO2 to control respiratory rates

Question 21

What is the action of higher centres?

Answer 21

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

Question 22

What are the effects of posture on blood pressure?

Answer 22

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

Question 23

What is the Valsalva manoeuvre?

Answer 23

Forced expiration against a closed glottis, so no air escapes and increases intrathoracic pressure

Question 24

What is the effect of the V manoeuvre on MAP?

Answer 24

Raising intrathoracic pressure will decrease venous return

Decrease VR -> low EDV -> low SV -> low CO -> low MAP

Question 25

What are the stages in the Valsalva manoeuvre?

Answer 25

1. Increase thoracic pressure transmitted to aorta
2. Increased thoracic pressure = decrease VR ->->->-> decrease MAP
3. Decrease MAP detected by baroreceptors which initiate reflex increase in CO and TPR
4. Stop manoeuvre and decrease in thoracic pressure
5. VR restored so increase SV, but relax effect not worn off (period of high MAP)
6. Back to normal

Question 26

How can the Valsalva manoeuvre treat SVT?

Answer 26

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