Short Term Control of Blood Pressure

Question 1

What is MAP?

Answer 1

Is the driving force pushing blood through the circulation

Question 2

What happens if MAP is too high?

Answer 2

Hypertension if for a long period of time - lead to stroke
No immediate effects

Question 3

What happens if MAP is too low?

Answer 3

Can cause fainting - syncope
If fainted then gravity is not causing blood to pool in veins so EDV is restored with preload so regain consciousness

Question 4

What is MAP equal to?

Answer 4

MAP = CO x TPR

Question 5

Explain the arterial baroreflex

Answer 5

Detect changes in pressure in indirect way
Aortic arch and carotid sinus baroreceptors are stretch receptors. On internal carotid arteries

Question 6

What does increase or decrease in pressure mean for firing rate?

Answer 6

Increase in pressure - increased firing rate
Decrease in pressure - decreased firing rate

Question 7

What nerve carries signal to medullary cardiovascular centres for carotid sinus baroreceptor?

Answer 7

Glossopharyngeal nerve

Question 8

What nerve carries signal to medullary cardiovascular centre from aortic arch baroreceptor?

Answer 8

Vagus nerve

Question 9

What happens when signal are transmitted from medullary cardiovascular centre along parasympathetic nerve?

Answer 9

Release of ACh
Causes decrease in HR as hyperpolarises cells which means take longer to produce AP
No change in muscle activity

Question 10

What happens when signal from medullary cardiovascular centre is transmitted along sympathetic nerve?

Answer 10

Release of Noradrenaline which increase HR and contractibility as increase in release of Ca2+
Adrenaline and NA released at adrenal medulla to cause venoconstriction and arteriolar constriction

Question 11

What does cardiopulmonary baroreceptors sense?

Answer 11

Central blood volume
Found in atria and walls of vessels in lungs - stretch receptors

Question 12

What does central chemoreceptors sense?

Answer 12

Arterial pCO2 and pO2
Increase in pCO2 and decrease in pO2 cause stimulation of resp. drive

Question 13

What does chemoreceptors in muscles sense?

Answer 13

Sensing metabolite concentrations ex. exercise or if more blood is needed

Question 14

What do joint receptors sense?

Answer 14

Joint movement - send signals if need more blood

Question 15

What are some higher centres that input to medullary cardiovascular centres?

Answer 15

Hypothalamus - thermoregulation
Cerebral cortex - strong emotional stimulus

Question 16

What is the Valsalva manoeurve?

Answer 16

Forced expiration against a closed glottis
Mouth is closed
Increases thoracic pressure so has effect on CVS

Question 17

What is phase I of Valsalva manoeuvre on blood pressure?

Answer 17

Increased thoracic pressure transmitted through to the aorta - hence immediate jump

Question 18

What is phase II of Valsalva manoeuvre on blood pressure?

Answer 18

Increased thoracic pressure reduces filling pressure from the veins which decreases VR, EDV, SV, CO and MAP
Because blood is pushed away from expiration

Question 19

What is the last II phase of Valsalva manoeuvre?

Answer 19

Reduced MAP is detected by baroreceptors which initiate reflex increase in CO and TPR
Because there is increase sympathetic tone so release of NA which increase HR

Question 20

What is phase III of Valsalva manoeuvre on blood pressure?

Answer 20

AT the end of the manoeuvre there is a decrease in thoracic pressure which is transmitted through to aorta
Hence drop in BP

Question 21

What is phase IV of Valsalva manoeuvre on blood pressure?

Answer 21

Venous Return is returned so increase in SV but the reflex effects have not worn off
Increase in vagal tone so decrease in HR which decreases CO and BP can be restored

Question 22

What is the clinical significance of the Valsalva manoeuvre?

Answer 22

Used as a test of autonomic function which can be reduced in older people or if people have autonomic neuropathy

Question 23

What happens if BP continues to fall and does not resolve?

Answer 23

Can increase risk of myocardial infarction - heat under strain
Supraventricular tachycardia