Short term control of blood pressure

Question 1

Why is short term control of blood pressure necessary ?

Answer 1

MAP is the driving force pushing blood through the circulation
MAP has to be regulated
Too high-> hypertension
Too low-> syncope

Question 2

Where are the baroreceptors ?

Answer 2

In the aortic arch and in the carotid sinus

Question 3

What is the purpose of baroreceptors ?

Answer 3

Detect stretch

Question 4

What nerve does the aortic arch travel up to the brain stem ?

Answer 4

Vagus nerve

Question 5

What nerve does fibres from the carotid sinus travel up ?

Answer 5

Glossopharyngeal nerve

Question 6

What is the effect of the medullary cardiovascular centres on the sympathetic nervous system ?

Answer 6

Via vagus nerve - increases the resting potential and decreases the rate of diastolic depolarization; under these circumstances the heart rate slows (I assume it has an influence on the sinoatrial node

Question 7

What is the effect of the medullary cardiovascular centres on the parasympathetic system ?

Answer 7

Activates noradrenaline release from the adrenal medulla
Sympathetic can innervate the sinoatrial node - increase heart rate
Sympathetic nerves also affect stroke volume via beta 1 receptors

Question 8

Which receptors are responsible for the constriction of smooth muscle via noradrenaline ?

Answer 8

Alpha 1 receptors

Question 9

What are the other inputs to the medullary cardiovascular centres ?

Answer 9

Cardiopulmonary baroreceptor:
	- Sensing central blood volume 
Central chemoreceptors:
	- Sensing arterial PCO2 and PO2
Chemoreceptors in muscle:
	- Sensing metabolite concentration
Joint receptors:
	- Sensing joint movement 
Higher centres:
	- Hypothalamus and cerebral cortex

Question 10

What is the effect of standing on the baroreceptors ?

Answer 10

Increased hydrostatic pressure causes pooling of the blood in the veins

• Reduced venous return
• Reduced end diastolic volume
• Reduced preload
• Reduced stroke volume
• Reduced cardiac output
• Reduced mean arterial pressure
• Reduced baroreceptor firing rate

Question 11

What is the result of forced expiration against a closed glottis ?

Answer 11

Increase in thoracic pressure

Question 12

What is the effect of the increased thoracic pressure on the mean arterial pressure ?

Answer 12

Reduced venous return - reduced EDV, reduced preload, reduced stroke volume and reduced mean arterial pressure

Question 13

What is the effect of reduced thoracic pressure on baroreceptors ?

Answer 13

Decrease in MAP is caused by increased thoracic pressure - decrease in MAP causes baroreceptors to initiate reflex (via sympathetic and parasympathetic nervous system) to increase CO and TPR - results in restored venous return and stroke volume