Reflex Control Of The Circulation

Question 1

Give examples of excitatory inputs

Answer 1

Arterial chemoreceptors, muscle metaboreceptors

Question 2

Give examples of inhibitory inputs

Answer 2

Arterial baroreceptors, cardiac-pulmonary receptors

Question 3

What are arterial baroreceptors important for?

Answer 3

Vital to maintain blood flow to brain and myocardium

Question 4

Where does the body monitor blood pressure?

Answer 4

Carotid and coronary arteries

Question 5

How does blood pressure monitoring tell us about blood flow?

Answer 5

Pa = CO x TPR

Question 6

What does a decrease in Pa reflect?

Answer 6

Either a decrease in CO or TPR which compromises blood flow to the brain or heart

Question 7

Where are the blood pressure sensors found?

Answer 7

In the walls of the carotid arteries/ aorta

Question 8

What happens with the baroreceptors when there’s an increase in pressure?

Answer 8

As pressure increases, fast firing which eventually slows down and becomes constant, but at a higher level than before

Question 9

What happens to the baroreceptors when there’s a decrease in pressure?

Answer 9

The firing slows down proportionately

Question 10

What happens when there’s continued low or high pressure in the baroreceptors?

Answer 10

The threshold changes

Question 11

What is the effect of an increased blood pressure on the heart (5)?

Answer 11

Increase in BP = loading

• pulse pressure falls
• vasodilation decreases TPR and BP
• decreased sympathetic nerve activity
• increased vagal nerve activity

Question 12

What is the effect of decreased blood pressure on baroreflex?

Answer 12

Decrease in BP = unloading

• increased sympathetic activity and decreased vagal activity
• increased heart rate and force of contraction so cardiac output is increased
• arterioles constriction gives increased TPR
• venous constriction increases central venous pressure and increases stroke volume and cardiac output

Question 13

What are veno-atrial mechanoreceptors stimulated by?

Answer 13

Increase in cardiac filling/ cardiac venous pressure

Question 14

How do veno-atrial mechanoreceptors work?

Answer 14

Increased diuresis switches off ADH and RAAS-> less sympathetic activity to kidneys, so more glomerular filtration. This then secretes atrial natriuretic peptide

Question 15

What nerve is connected to the veno-atrial mechanoreceptors?

Answer 15

Vagus afferents

Question 16

What are ventricular mechanoreceptors stimulated by?

Answer 16

Over distension of vesicles

Question 17

What happens when the ventricular mechanoreceptors are stimulated?

Answer 17

Weak reflex- mild vasodilation, lower blood pressure and preload

Question 18

What are the nociceptive sympathetic afferents stimulated by?

Answer 18

K+, H+ and bradykinin during ischaemia

Question 19

What do the nociceptive sympathetic afferents do?

Answer 19

Mediate pain of angina and myocardial infarction. Reflex increased sympathetic activity

Question 20

What happens when afferent fibres from the baroreceptors are removed?

Answer 20

Arterial pressure varies enormously, but the mean isn’t that different

Question 21

What happens when afferent fibres from cardiac receptors and baroreceptors are removed?

Answer 21

Arterial pressure varies and the mean is very different

Question 22

What happens if the arterial pressure drops to 50mmHg?

Answer 22

Cause insufficient perfusion to end organs

Question 23

What happens if the arterial pressure rises to 150mmHg?

Answer 23

Damage the cardiovascular system

Question 24

Where are arterial chemoreceptors located?

Answer 24

Carotid and aortic bodies

Question 25

What are arterial chemoreceptors stimulated by?

Answer 25

Low O2, high CO2, H+ and K+

Question 26

What do arterial chemoreceptors regulate?

Answer 26

Ventilation and also drive cardiac reflexes during asphyxia, shock and haemorrhage

Question 27

What are the arterial chemoreceptors responses?

Answer 27

Increased sympathetic activity, tachycardia and increased cardiac output and blood pressure

Question 28

What are muscle metaboreceptors and where are they found?

Answer 28

Sensory fibres in group IV motor fibres located in skeletal muscle

Question 29

How are muscle metaboreceptors activated?

Answer 29

Via metabolites like K+, lactate and adenosine

Question 30

What do the muscle metaboreceptors cause?

Answer 30

Increase in sympathetic activity Tachycardia -> more arterial/venous constriction Increase cardiac output blood pressure

Question 31

When are muscle metaboreceptors really important?

Answer 31

During isometric exercise

Question 32

What happens during isometric (static) exercise?

Answer 32

Bigger blood pressure drives blood into the contracted muscle to maintain perfusion. These then undergo metabolic hyperaemia, which allows blood to flow to the contracted muscle

Question 33

What is the central role of the nucleus tractus solitarius?

Answer 33

Signal from stretched baroreceptor is sent via afferent fibres and enters the NTS NTS signals to CVLM CVLM signals to RVLM Sympathetic efferent nerves to heart and vessels are inhibited so lower heart rate vasoconstriction and stuff

Question 34

What does CVLM stand for?

Answer 34

Caudal ventrolateral medulla

Question 35

What does RVLM stand for?

Answer 35

Rostral ventrolateral medulla

Question 36

How is the nucleus ambiguous stimulated and what is its effect?

Answer 36

Stimulated by the NTS Causes vagal parasympathetic impulses to be sent to the heart where they have a depressor effect

Question 37

What is sinus tachycardia?

Answer 37

An inhibitory input from the inspiration centre. Each inhalation switches off nucleus ambiguous. This increases the inhibitory parasympathetic signal to the vagus

Question 38

What is the vaso vagal syncope?

Answer 38

Vagal parasympathetic outflow

Question 39

How does the vasovagal syncope work?

Answer 39

The lymbic system stimulates NTS which stimulates the nucleus ambiguous which causes an increase in the activity of the vagal nerve and depressor effect on the AV and SA nodes

Question 40

How do you have a vasovagal attack?

Answer 40

Fainting is caused by decreased cerebral blood flow due to a sudden drop in the arterial cardiac output and blood pressure