Reflex control of the CVS

Question 1

What are excitatory inputs?

Answer 1

Arterial chemoreceptors, muscle metaboreceptors, Stimulation of reflexes- these increase cardiac output, TPR and blood pressure response

Question 2

What are inhibitory inputs?

Answer 2

Arterial baroreceptors, cardiac-pulmonary receptor. Stimulation of reflexes- decrease cardiac output, TPR and blood pressure

Question 3

Describe arterial baroreceptors? (7pts)

Answer 3

1. Baroreceptors are vital to maintain blood flow to the brain and the myocardium
2. Baroreceptors are pressure detecting receptors and they detect stretch.
3. There are no blood flow receptors. The body monitors blood pressure in carotid and coronary arteries
4. Monitering blood pressure:

Blood flow= Pa/ total peripheral resistance

5. A decrease in blood pressure reflects a decrease in carbon dioxide or total peripheral resistance which compromises blood flow to the brain and the heart.
6. Blood pressure sensors in the walls of the carotid arteries and aorta informs the brain of pressure changes in these key feeder vessels
7. The baroreceptors will detect arterial wall stretch.

Question 4

How do baroreceptors respond to an increase in pressure?

Answer 4

There is not much firing at rest then as pressure increases there is fast firing which eventually slows down and becomes constant but at a higher level than before. It is an adaption to a new normal

Question 5

How do baroreceptors respond to a decrease in pressure?

Answer 5

For a decrease in pressure the firing slows down proportionally

Question 6

What happens in the face of continued high or continued low pressure?

Answer 6

In the face of continued high or continued low pressure the treshhold for baroreceptor activation can change.

Question 7

What happens in long term hypertension?

Answer 7

In long term hypertension baroreceptors become normalises at the new pressure and it is less activated.

Question 8

Define loading?

Answer 8

Increase in blood pressure. It occurs during stress or exercise.

Question 9

Describe the effect of increased blood pressure on the baroreflex?

Answer 9

1. There is electrical stimulation of the carotid sinus nerve
2. Pulse pressure falls which means there is a decreased stroke volume
3. Vasodilation will decrease total peripheral resistance and blood pressure
4. This will decrease sympathetic nerve activity
5. There is increased vagus nerve activity

Question 10

Define unloading?

Answer 10

• Decrease in blood pressure

- It occurs during bleeding or haemorrhage

Question 11

Describe Unloading?

Answer 11

1. Decrease in blood pressure
2. Increased sympathetic activity and decreased vagus nerve activity occurs
3. This increased heart rate and increases the force of contraction. This will cause an increased cardiac output
4. Arterial constriction will give increased total peripheral resistance
5. Venous constriction will increase central venous pressure and so by starlings law this will increase stroke volume and cardiac output
6. This all maintains blood pressure therefore blood will flow to vital organs

• adrenaline secretion, Vasopressin ( ADH) secretion and stimulation of RAAS occurs. Angiotensin II increases Na+/ H20 reabsorption in kidneys which raises blood volume
• Vasoconstriction decreases capillary pressure which increases absorption of interstitial fluid which increases blood volume

Question 12

What are veno-atiral mechanoreceptors? (3pts)

Answer 12

1. Found on the veins in the heart
2. They are stimulated by an increase in cardiac filling
3. When the receptors are stretched they increase diuresis by switching off ADH and RAAS. This will reduce sympathetic activity to the kidneys which will increase glomerular filtration. This secretes atrial natriuretic peptide which increases sodium production.

Question 13

What are ventricular mechanoreceptors? (3pts)

Answer 13

1. These are stimulated by over distention of the ventricles. It is a depressor response
2. This is a weak reflex which causes mild vasodilatation, lower blood pressure and preload
3. Modulated by vagus afferents

Question 14

What are nociceptive sympathetic afferents? (6pts)

Answer 14

1. Signal pain
2. Stimulated by K+, H+ (lactate) and bradkin during ischaemia
3. Go to the spinal cord and the brain
4. Converge onto neurones onto the same neurones in the spinal cord as somatic afferents which cause referred pain.
5. They signal cardiac paijn e.g angina and heart attacks. This causes increased sympathetic activity- pale sweating, tachycardia.
6. The nociceptive sympathetic afferents mediate the pains of angina and myocardial infraction.

Question 15

Describe arterial chemoreceptors?

Answer 15

1. They are located in the carotid and aortic bodies
2. These are stimulated by low oxygen ( hypoxia), high carbon dioxode ( hypercapnia), H+ and K+
3. Arterial chemoreceptors regulate ventilation and drive cardiac reflexes during asphysia (which is when there is low oxygen and high levels of carbon dioxide), shock ( systematic hypotension and haemorrhage
4. Arterial chemoreceptors send signals to the medulla. From the medulla there are sympathetic nerves that act on the heart and blood vessels

Question 16

Describe the pressure response?

Answer 16

1. Asphxia occurs
2. This increases sympathetic activity
3. Tachycardia occurs which increases selective arteriall and venous constriction
4. This increases cardiac output and blood pressure especially in preservation of cerebral blood flow.

Question 17

Describe sensory fibres in Group IV motor fibres located in the skeletal muscle?

Answer 17

These are activated via metabolites K+, lactate and adenosine

Question 18

Describe pressure receptors

Answer 18

1. This increases sympathetic activity
2. This increases tachycardia and increases arterial/ nervous constriction
3. This increases cardiac output and blood pressure

Question 19

Why are muscle metaboreceptors important during isometric exercise?

Answer 19

1. Continually contracted muscle but joint angle and muscle length do not change
2. Higher blood pressures drives blood into the contracted muscle to maintain perfusion
3. These muscles undergo metabolic hyperaemia allowing blood flow to the contracted tissue

Question 20

Describe the role of the NTS?

Answer 20

• the NTS located in the medulla

1. The signal from the stretched baroreceptors is sent via afferent fibres which enter the NTS
2. This then sends information out to the CVLM
3. The CVLM sends an inhibitor signal to the RVLM
4. This results in the inhibition of sympathetic efferent nerves to the heart and vessels
5. There is less sympathetic efferent signals which results in a reduction in heart rate, less vasoconstriction and lower blood pressure

Question 21

What does loading of the baroreceptors do? (3pts)

Answer 21

1. Loading of the baroreceptors stimulates the vagus nerve which activates the NTS.
2. The signal from the NTS stimulates the nucelus ambiguous ( vagal nuceli)
3. Vagal parasymapthetic impulses are sent to the heart and these have a depressor effect.

Question 22

What occurs during the sinus Tachycardia?

Answer 22

1. Inhibitory input from the inspiratory centre occurs
2. Each inhalation will switch off the nucleus ambiguous
3. The inhibitory parasympathetic signal to the vagus nerve will decrease and heart rate will increase slightly

• heart rate is quicker when you inhale compared to exhaling

Question 23

What is the limbic system?

Answer 23

1. Emotional centre
2. Having an emotional reaction stimulates the NTS which in turn stimulates the nucleus ambiguous causing increased activity of the vagal nerve and depressor effect on the AV and SA nodes.

Question 24

What are the side effects of the limbic system?

Answer 24

1. Can lead to fainting ( syncope). This is a vasovagal attack
2. The synocope is caused by decreased blood flow due to the sudden drop in aretrail cardiac output and blood pressure

Question 25

What are the side effects of the limbic system?

Answer 25

1. Can lead to fainting ( syncope). This is a vasovagal attack
2. The synocope is caused by decreased blood flow due to the sudden drop in aretrail cardiac output and blood pressure