The Role of Exercise and Stress in Health and Disease

Question 1

List 4 primary physiological responses to mental stress.

How does autonomic activity change to bring about these effects?

Answer 1

1 - Increase in respiration.

2 - Increase in sympathetic activity and decrease in parasympathetic activity to the heart via the nucleus ambiguus and rostral ventrolateral medulla.

3 - Increased sympathetic activity to vessels supplying the kidney, GIT and skin via the rostral ventrolateral medulla, causing vasoconstriction.

4 - Decreased sympathetic activity (alpha 1) and an increase in circulating adrenaline (beta 2) to skeletal muscle, causing vasodilation.

Question 2

List 5 secondary physiological responses to mental stress.

Answer 2

1 - Pupillary dilation.

2 - Sweating.

3 - Piloerection.

4 - Urination.

5 - Defecation.

Question 3

Define habituation and sensitisation.

Answer 3

• Habituation is the dampening of a response to a stressor with repeated exposure.
• Sensitisation is the amplification of a response to a stressor with repeated exposure.

Question 4

Define conditioning.

Answer 4

The increase in frequency of a particular response to a stimulus as a result of reinforcement.

Question 5

Describe the organisation of the defence areas in the brain.

Answer 5

• Afferents synapse at these sites:

• Amygdala (one in each of the temporal lobes), which leads to the ventral hypothalamus.
• The ventral hypothalamus, which leads to the midbrain periaqueductal grey area.
• The midbrain periaqueductal grey area, which leads to the dorsal medulla.

• Efferents originate from these sites:

• The dorsal medulla leading to the ventral medulla, from which efferent outflow via the RVLM, respiratory neurones and the nucleus ambiguus propagates.

• Other components:

• A loop exists between the ventral hypothalamus and the amygdala, allowing for continuous stimulation of the system.
• The prefrontal cortex (in the frontal lobe) modulates this system by exciting or inhibiting the amygdala.

Question 6

What is the effect of mental stress on the baroreceptor reflex?

What is the consequence of this on arterial blood pressure?

Answer 6

• The baroreceptor reflex is suppressed.

- Arterial blood pressure can become very high.

Question 7

Which defence area of the brain is responsible for the modulation of the baroreceptor reflex?

Answer 7

The midbrain periaqueductal grey area.

Question 8

Give an example of a condition that might occur in individuals who do not habituate easily to repeated emotional stress.

Answer 8

Essential (primary) hypertension.

Question 9

Describe the pathophysiology of essential hypertension.

Answer 9

• Arterial blood pressure increases as a result of environmental stressors acting via the defence areas of the brain.
• This causes hypertrophy of vascular smooth muscle in arterioles.
• This increases TPR and therefore arterial blood pressure.

Question 10

What is vasovagal syncope?

When does it occur?

Answer 10

• Emotional fainting due to a sudden increase in vagal activity to the heart and a decrease in sympathetic activity to blood vessels (directing blood away from the brain and towards the periphery).
• Typically preceded by an alerting response due to emotional stress.
• Sometimes occurs after strenuous exercise or major haemorrhage.

Question 11

Describe the mechanisms that underlie vasovagal syncope / the vasovagal reflex response.

Answer 11

1 - A strong alerting response leads to an increase in heart rate and ventricular contractility.

2 - When this increase becomes excessively high, although the ventricles are contracting very strongly, ventricular filling (EDV) decreases, particularly when standing (due to venous pooling). This decreases arterial blood pressure

3 - In addition to the fall in EDV, the torsion of the ventricles stimulates ventricular mechanoreceptors with vagal afferents.

4 - The afferent vagal activity leads to the nucleus tractus solitarius in the medulla, and then to the lateral hypothalamus.

5 - This evokes a reflex to increase vagal efferent activity to the heart and decrease sympathetic activity to blood vessels.

6 - This profoundly decreases blood pressure, causing the patient to faint when blood flow to the brain falls.

Question 12

What response attempts to antagonise the loss of blood volume due to haemorrhage?

Answer 12

The baroreflex, which increases sympathetic activity to the ventricles.

Question 13

List 4 influences of exercise on cardiovascular and respiratory activity.

Answer 13

1 - Volition (cortical influences), such as increasing respiration.

2 - Local vasodilation in muscles.

3 - Mechanical influences of contraction

4 - The exercise reflex (explained in a later card).

Question 14

List 3 mediators of local vasodilation in muscle.

Answer 14

1 - K+.

2 - Pi.

3 - Adenosine.

Question 15

Other than sympathetic activity, what counteracts the action of local vasodilators in muscle?

Answer 15

The mechanical influences of contraction.

Question 16

Why does TPR tend to increase during static contraction but decrease during rhythmic contraction?

Answer 16

• The effects of the mechanical influences of contraction are greater than that of local vasodilation during static exercise, so the balance leans towards an increase in TPR.
• The effect of local vasodilation is greater than the that of the mechanical influences of contraction during rhythmic exercise, so the balance leans towards a decrease in TPR.

Question 17

Which receptors are stimulated by metabolites of muscle contraction?

Answer 17

Metaboreceptors.

Question 18

Which receptors are stimulated during dynamic exercise but are not stimulated during static exercise?

Answer 18

Joint receptors.

Question 19

Describe the exercise reflex.

Answer 19

1 - Stimulation of metaboreceptors and joint receptors during exercise produces afferent activity to the subthalamic locomotor region (SLR), AKA the exercise integrating area.

This evokes a reflex that:

2 - Increases respiration by increasing motor activity to the diaphragm and intercostal muscles via central respiratory neurones.

3 - Increases heart rate and contractility by increasing sympathetic activity and decreasing parasympathetic activity to the heart via cardiac vagal motor neurones originating at the nucleus ambiguus.

4 - Increases sympathetic noradrenergic activity to the GIT, kidney, skin and skeletal muscles via the rostral ventrolateral medulla, causing vasoconstriction.

Question 20

How can the exercise reflex be modulated by external influences?

Answer 20

Central command can increase the exercise reflex by exciting the subthalamic locomotor region directly.

Question 21

What is the overall effect of the exercise reflex and functional hyperaemia on skeletal muscle blood flow?

What is this known as?

What might complicate this balance?

Answer 21

• Functional hyperaemia overcomes the vasoconstriction caused by the exercise reflex.
• This is known as functional sympatholysis.
• This might be complicated by the mechanical influences of contraction.

Question 22

What is the overall effect of exercise on TPR (considering both the exercise reflex and functional hyperaemia) during:

dynamic exercise?

static exercise?

Answer 22

• During dynamic exercise, TPR changes very little, because although systolic pressure increases, diastolic pressure decreases due to the vasodilation in muscle.
• During static exercise, TPR is more likely to increase because systolic pressure increases, and diastolic pressure also increases due to the greater effects of the mechanical influences of contraction, which increases TPR.

Question 23

How does the baroreceptor reflex respond to changes in arterial blood pressure due to exercise?

Answer 23

• The baroreceptor reflex buffers rises in arterial blood pressure.
• However the set point for arterial blood pressure is increased, reducing its effects.

Question 24

How does the cerebral circulation respond to changes in arterial blood pressure due to exercise?

Answer 24

It will autoregulate to maintain a constant blood pressure.

Question 25

What is the anaerobic threshold?

Answer 25

• The point at which chemoreceptors start to be stimulated due to an increase in demand for oxygen.
• The point at which respiring tissues begin to respire anaerobically due to a lack of supply of oxygen.

Question 26

Below the anaerobic threshold, what maintains blood concentrations of oxygen and carbon dioxide?

Answer 26

Changes in ventilation due to the exercise reflex.

Question 27

What is the primary local vasodilator in the coronary circulation?

Answer 27

Adenosine.

Question 28

Why is greater coronary vasodilation required in static exercise?

For whom might this be a problem?

Answer 28

• Because static exercise necessitates a greater increase in cardiac work as in static exercise, the skeletal muscle pump only increases EDV at the onset of contraction, whereas the skeletal muscle pump helps to rhythmically maintain EDV in dynamic exercise.
• Also, static exercise increases TPR, whereas dynamic exercise only changes TPR by small amounts.
• This might be a problem for patients with coronary artery disease.