CO-ORDINATED CVS RESPONSES – GRAVITY AND EXERCISE

Question 1

What happens on orthostasis(standing)?(Blood pressure)

Answer 1

Blood pressure falls at first
- Postural hypotension, lack of blood flow to the brain
o Faint

Question 2

How does the body recover from the fall in BP due to orthostasis?

Answer 2

Quickly recovers

- Due to homeostatic mechanisms such as the baroreflex

Question 3

What does the baroreflex integrate in order to recover?

Answer 3

Baroreflex integrates three smaller changes

• Heart rate increases
• Heart contractility increases
• Total peripheral resistance increases

Question 4

What is Bernoulli’s law?

Answer 4

• Blood flow = pressure energy + potential energy + kinetic energy

Question 5

What does gravity induce?

Answer 5

Gravity Induced High Venous Blood Pressures

Question 6

What is the high pressure in the venous system at the feet due to?

Answer 6

• The high pressure in the venous system at the feet is due to hydrostatic pressure

Question 7

Where is pressure higher in the tube and what does the magnitude of pressure depend on?

Answer 7

• Pressure (P) is higher at the bottom of the tube

o The magnitude of pressure depends on the height of the fluid column, the density of the fluid, and gravity

Question 8

How much venous pooling do we have in legs and what does this reduce?

Answer 8

• You have venous pooling of 500ml in legs, which reduces blood returning to the heart

Question 9

How does orthostasis cause hypotension?

Answer 9

-	Orthostasis causes a fall in CVP
o	Leads to decreased stroke volume (Starling’s Law)
o	Decreased cardiac output
o	Decreased BP
o	Poorer perfusion of the brain 
o	Dizziness and fainting

Question 10

What is the reflex response to orthostasis?

Answer 10

1) Less stimulation (unloading) of baroreceptors
2) Lower afferent fibre activity
3) Switches off inhibitory nerves that go from the CVLM to the RVLM
4) Results in RVLM being more active
a. Sends efferent signals to heart and arterioles
5) Many different effects
a. Increased sympathetic drive to SAN and increased HR
b. Myocardium has increased contractility
c. Vasoconstriction (arterioles, veins) which increases TPR
d. Less vagal parasympathetic activity to SAN
i. Overall increase in BP

Question 11

What makes postural hypotension worse?

Answer 11

• α-adrenergic blockade, generalised sympathetic blockade or other drugs that reduce vascular tone
• Varicose veins
• Lack of skeletal muscle activity
• Reduced circulating blood volume
• Increased core temperature

Question 12

What effect on CVS due to microgravity(space) is there initially?

Answer 12

o Blood is not pooling in the feet and returning to the heart easily
o Increases atria/ventricle volume and so increased preload and cardiac output
 This is sensed by cardiac mechanoreceptors leading to a reduction in sympathetic activity
o This reduces ADH and decreases atrial natriuretic peptide (ANP)
o There is increased glomerular filtration rate (GFR)
o Reduced RAAS
o An overall reduction in blood volume (BV) by 20%

Question 13

What is the long term effect of microgravity on CVS?

Answer 13

o Less BV, reduces stress on heart, heart reduces in muscle mass, general drop in BP

Question 14

What is the effect on CVS when returning to gravity from microgravity?

Answer 14

o Severe postural hypotension, due to much smaller heart and lower BV
o Baroreceptor reflex cannot compensate

Question 15

Dynamic cardiovascular responses to exercise

Answer 15

• Constantly shortening and relaxing with lots of different muscle groups involved

Question 16

Static cardiovascular response to exercise

Answer 16

• One specific muscle group is being worked without constant movement

Question 17

What type of response is there to exercise?

Answer 17

Coordinated response to exercise

Question 18

How is the coordinated response to exercise integrated?

Answer 18

• Integrated by central command in the brain

Question 19

What can just anticipation of exercise cause?

Answer 19

• Just anticipation of exercise will cause some of the changes to be initiated

Question 20

What happens once exercise commences and what are they all going to do?

Answer 20

• Once exercise commences, there is feedback from the muscles via mechanoreceptors and metaboreceptors
• They are all going to increase sympathetic activity and reduce vagus inhibition

Question 21

Main effects of exercise (lung oxygen uptake)

Answer 21

• Increase lung oxygen uptake

o Transport around the body and supply to exercising muscle

Question 22

Main effect of exercise(BP)

Answer 22

• Control BP
  o Despite huge changes in CO and resistance
   (protect heart from excessive afterload which will reduce CO)

Question 23

How is oxygen delivered during exercise?

Answer 23

• Need to selectively target areas where the oxygen is delivered so co-ordinated dilation/constriction of vascular beds

Question 24

What does integration of several adaptions create?

Answer 24

• Integration of several small adaptations create overall large response to exercise

Question 25

What can increase during strenuous exercise and by how many times?

Answer 25

- O2 uptake by pulmonary circulation can increase 10-15 times during strenuous exercise

Question 26

How is an increase in O2 uptake during exercise brought about?

Answer 26

o This very big change is brought about by the integration of three smaller changes  HR increases 3x  SV increases 1.5x  Arteriovenous O2 difference

Question 27

Max heartrate equation

Answer 27

- Maximum HR = 220 – age (approximate increase 65 to 195) 3x

Question 28

What are the increases and decreases which occur in tachycardia?

Answer 28

- Decrease in vagal tone (SA & AV nodes) | - Increase in sympathetic activity (Sa & AV nodes)

Question 29

Why is there an increase in stroke volume during exercise?

Answer 29

- Increased sympathetic activity - Increased End-Diastolic Volume o Increase in venous return/CVP through veno-constriction o Increase in sympathetic activity & calf muscle pump  Activates Starling law which increases preload - Faster ejection o Increase in contractility by sympathetic activation of β1 receptors (inotropic increase in Ca2+) - Decreased end-systolic volume o (increase in ejection fraction) o Accounts for increase in SV o Increase in contractility by sympathetic activation of β1 receptors & Starling’s law

Question 30

In leg muscles, why is there a fall in local resistance?

Answer 30

o There is a fall in local resistance due to metabolic hyperaemia vasodilation

Question 31

What type of response is a fall in resistance?

Answer 31

o It is a local sympathetic response and β2-mediated vasodilation via circulating adrenaline

Question 32

Where is there a high beta 2 receptor expression?

Answer 32

o β2 receptor expression is high in skeletal muscle and coronary artery

Question 33

When is there vasodilation of arterioles in active myocardium and skin?

Answer 33

- Vasodilation of arterioles in active myocardium & skin during moderate exercise

Question 34

What is the effect when there's an increased cardiac output?

Answer 34

- Large increase in CO - Relatively small increase in mean BP due to dilated skeletal muscle arterioles decreasing TPR - Large decrease in TPR

Question 35

what does Compensatory vasoconstriction of non-essential circulations prevent?

Answer 35

- Compensatory vasoconstriction of non-essential circulations prevents hypotension due to exercise-induced decreased TPR

Question 36

Where does compensatory vasoconstriction occur and what dose this prevent?

Answer 36

- Compensatory vasoconstrictions in inactive or unrequired tissues o E.g. kidney, GI tract, inactive muscle  Prevents BP from falling

Question 37

What does the RVLM control and what do they do?

Answer 37

o RVLM controls specific pre-ganglionic sympathetic nerves in the spinal cord which send out post-ganglionic nerves to specific tissues

Question 38

what type of exercise raises BP more?

Answer 38

Static Exercise Raises BP More Than Dynamic Exercise

Question 39

Static exercise

Answer 39

o Constant contraction of a small number of muscles o High load o E.g. Weight Lifting

Question 40

Dynamic exercise

Answer 40

o Shortening of many muscles o Low load o E.g. running

Question 41

What are metaboreceptors and where are they present and give a property of these receptors?

Answer 41

- Small diameter sensory fibres in skeletal muscle | o Chemosensitive – stimulated by K+, H+, which increase in exercising muscle

Question 42

Reflex effects by the stimulation of metaboreceptors

Answer 42

``` o Tachycardia (via increased sympathetic activity o Increased BP ```

Question 43

What type of response to exercise do metaboreceptors give?

Answer 43

"Pressor Response” to exercise

Question 44

When are metaboreceptors especially important?

Answer 44

o Especially important during isometric exercise (increased muscle load)  Static exercise raises BP more than dynamic exercise

Question 45

What are contracted muscles supplied by due to metabolism?

Answer 45

o Contracted muscle supplied by dilated resistance vessels due to metabolism