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CVS > CO-ORDINATED CVS RESPONSES – GRAVITY AND EXERCISE > Flashcards

CO-ORDINATED CVS RESPONSES – GRAVITY AND EXERCISE Flashcards

1
Q

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

A

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

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2
Q

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

A

Quickly recovers

- Due to homeostatic mechanisms such as the baroreflex

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3
Q

What does the baroreflex integrate in order to recover?

A

Baroreflex integrates three smaller changes

  • Heart rate increases
  • Heart contractility increases
  • Total peripheral resistance increases
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4
Q

What is Bernoulli’s law?

A
  • Blood flow = pressure energy + potential energy + kinetic energy
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5
Q

What does gravity induce?

A

Gravity Induced High Venous Blood Pressures

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6
Q

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

A
  • The high pressure in the venous system at the feet is due to hydrostatic pressure
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7
Q

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

A
  • 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

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8
Q

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

A
  • You have venous pooling of 500ml in legs, which reduces blood returning to the heart
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9
Q

How does orthostasis cause hypotension?

A 
-	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
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10
Q

What is the reflex response to orthostasis?

A

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

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11
Q

What makes postural hypotension worse?

A
  • 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
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12
Q

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

A

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%

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13
Q

What is the long term effect of microgravity on CVS?

A

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

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14
Q

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

A

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

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15
Q

Dynamic cardiovascular responses to exercise

A
  • Constantly shortening and relaxing with lots of different muscle groups involved
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16
Q

Static cardiovascular response to exercise

A
  • One specific muscle group is being worked without constant movement
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17
Q

What type of response is there to exercise?

A

Coordinated response to exercise

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18
Q

How is the coordinated response to exercise integrated?

A
  • Integrated by central command in the brain
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19
Q

What can just anticipation of exercise cause?

A
  • Just anticipation of exercise will cause some of the changes to be initiated
20
Q

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

A
  • 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
21
Q

Main effects of exercise (lung oxygen uptake)

A
  • Increase lung oxygen uptake

o Transport around the body and supply to exercising muscle

22
Q

Main effect of exercise(BP)

A
  • Control BP
    o Despite huge changes in CO and resistance
     (protect heart from excessive afterload which will reduce CO)
23
Q

How is oxygen delivered during exercise?

A
  • Need to selectively target areas where the oxygen is delivered so co-ordinated dilation/constriction of vascular beds
24
Q

What does integration of several adaptions create?

A
  • Integration of several small adaptations create overall large response to exercise
25
Q

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

A
  • O2 uptake by pulmonary circulation can increase 10-15 times during strenuous exercise
26
Q

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

A

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

27
Q

Max heartrate equation

A
  • Maximum HR = 220 – age (approximate increase 65 to 195) 3x
28
Q

What are the increases and decreases which occur in tachycardia?

A
  • Decrease in vagal tone (SA & AV nodes)

- Increase in sympathetic activity (Sa & AV nodes)

29
Q

Why is there an increase in stroke volume during exercise?

A
  • 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
30
Q

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

A

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

31
Q

What type of response is a fall in resistance?

A

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

32
Q

Where is there a high beta 2 receptor expression?

A

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

33
Q

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

A
  • Vasodilation of arterioles in active myocardium & skin during moderate exercise
34
Q

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

A
  • Large increase in CO
  • Relatively small increase in mean BP due to dilated skeletal muscle arterioles decreasing TPR
  • Large decrease in TPR
35
Q

what does Compensatory vasoconstriction of non-essential circulations prevent?

A
  • Compensatory vasoconstriction of non-essential circulations prevents hypotension due to exercise-induced decreased TPR
36
Q

Where does compensatory vasoconstriction occur and what dose this prevent?

A
  • Compensatory vasoconstrictions in inactive or unrequired tissues
    o E.g. kidney, GI tract, inactive muscle
     Prevents BP from falling
37
Q

What does the RVLM control and what do they do?

A

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

38
Q

what type of exercise raises BP more?

A

Static Exercise Raises BP More Than Dynamic Exercise

39
Q

Static exercise

A

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

40
Q

Dynamic exercise

A

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

41
Q

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

A
  • Small diameter sensory fibres in skeletal muscle

o Chemosensitive – stimulated by K+, H+, which increase in exercising muscle

42
Q

Reflex effects by the stimulation of metaboreceptors

A 
o	Tachycardia (via increased sympathetic activity
o	Increased BP
43
Q

What type of response to exercise do metaboreceptors give?

A

“Pressor Response” to exercise

44
Q

When are metaboreceptors especially important?

A

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

45
Q

What are contracted muscles supplied by due to metabolism?

A

o Contracted muscle supplied by dilated resistance vessels due to metabolism

CVS (17 decks)

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