CVS II > Coordinated CVS Responses > Flashcards

Coordinated CVS Responses Flashcards

(42 cards)

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1
Q

Describe immediate effect of standing up (orthostasis)

A
  • CVS changes according to effect of gravity
  • gravity pulls blood
  • less CVP
  • less Starling’s law
  • less CO
  • BP falls at first (postural hypotension)
  • lack of drive of flow to brain
  • can cause fainting
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2
Q

How to recover from standing up (orthostasis)?

A

homeostatic mechanisms (baroreflex)

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3
Q

How to modulate homeostatic mechanisms (baroreflex)?

A

Increase in:

  • HR
  • Ventricular contractility (maintains SV/CO despite less blood returning to heart)
  • TPR (+constriction of veins)
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4
Q

What happens to BP in supine position + why?

A
  • Head, heart, feet constant as tube of blood horizontal
  • Venous system p equal in head + feet
  • Lower venous system p in heart where large veins due to less resistance (vital as helps blood flow back to heart)
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5
Q

What happens to BP when standing up + why?

A

-Effect of gravity
-Arterial system mean BP similar
-In head BP lower
-Feet higher BP
-Venous system p in feet high
-Low venous system p to heart
So in the feet:
Arterial p increased from 95 to 185 mmHg now standing
Venous p increased from 10 to 90 mmHg

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6
Q

Why does arterial blood flow down to feet + not up to

heart?

A

Blood higher up in arteries have higher potential energy Arterial system 95mmHg pushing blood down + potential energy caused by gravity (exerting around 90-100mHg) so small p diff between feet + heart
but large vessels to feet allow movement despite small p diff

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7
Q

How blood moves back up to heart?

A

increased potential energy at heart vs feet + increased kinetic energy of ejected blood

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8
Q

Why does gravity induce high BP in venous systems?

A

blood vessels in our leg are like tubes with

fluid in it that have diff pressures at diff depths depending on height of fluid column

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9
Q

What’s Bernoulli’s law?

A

BF = p energy + potential energy + kinetic energy

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10
Q

Why is fluid at bottom of tube under greater pressure than at top?

A

Pressure = ρhg
ρ : fluid density
h : height (of fluid column)
g : gravitational acceleration constant (gravity)

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11
Q

Why’s there pooling of blood in lower extremities?

A

veins are distensible so under pressure they stretch + increase in volume

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12
Q

Effect of pooling of blood in lower extremities on BP?

A

causes the drop in BP as less is going back to the heart

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13
Q

Why do veins expand with increased p?

A

veins are distensible so increase in p isn’t used to push

blood forward so exerted in walls expanding the veins

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14
Q

Describe how standing up decreases BP

A
  • stand up
  • pooling of blood (+500ml) in legs
  • increases transmural p
  • less BF back to heart
  • decrease CVP + EDV
  • less Starling’s law + SV
  • less CO
  • decrease in BP
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15
Q

How does orthostasis cause hypotension?

A
  • causes fall in CVP
  • decreased stroke volume (Starling’s)
  • decreased CO
  • decreased BP
  • poorer perfusion of brain
  • dizzy, fainting
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16
Q

What measures drop in BP?

A

Mechanoreceptors in atria + ventricles

Baroreceptors in aortic arches + carotid sinus

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17
Q

Reflex response to orthostasis?

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A
  • decrease in BP
  • switches off afferents going back to nucleus tractus soltarius
  • decrease in input to nucleus tractus soltarius.
  • decrease stimulation of CVLM
  • switches off its inhibitory pathway to the RVLM.
  • excitatory fibres from RVLM switched on
  • increases sympathetic drive to:
  • SAN = ↑ pacemaker potential + HR
  • Myocardium = ↑ contractility
  • Resistance vessels = ↑ contraction so ↑ TPR
  • Capacitance vessels (veins) = helps venous return
  • decreases vagal inputs to SAN
  • reduced bradycardic effects of vagus nerve on SAN
18
Q

What makes postural hypotension worse?

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A

-α-adrenergic blockers/VGCC blockers
-Varicose veins = impaires venous return –> lower CVP –> lower BP
-Lack of skeletal muscle activity from paralysis or forced inactivity = can’t use skeletal muscle pump, so
decreasing return to heart
-Reduced circulating blood volume / haemorrhage = less blood back to heart
-Heat = causes peripheral vasodilatation so blood to skin so less to heart eg standing up after a hot bath causes dizziness

19
Q

Effect microgravity (space) on CVS?

Study These Flashcards
A
  • Standing or lying down same in microgravity

- Less need for ANS, RAAS, ADH, ANP systems to control BP as no gravity

20
Q

Describe initial effect of mictogravity on redistribution of blood into chest region?

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A
  • Initially:
  • less blood to lower extremities
  • increase preload
  • increase atria/ventricle volume
  • increased SV sensed by cardiac mechanoreceptors
  • decreased sympathetic by more stretching of the receptors
  • NS, RAAS, ADH + Increased GFR, ANP
  • diuresis (water loss)
  • lower blood volume by 20%
21
Q

Describe long-term effect of mictogravity on redistribution of blood into chest region?

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A
  • less BV
  • reduced stress on heart
  • heart reduces in muscle mass
  • drop in BP
22
Q

Describe effect after effects of mictogravity on redistribution of blood into chest region?

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A
  • severe postural hypotension
  • smaller heart
  • low blood volume
  • baroreceptor reflex cannot compensate
  • takes time for normal baroreceptors to reach former threshold
23
Q

Diff between dynamic vs static exercise + eg?

Study These Flashcards
A 
Continuous contraction + relaxation (running)
Just contracting (lifting weight)
24
Q

Purpose of CVS during exercise?

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A
  • ↑ pul circulatory O2 uptake
  • ↑ O2 transport
  • Direct increased O2 supply to exercising muscle
  • Maintain BP despite increase in CO by changing TPR (prevent afterload + reduced output of heart)
25
Reflex of muscle mechanoreceptors?
- Respond to movement in muscle - Decreases vagal activity - Prevents heart being slowed down - Respond to increased metabolites in response to exercise - Increases sympathetic
26
eg of integration?
O2 uptake by pul circulation which increases 13x during strenuous exercise
27
Small integrations response to exercise?
- ↑ HR - ↑ SV - ↑ CO - ↑ arterio-venous O2 diff due to more O2 being removed from blood by muscle so helps gradient to get oxygen into pul circulation + get O2 out into tissues
28
How is O2 uptake from lungs increased?
- pulmonary BF = CO - increases with exercise - O2 consumption increases - same saturation of blood - more blood going to lungs picking up more O2 - tissues extract more O2 - greater arterio-venous O2 diff
29
Describe how greater arterio-venous O2 diff is done
- increasing BF to skeletal muscle - increases capillary recruitment - more area for O2 uptake + shorter distance - quicker passive diffusion - more extraction of O2 into tissue
30
Describe how increased cardiac output is done
- HR increases gradually for strenuous exercise - provides extra CO needed - SV increases rapidly for light exercise - harder exercise HR starts to take over - SV plateaus - starts to decrease as BP increases - greater afterload
31
What's the potential increase of HR?
3x 220 – Age eg 30yr has max HR change of 65 - 190bpm
32
How HR increased?
due to central command getting body for exercise + muscle metaboreceptors/mechanoreceptors -increases HR by decreasing vagal para: removes vagal tone setting resting HR at SAN effecting conduction speed of AVN -increase in sympathetic: drive increase in HR (acting at SAN + AVN) -release of adrenaline (catecholamines) acting at β1 on heart
33
Why's driving increase in HR vital in transplant patients?
lost innervation of heart from sympathetics so rely fully on adrenaline/NA to increase HR
34
How much does SV increase?
- increase in sympathetic - increase in SV - 30yr SV 70ml to 105ml (1.5x increase)
35
Describe how increased SV is done?
-increase in sympathetic causes venoconstriction -increase venous return (CVP) to heart -if using calf muscle pump drives venous return. -Starling’s law: small increase in end-diastolic volume so greater contractility so greater SV -sympathetics also cause increase in contractility via activating β1 -Ca2+ influx -cardiac myocytes = increase contractility (inotropic effect) -faster contraction -decrease in end-systolic volume (increase in ejection fraction) -ejecting more from a full chamber so increase in SV Remember the equation: CO = HR x SV
36
Why's CO increased?
-increase in CO (increase of 4.5x, 5 to 22l/min) can be accounted for by increase in HR (3x) + increase in SV (1.5x)
37
Describe how increased CO targets muscle during exercise?
- increase CO - more blood oxygenated - target flow/CO to right tissue - A binds to β2 --> vasodilation - fall in local resistance in vascular skeletal muscle arterioles - also metabolic vasodilatation. - vasodilatation of active muscle, myocardium, skin during exercise increases BF
38
Describe what happens to BP when CO increases by X4.5?
-BP = CO x TPR so expect to increase HOWEVER -increases slightly when exercising heavy. -diastolic pressure unchanged -systolic increases due to increased power of contraction -increase in CO so large drop in TPR due to vasodilatation in muscle -so can exercise hard +long but keep BP same so heart can pump against a reasonable BP
39
Role of RVLM?
controls specific pre-ganglionic symp nerves in spinal cord which send out post-ganglionic nerve to specific tissues
40
What prevents hypotension due to exercise-induced drop in TPR?
-compensatory vasoconstriction in inactive tissues prevents BP falling -BF decrease in splanchnic vessels, kidneys, other inactive muscles occurs via α1 -huge increase in flow to lungs
41
Why do static exercises raise BP more than dynamic exercises?
- Dynamic big increase in HR due to contract+relax continuously - Static HR increases slightly, but BP increase a lot due to muscle contracted constantly, so BF to muscle prevented + low, build up in metabolites, so increase drive of blood to tissue increasing BP
42
Describe metaboreceptors
-static exercise = mechanoreceptors (small diameter sensory fibres) activated in muscle, metaboreceptors (chemosensitive) recognise rise in metabolites(K+, H+, lactate) --> stimulate symp to increase BP (pressor response to exercise) + slight tachycardia to maintain perfusion to contracted muscle Especially occurs in isometric exercises (increased muscle load)
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