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Exercise & Environment > Venous circulation and posture > Flashcards

Venous circulation and posture Flashcards

1
Q

pressure

A

pressure is the force (N) applied perpendicularly to a surface per unit area (m^2) over which that force is distributed
1Pa = 1N/m^2

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2
Q

same force one a different area gives

A

different pressure

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3
Q

how are blood pressure values expressed

A

relative to atmospheric pressure

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4
Q

what is atmospheric pressure

A

760mmHg

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5
Q

what is blood pressure

A

100mgHg

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6
Q

what vessels have large diamaters

A
  • aorta
  • elastic arteries
  • muscular arteries
  • vena cava
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7
Q

what vessels have small diameters

A
  • arterioles
  • capillaries
  • venules
  • veins
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8
Q

what vessels have small total cross sectional area

A
  • elastic arteries
  • muscular arteries
  • vena cava
    (few of them)
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9
Q

what vessels have large total cross sectional area

A
  • arterioles
    -capillaries
    -venules
    -veins
    (lots of them)
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10
Q

which vessels blood pressure greatest

A
  • elastic arteries
  • muscular arteries
  • arterioles
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11
Q

which vessels in blood pressure lowest

A
  • capillaries
  • venules
  • veins
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12
Q

where is blood velocity greatest

A
  • elastic arteries
  • muscular arteries
  • vena cava
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13
Q

where is blood velocity low

A
  • arterioles
  • capillaries
  • venules
  • veins
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14
Q

what determines blood vessel compliance

A

how easy it is to increase they cross sectional area

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15
Q

which blood vessels are highly compliant

A

veins
they contain more than 60% total blood volume and are capacitance vessels
- they will decrease their capacity through vascular tone

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16
Q

what are capacitance vessels

A

veins - they have the ability to store charge

and so can decrease their capacity through vascular tone because

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17
Q

where do veins carry blood

A

back to the heart.

all valves in veins allow blood flow only toward to heart

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18
Q

what blood vessels carry blood to the heart

A

veins

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19
Q

resting muscle blood flow

A

only a few capillaries open at any one time

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20
Q

exercising muscle blood flow

A 
vasodilation
- more capillaries open
- higher blood velocity
- double the fall in oxygen saturation 
Capillary recruitment contributes to reduces the diffusion distance so that the muscle can consume more than 40times the oxygen during exercise
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21
Q

blood flow redistribution

A

CO increases with exercise intensity an blood flow is redistributed to provide a large proprtionof blood to skeletal muscle and some to skin for thermoregulation

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22
Q

what must be maintained during blood reflow redistribution

A

Blood pressure

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23
Q

hydrostatic pressure

A

drives flirtation out of the capillary, when pressure is greater in the tissue than in surrounding tissues

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24
Q

osmotic pressure

A

drives absorption into tissues from surrounding tisses

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25
Q

how is blood volume increased after large blood loss

A

Osmotic pressure will drive absorption into capillaries from surrounding tissue

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26
Q

how much plasma enters capillaries daily

A

4000L

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27
Q

net daily filtration at capillaries

A

8l

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28
Q

where does blood filtration occur

A

capillaries

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29
Q

what happens to 8L of net filtration

A

returned to the vascular compartment through lymphatic system

30
Q

how much blood enters capillaries per day

A

7200L

31
Q

what happens to plasma volume during exercise

A

whole body plasma can decrease by 16-20%

  • active muscles gain fluid during excercise
  • muscles swell by 20% within 15 minutes of exercise
32
Q

orthostasis

A

standing p

33
Q

standard blood pressure

A

120/80 mmHG

34
Q

standard blood pressure measured at leg

A

220/160 mmHG

35
Q

mercury compared to water

A

mercury is 13.6 times denser than water

36
Q

why is BP greater at leg than arm when standing

A

weight of the column of blood increases arterial blood pressure

37
Q

filtration during orthostasis

A

40 mites of standing can induce a reduction in plasma volume by 6-12 %
- increased blood pressure
- causes increased filtration
= feet swelling if standing or sitting for prolonged period of time

38
Q

how to reduce swelling in feet when sitting for prolonged time

A

compression socks, which reduce the pressure gradient between capillaries and surrounding tissues

39
Q

myogenic regulation

A

local compensatory response to changes in blood pressure

40
Q

how does a rise in BP effect myogenic regulation

A

contraction of vessels because there is an excessive oxygen delivery from raised BP

41
Q

how does a fall in BP effect myogenic regulation

A

dilation of vessels because there is limited supply of oxygen from fall in BP

42
Q

what ensures the brain recieves the correct amount of oxygen

A

passive redistribution

ensures the brain does not receive excessive or insufficient oxygen, despite changes in BP

43
Q

BP studies on rabbits, cats and dogs

A 
nerve excitation causes:
 - rapid increase in BP
- rapid increase in blood volume
when excitation stops
- BP returns to pre sitmaultion value
- leg volume returns to pre stimulation value and transiently goes greater than pre value
44
Q

does myogenic regulation of BP require CNS

A

no, it is a local mechanism and can be performed in muscle post mortem therefore CNS not needed

45
Q

increased BP on post mortem blood vessel

A
  • increased BP causes transient increase in diameter
  • maintained high BP and diameter will contract for during of increased prssure
    this keeps flow relatively un altered
46
Q

what is the skeletal muscle pump

A

local compensatory response to increased blood pressure
- contracting calf muscles help blood flow back to the heart
- lowers venous foot pressure by 20-30mmHg
The calf muscle acts as pump for deep leg veins
- when calf muscle relaxed, blood flows and toward feet but stopped by valves
when calf contracts, blood is forced back towards heart and pushes valves open to do so

47
Q

how does postural change affect blood volume

A
  • big changes in veins and arterioles
  • standing causes blood pressure to rise in arterioles and veins from pooling of blood at feet
  • pooling of blood in lower extremities results in orthostatic pressure changes
    BUT the pressure gradient between arterioles and veins remains the same = 86mmHg
  • blood flow is not affected by gravity
48
Q

what is the pressure gradient between arterioles and veins

A

86mmHg

49
Q 
pressure when standing:
right atrium
aorta
veins at feet 
arterioles at feet
A 
pressure when standing:
right atrium 4mmHg
aorta 100mgHf
veins at feet 100mgHg
arterioles at feet 186mmHg
50
Q 
pressure when supine:
right atrium
aorta
veins at feet 
arterioles at feet
A 
pressure when supine:
right atrium 4mmHg
aorta 100mmHg
veins at feet 10mmHg
arterioles at feet 96mmHg
51
Q

cardio vascular response to orthostasis

A
  • increase in HR
  • decrease in central venous pressure
  • decrease in cardiac end diastolic volume
  • decrease in stroke volume and cardiac output
  • decrease in pulse pressure
  • increase in total peripheral resistance
52
Q

central venous pressure relates to what volume

A

intra-thoracic blood volume

53
Q

intra-thoracic blood volume relates to what pressure

A

central venous pressure

54
Q

what reflex sensors detect BP changes

A

aortic arch and carotid sinus baroreceptors discharge with each beat of the heart and sense changes in BP

55
Q

reflex response to fall in BP

A
  • aortic arch and carotid sinus baroreceptors have a reduced rate of AP caused by fall in BP
  • this induces increase in sympathetic discharge
  • # and decrease in parasympathetic discharge
  • increased HR
  • arteriolar vasoconstriction in skeletal muscle and kidney
  • venous vasoconstriction
56
Q

how do parasympathetic and sympathetic discharges change in response to drop in BP

A
  • sympathetic increase

- parasympathetic decrease

57
Q

autonomous nervous system response to orthostasis

A
  • mean arterial BP transiently decreases but restored by reflexes short term
    = transient hypotension which reduces cerebral perfusion causing dizziness
  • vagus nerve mediates lowering of HR via stimulation of SA node
    = reduction of parasympathetic vagal outflow to reduce HR
  • increased outflow of sympathetic nerves increase HR and contractility and determine vasoconstriction
  • coordianted increase in HR, TPR and MABP limit the fall of cardiac output to ~20%
    = limited variability of cerebral perfusion during postural changes
58
Q

how does reduced parasympathetic vagal outflow effect HR

A

increases HR. occurs in response to standing to prevent fainting

59
Q

how does increased sympathetic nerve output effect CV

A

increases HR, contractility and determines vasoconstriction to increase TPR

60
Q

how is fall in cardiac output limited during orthostasis

A

coordinated increase in HR, TPR and MABP

61
Q

how much does CO fall during orthostasis

A

~20%

62
Q

what is the overall effect of local and reflex responses to postural changes

A

limits variability of cerebral perfusion

63
Q

difference in ventricles and arterioles of foetus and adult giraffe

A

both are hypertrophied in adult compared to foetus

64
Q

what is fainting

A

sudden, transient loss of consciousness

observed when cerebral blood flow decreases to ~less than half normal value bc of decreased arterial pressure

65
Q

what causes decrease in cerebral blood flow

A

decreased arterial pressure

66
Q

what causes fainting

A
  • blood volume redistribution during orthostasis
  • blood volume reduction, hypovolaemia
  • psychological stress
  • combination of the above
67
Q

what are the initial CV effects of stress

A

induces alarm response:

  • tachycardia
  • muscle vasodialtion
  • cutaneous vasoconstriction
  • hyperventilation
68
Q

what follows the alarm response to stress

A 
increased vagal outflow which causes:
- bradycardia
-drop in peripheral resistance
- drop in arterial BP
- drop in cerebral perfusion 
= loss of consciousness
= vaso-vagal episode
69
Q

what restores consciousness

A

supine position - hence naturally occurs when you faint

70
Q

vaso-vagal episode

A

temporary fall in BP related to fainting

Exercise & Environment (14 decks)

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