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CVS II > Specialised Circulations > Flashcards

Specialised Circulations Flashcards

1
Q

Special requirements of cutaneous circulation?

A
  • Defence against environment
  • Temp regulation
  • Lewis triple response to trauma
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2
Q

How does skin regulate temp?

A

Radiation (skin vs ambient temp)
Conduction - skin onto other object
Convection - removal by air/water
Sweating (latent heat of evaporation)

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3
Q

What does skin temp depend on?

A

Skin blood flow

Ambient temp

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4
Q

How’s the skin a poikilo-thermic organ?

A

temp ranges from 0 -40oC briefly w/o damage for short periods of time

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5
Q

Special structural feature of skin?

A

Arterio-Venous Anastomoses (AVAs)

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6
Q

What are arterio-venous anastomoses (AVAs)?

A

Direct connections of arterioles + venules – expose blood to regions of high SA

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7
Q

What controls arterio-venous anastomoses (AVAs)?

A

Sympathetic vasoconstrictor + sudomotor vasodilator fibres driven by temp regulation nerves in hypothalmus

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8
Q

Special functional features of skin?

A
  • Responsive to ambient + core temperatures
  • Severe cold causes ‘paradoxical cold vasodilatation’
  • Core temp receptors in hypothalamus control sympathetic activity to skin –> blood flow
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9
Q

Effect of increased ambient temp?

A

vaso + venodilation helping heat loss

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10
Q

Effect of decreased ambient temp?

A

vaso + venoconstriction conserving heat

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11
Q

Why’s there cold-induced vasoconstriction?

A

Conserves heat because:

  • abundance of α2 receptors
  • ↓ AC/cAMP/PKA on VSMCs in skin
  • bind NA at lower temp than α1 receptors
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12
Q

What pathway is α2 receptors?

A

Gi so reduces AC/cAMP/PKA

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13
Q

Why’s there paradoxical cold vasodilatation

A

Protect from skin damage:

  • caused by paralysis of sympathetic transmission
  • long-term exposure leads to oscillations of contract/relax
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14
Q

How does core temp regulate blood flow to skin?

A
  • increased core temp
  • stimulate warmth receptors in anterior hypothalamus
  • sweating + vasodilation
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15
Q

Describe sweating from increased core temp

A

increased sympathetic activity (Ach) to sweat glands

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16
Q

Describe vasodilation from increased core temp

A

increased sympathetic sudomotor activity (Ach act on endothelium to produce NO) to arterioles in extremities

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17
Q

Baroreflex/RAAS/ADH-stimulated vasoconstriction of skin blood vessels

A

-haemorrhage, sepsis, acute cardiac failure
-drop in BP
-so blood directed to vital organs/tissues during
-mediated by sympathetic vasoconstrictor fibres + A +
ADH + Ang II

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18
Q

Why’s a patient pale cold skin in shock?

A

Baroreflex/RAAS/ADH-stimulated

vasoconstriction of skin blood vessels

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19
Q

What happens if somebody with a haemorrhage is warmed up too quickly?

A
  • warm up body too quickly
  • reduce cutaneous vasoconstriction
  • blood flow to skin not vital organs/tissues
  • dangerous
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20
Q

eg of emotional communication?

A

blushing (sympathetic sudomotor nerves)

21
Q

What’s the Lewis triple response to skin injury?

A

Local redness: Site of trauma
Local swelling: Inflammatory oedema (wheal)
Spreading flare: Vasodilatation spreading out from site of trauma

22
Q

Importance of Lewis triple response to skin injury?

A

Increased delivery of immune cells, antibodies to site of damage to deal with invading pathogens

23
Q

Effect of prolonged obstruction of flow by compression + eg

A

Severe tissue necrosis

‘bed sores’; heals, buttocks, weight bearing areas

24
Q

How to avoid prolonged obstruction of flow by compression?

A

Shifting position causing reactive hyperaemia (on removal of compression)
High skin tolerance to ischemia

25
Q

Effect of postural hypotension / oedema due to gravity?

A

Standing for long periods in the hot reduces CVP
(hypotension) + increases capillary permeability (oedema)
Feel faint, rings on fingers can be tighter

26
Q

Effect of Raynaud’s disease?

A

Sustained vasoconstriction to cold in fingers

Local tissue ischemia

27
Q

Special requirements of pul circulation?

A

Gaseous exchange

Area for metabolic function

28
Q

Why’s gaseous exchange a special requirement of pul circulation?

A

Receives entire CO from RV
Needs low pressure to do this
Needs to occur very fast – not to be ‘diffusion-limited’

29
Q

Why’s an area for metabolic function a special requirement of pul circulation?

A

Receiving entire CO from RV means the pul circulation is a good system to produce or remove substance

30
Q

Which special factors provides a huge O2 diffusion capacity?

A 
-High capillary density :
Over 100 m2 area of capillaries in lungs
Continuous sheet of blood
-Short distance between capillary + alveolar :
0.3 µm so fast diffusion
31
Q

Special problems with pul circulation?

A

Gravity
Chronic HPV
Pulmonary oedema

32
Q

How’s gravity a problem with pul circulation?

A

Upright : low pul arterial pressures at lung apex
MPA pressure – 15 mmHg, Apex – 3 mmHg, Base – 21 mmHg
Poor perfusion at apex –> vessel collapse
Standing person slightly impaired blood oxygenation

33
Q

How’s chronic HPV a problem with pul circulation?

A

High altitude for long periods or respiratory disease eg COPD

  • hypoxia
  • vasoconstriction
  • pul hypertension
  • right ventricular failure
34
Q

How’s pul oedema a problem with pul circulation?

A

Thinness of capillary-alveoli means potential for stress + leak eg mitral valve stenosis

  • increased pressure in LA
  • increased pulmonary capillary pressures
  • increased filtration
  • oedema
  • poor lung function
35
Q

Special requirements of skeletal muscle circulation?

A

Exercise

Controls arterial pressure

36
Q

Why’s exercise a special requirement of skeletal muscle circulation?

A

Delivery of O2 and nutrients eg glucose must equal work

Blood flow must be proportional to exercise intensity

37
Q

Why’s arterial p a special requirement of skeletal muscle circulation?

A
  • skeletal muscle is 40% of body mass
  • vascular resistance contributes to TPR
  • vasodilation + vasoconstriction of skeletal muscle circulation has sig changes in BP
38
Q

Special structural feature of skeletal muscle + eg?

A

Capillary density differs in diff muscles:

Postural muscles capillary denisty > phasic muscles eg soleus always active > calf, forearm

39
Q

Why does capillary density differs in diff muscles?

A

Endurance training increases capillary growth,

at a rate proportional to numbers of mitochondria per fibre

40
Q

Special functional features of skeletal muscle circulation?

A
  • High vascular tone
  • Metabolic vasodilatation
  • High expression of β2-adrenoceptors on VSM
  • O2 extraction
41
Q

Effect of high vascular tone on skeletal muscle circulation?

A
  • Reduces BF at rest enabling vasodilatation during exercise to increase BF
  • Reduces BF to capillaries at rest enabling capillary recruitment (vasodilatation) to increase SA + BF for exchange
42
Q

Effect of metabolic vasodilation on skeletal muscle circulation?

A 
Metabolic products (K+, adenosine, phosphate, H2O2)
produce vasodilatation
Relates exercise intensity to increased blood flow
43
Q

Effect of high expression of β2-adrenoceptors on VSM on skeletal muscle circulation?

A

Stimulation of β2 by A –> vasodilatation

44
Q

Effect of O2 extraction on skeletal muscle circulation?

A
  • during exercise increased from 25-30% to 80-90%
  • increased blood flow
  • increased area for exchange
  • reduced distance for exchange
  • muscle cells using lots more O2
45
Q

Special problems of skeletal muscle circulation?

A
  • Mechanical interference
  • Increased capillary pressure during exercise
  • Leg arteries major areas for atheroma
46
Q

Effect of mechanical interference?

A

-muscles contract
-reduce blood flow in intra-muscle vessels
-good in rhythmic exercise eg running
BUT
-sustained contraction eg carry bagss
-poor O2 supply
-anaerobic respiration
-build up of lactate
-muscle fatigue

47
Q

Effect of increased capillary pressure during exercise?

A

-during exercise increased BF to muscles
-increased capillary pressure
-increased filtration of plasma volume into muscles
-oedema
eg pumped muscle reduces plasma volume by 10%

48
Q

eg of leg arteries major areas for atheroma?

A

Ischemia leg pain, ulcers, gangrene

CVS II (19 decks)

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