CVS II > Specialised Circulations > Flashcards

Specialised Circulations Flashcards

(48 cards)

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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?

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A

blushing (sympathetic sudomotor nerves)

21
Q

What’s the Lewis triple response to skin injury?

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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?

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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

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A

Severe tissue necrosis

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

24
Q

How to avoid prolonged obstruction of flow by compression?

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A

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

25
Effect of postural hypotension / oedema due to gravity?
Standing for long periods in the hot reduces CVP (hypotension) + increases capillary permeability (oedema) Feel faint, rings on fingers can be tighter
26
Effect of Raynaud’s disease?
Sustained vasoconstriction to cold in fingers | Local tissue ischemia
27
Special requirements of pul circulation?
Gaseous exchange | Area for metabolic function
28
Why's gaseous exchange a special requirement of pul circulation?
Receives entire CO from RV Needs low pressure to do this Needs to occur very fast – not to be ‘diffusion-limited’
29
Why's an area for metabolic function a special requirement of pul circulation?
Receiving entire CO from RV means the pul circulation is a good system to produce or remove substance
30
Which special factors provides a huge O2 diffusion capacity?
``` -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
Special problems with pul circulation?
Gravity Chronic HPV Pulmonary oedema
32
How's gravity a problem with pul circulation?
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
How's chronic HPV a problem with pul circulation?
High altitude for long periods or respiratory disease eg COPD - hypoxia - vasoconstriction - pul hypertension - right ventricular failure
34
How's pul oedema a problem with pul circulation?
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
Special requirements of skeletal muscle circulation?
Exercise | Controls arterial pressure
36
Why's exercise a special requirement of skeletal muscle circulation?
Delivery of O2 and nutrients eg glucose must equal work | Blood flow must be proportional to exercise intensity
37
Why's arterial p a special requirement of skeletal muscle circulation?
- skeletal muscle is 40% of body mass - vascular resistance contributes to TPR - vasodilation + vasoconstriction of skeletal muscle circulation has sig changes in BP
38
Special structural feature of skeletal muscle + eg?
Capillary density differs in diff muscles: | Postural muscles capillary denisty > phasic muscles eg soleus always active > calf, forearm
39
Why does capillary density differs in diff muscles?
Endurance training increases capillary growth, | at a rate proportional to numbers of mitochondria per fibre
40
Special functional features of skeletal muscle circulation?
- High vascular tone - Metabolic vasodilatation - High expression of β2-adrenoceptors on VSM - O2 extraction
41
Effect of high vascular tone on skeletal muscle circulation?
- 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
Effect of metabolic vasodilation on skeletal muscle circulation?
``` Metabolic products (K+, adenosine, phosphate, H2O2) produce vasodilatation Relates exercise intensity to increased blood flow ```
43
Effect of high expression of β2-adrenoceptors on VSM on skeletal muscle circulation?
Stimulation of β2 by A --> vasodilatation
44
Effect of O2 extraction on skeletal muscle circulation?
- 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
Special problems of skeletal muscle circulation?
- Mechanical interference - Increased capillary pressure during exercise - Leg arteries major areas for atheroma
46
Effect of mechanical interference?
-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
Effect of increased capillary pressure during exercise?
-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
eg of leg arteries major areas for atheroma?
Ischemia leg pain, ulcers, gangrene
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