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specialised circulations Flashcards

1
Q

Cutaneous circulation - special requirements

3 key features?
temp skin can range from?

A

Defence against the environment

Temperature regulation – blood flow delivers heat from body core

Skin is a poikilo-thermic (not homeo-) organ
Its temperature can range from 0oC to 40oC (briefly)
without damage for short periods of time

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2
Q

How does body transfer heat?

4 ways (how?)

A

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

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3
Q

what does skin temperature depend on? (2)

A

skin blood flow

ambient temperature

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4
Q

Cutaneous circulation - special structural features

what are AVAs? what do they have and do? why?

A

Arterio-Venous Anastomoses (AVAs) - Direct connections of arterioles and venules –> expose blood to regions of high surface area

AVAs where blood flow is directed from the arterioles into the venous system which is more compliant therfore can hold more blood and acts as a blood reservoir -> more blood will be at skin so we can lose heat

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5
Q

How is blood directed from arterioles to AVAs?

what innervations are needed?
what two fibres work together? and how?

A

sympathetic vasoconstrictor will vascoconstrict at aterioles and decrease blood flow there

sudomotor vasodilator fibres will dilate and increase blood flow into AVAs

Both are sympathetic innervations to increase blood flow to veins so it holds more blood and more blood is lost

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6
Q

What controls blood flow to AVAs?

how does it act?

A

Driven by temperature regulation nerves in hypothalmus

Core temperature receptors in hypothalamus control sympathetic activity to skin & hence skin blood flow

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7
Q

Cutaneous circulation - special functional features

what does it respond to?
how does it change?
what is the paradox?

A

Responsive to ambient & core temperatures

Increased ambient temperature causes vaso- and venodilatation -> helps heat loss

Decreased ambient temperature causes vaso- and venoconstriction -> helps to conserve heat

Severe cold causes ‘paradoxical cold vasodilatation’

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8
Q

20 mins period of local cooling by ice - first 10 mins

what happens?
why?
how does it do this?
significance of the receptors?

A

Cold-induced vasoconstriction
To conserve heat

Caused by abundance of
a2 receptors (decreased AC/cAMP/PKA – switch off vasorelaxation processes) on VSMCs in skin
Bind NA at lower temperatures than α1 receptors

a2 receptors work well in cold
NA released by sympathetic nerves act better on a2 than a1 receptors hence why hand will go pale

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9
Q

20 mins period of local cooling by ice - last 10 mins

what happens?
why?
how?
what happens during long term exposure?

A

Paradoxical cold vasodilatation
To protect skin damage

Caused by paralysis of sympathetic transmission
(less NA released) hence a2 receptors not stimukated as much and there is more vaso-dilation

Long-term exposure leads to oscillations of contract/relax

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10
Q

Increased cutaneous perfusion with increased cored temperature (e.g. exercise)

what detects this?
what two key effect take place to reduce temp?

A

Increased Core temp
Stimulate warmth receptors in anterior hypothalamus
causes:

Sweating
Increased sympathetic activity (Ach) to sweat glands

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

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11
Q

Cutaneous circulation - special feature
Baroreflex/RAAS/ADH-stimulated vasoconstriction of skin blood vessels

importance of this?
mediated by? what does it cause?
what does this look like on the person?

A

If drop in BP following haemorrhage, sepsis, acute cardiac failure need more blood flow to the organs which potentially could get under perfused hence shift blood flow to these organs via switching off blood flow to our skin

Mediated by sympathetic vasoconstrictor fibres
+ adrenaline + vasopressin + angiotensin II which all cause vasoconstriction of blood vessels of skin

it causes - pale/cold skin of patient in shock

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12
Q

why heating up body after haemorrhage is bad?

what happens to body when you heat it up? why is this bad?

A

During haemorrhage – warm up body too quickly – reduce cutaneous vasoconstriction – blood flow to skin not vital organs/tissues - potentially dangerous

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13
Q

emotional communication - what happens and how?

A

e.g. blushing (sympathetic sudomotor nerves)

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14
Q

Lewis triple response of skin to trauma

what is the triple response?

how does it work?
what will the trauma stimulate and where do these fibres go? where do some collateral fibres go? what do these release? what do they act as and cause?

A

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

trauama will stimulate c fibres which go to the spinal cord and help us recognise pain and collateral come off c fibres which cause the release of neuromodulators such as substance P + substances that stiumukate mast cells which release histamine

BOTH act as vasodilators which cause a flare response therfore more vasodilation, more blood flow to trauma and more immune cells to area.

inflammatory oedema due to increased blood flow therefore more fluid moving out of blood and into local interinterstitial fluid

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15
Q

Cutaneous circulation - special problems
prolonged obstruction of flow by compression

why does laying in bed for lomg periods of time cause ischemia? what can it lead to?

how can this be avoided? (2)

A

Laying in bed for a long period of times, you compress blood flow to the skin can lead to ischemia
Severe tissue necrosis
‘bed sores’; heals, buttocks, weight bearing areas

Avoided by:
Shifting position / turning causing reactive hyperaemia hence will get blood flow back to area (on removal of compression)
High skin tolerance to ischemia

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16
Q

Cutaneous circulation - special problems
postural hypotension/oedema due to gravity

what happens when you stand for long periods of time in hot weather? what effect will this have on body which can lead to fainting?

what causes the oedema?

A

Often standing for long periods in hot weather will decrease CVP (hypotension) as in hot weather, body will try to cool down therefore vasodilate which will take up lots of venous return and shift to skin hence less blood in venous system/less return to rhs of heart therefore less stalin law and less co therefore hypotension and less perfusion to the brain which can lead to fainting

increased capillary permeability (oedema) due to gravity too
Feel faint, rings on fingers can be tighter

17
Q

Cutaneous circulation - special problems
Raynaud’s disease

what is it?

A

Sustained vasoconstriction to cold in fingers

Local tissue ischemia

18
Q

Pulomonary circulation - special requirements

what takes place here?
what does it recieve and what does it need for this process to take place?
what stops the process from being ‘diffusion-limited’?

what is this area good for?
why?

A

Gaseous exchange
Receives entire cardiac output from right ventricle
Needs low pressure to do this
Needs to occur very fast – not to be ‘diffusion-limited’
(if slow, law of blood flow may allow o2 to move back into lungs)

Area for metabolic function
Receiving entire cardiac output from right ventricle means the pulmonary circulation is an excellent system to produce or remove substance

19
Q

Pulomonary circulation - special features structural

2 key features
what do they work together to provide?

A

Very high capillary density
Over 100 m2 area of capillaries in the lungs
Continuous sheet of blood

Very short distance between capillary and alveolar – 0.3 µm -> Very fast diffusion

Together, these factors provide huge ‘Oxygen Diffusion Capacity’

20
Q

Pulomonary circulation - special features functional
Low vascular resistance

what does this aid?

A

1/8 of normal systemic vascular resistance, less sympathetic influence
20-25 to 8-12 mmHg is systole and diastole
Low pressure system aids gaseous exchange

21
Q

Pulomonary circulation - special features functional
Hypoxia pulomonary vasoconstriction (HPV)

what does hypoxia lead to in systemic circulation?
what about pulmonary circulation? why?
how does it do this?

A

In systemic circulation, a drop in O2 levels (Hypoxia) leads to vasodilation, termed metabolic hyperaemia
Not in pulmonary circulation, hypoxia causes vasoconstriction, why?
Vasoconstriction prevents blood to poorly ventilated regions of lungs
Optimizing ventilation/perfusion ratio
How? Complicated……hypoxia increases excitability and contractility of vascular smooth muscle

22
Q

Pulomonary circulation - special features functional
metabolic functions

what does it remove and what does it use to produce a certain key molecule?

A

Receives all CO from RV
Contains ACE to produce Ang II and remove bradykinin/5-HT/NA
(ace found on pulmonary surface - RAAS system)

23
Q

Pulomonary circulation - special problems
Gravity

what happens to the apex of a lung when a person is standing upright?

what does this lead to? (2 reasons why)

does standing person provide blood to all of lungs?

A

In the upright, standing person the pulmonary arterial pressures at the apex of the lung (top part) are low – due to gravity
MPA pressure 15 mmHg, Apex 3 mmHg, Base 21 mmHg

Poor perfusion are apex leads to vessel collapse. Also, less vascular resistance in the walls of the pulomonary circulation therfore more compliant and can lead to vessel collapse

Standing person slightly impaired blood oxygenation as can’t provide blood flow to all of lungs

24
Q

Pulomonary circulation - special problems
Chronic HPV

what does chronic hypertension lead to in pulomonary circulartion? (4)
why?

A

High altitude for long periods, or respiratory disease such as COPD
– hypoxia - vasoconstriction – pulmonary hypertension – right ventricular failure

chronic hypertension cause back pressure in pulmonary circulation which can cause back pressure into RV as blood may stay there

25
Q

Pulomonary circulation - special problems
Pulmonary oedema

how can mitral stenosis lead to pulomary oedema?
why is lungs susceptible to oedema?

A

Thinness of capillary-alveoli interactions means potential for stress and leak -> being very thin means an increase in pressure can easily allow fluid to come out
e.g. Mitral valve stenosis, increased pressure in left atrium,
increased pulmonary capillary pressures, increased filtration, oedema
Poor lung function

26
Q

skeletal muscle circualtion - special requirements

what needs to happen during exercise?

what does skeltal muscle control in the circulation? why does it have a significant effect?

A

Exercise
Delivery of O2 and nutrients, e.g. glucose must equal the work carried out
Blood flow must be proportional to exercise intensity

Controls arterial pressure
Skeletal muscle makes up 40% of body mass
So, vascular resistance is a major contributor to total peripheral resistance Hence vasodilation and vasoconstriction of skeletal muscle circulation can have profound changes in blood pressure

27
Q

skeletal muscle circualtion - structural features

which muscles have higher capillary density?
how to increase capillary density?

A

Capillary density differs in different muscles
Postural muscles, e.g. soleus, always active
Higher capillary density than phasic muscles, e.g. calf, forearm
Endurance training increases capillary growth,
at a rate proportional to numbers of mitochondria per fibre therefore more blood flow to that tissues and can meet the demands of endurance training

28
Q

skeletal muscle circualtion - functional features
High vascular tone

what happens to blood flow at rest? why?
what about flows to capillaries? significance of this?

A

Reduces blood flow at rest, enabling significant vasodilatation to occur during exercise to increase blood flow

Also, reduces blood flow to capillaries at rest, switching them off
During vasodilatation, capillary recruitment, further increasing blood flow, surface area etc for gaseous exchange

29
Q

skeletal muscle circualtion - functional features
Metabolic vasodilation

examples of metabolic prooducts
what effect do they have?
what is the significance of this effect?

A 
Metabolic products - K+, adenosine, phosphate, H2O2
produce vasodilatation (products made from skeletal muscle hence more muscle used, more metabolite produced and more blood flow)
Relates exercise intensity to increased blood flow
30
Q

skeletal muscle circualtion - functional features
High expression of B2-adrenoceptors on VSM

what stimulates B2 receptors and what does it lead to?
what resposne takes place during exercise?

A

Stimulation of B2 receptors by adrenaline leads to vasodilatation

during exercise there is a sympathetic response hence increased HR/contractility and also increased adrenaline released which will act on B2 receptors which will open up skeletal muscle aterioles and allow more blood flow to musclesas we recruit more capillaries we don’t norammly use when we open up vessels hence more area for exchange to occur

31
Q

skeletal muscle circualtion - functional features
o2 extraction

how does this change during exercsie?
what 3 things allow this to happen?

A

Increased from 25-30% to 80-90% during high intensity exercise
Due to increased blood flow, increased area for exchange, reduced distance for exchange and muscle cells using lots more O2

32
Q

skeletal muscle circualtion - special problems
mechanical interference

what happens when muscles contract? when is this okay? when is this an issue? what does it lead to?

A

When muscles contract, reduce blood flow in intra-muscle vessels
Ok, in rhythmic exercise, e.g. running

Sustained contraction, e.g. carried heavy bags,
means poor O2 supply, anaerobic respiration,
build up of lactate, muscle fatigue

33
Q

skeletal muscle circualtion - special problems
increased capillary pressure during exercise

what does increased blood flow to muscles during exercise lead to?

A

Increased blood flow to muscles during exercise leads to increased capillary pressure, increased filtration of plasma volume into muscles
Oedema
e.g. ‘pumped’ muscle
Reduced plasma volume by 10%

34
Q

skeletal muscle circualtion - special problems
leg arteries

what is this a major area for? (clinical importance)

A

Leg arteries major areas for atheroma

Ischemia leg pain, ulcers, gangrene

cardio (18 decks)

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