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CVS > Coronary, cerebral and cutaneous circulation > Flashcards

Coronary, cerebral and cutaneous circulation Flashcards

1
Q

What is a-vO2 difference?

A

The amount of O2 a tissue extracts to meet its metabolic demands.
A large a-vO2 shows a high demand

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2
Q

How does coronary circulation maintain a secure O2 supply?

A

Alters local flow via FUNCTIONAL HYPERAEMIA. It can increase by 4-5 times when CO increases due to the CORONARY RESERVE.

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3
Q

What is the a-vO2 difference in coronary circulation?

A

Very large at 120ml.L extracting almost maximum at rest as it cannot withstand anaerobic conditions.

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4
Q

As the coronary tissue extracts almost max O2 at rest, how is an increase in O2 demand met?

A

Increase flow

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5
Q

How does coronary flow vary throughout the cardiac cycle?

A

The flow to muscle is intermittent as in order for it to flow Pa>Pv AND Pin>Pout. A pressure difference must be present to keep the vessel open.

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6
Q

What is the flow to coronary vessels on the left side of the heart?

A

Flow to LV ceases during SYSTOLE as Pout>Pin. The vessels are compressed from the high ventricular pressure.
Most flow occurs during DIASTOLE.
Aortic pressure determines flow, with max flow being reached early in diastole allow for a shortened diastole at high HR.

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7
Q

What happens to the left coronary vessels during systole?

A

The contracting myocytes collapse the vessels, forcing blood backwards towards the aorta = EXTRAVASCULAR COMPRESSION.

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8
Q

How do coronary vessels penetrate the myocardium?

A

At right angles

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9
Q

What is the flow to the coronary vessels on the right side of the heart?

A

The RV produces a lower pressure during systole, as they only need to open the pulmonary valve, so the flow is CONTINUOUS throughout the cycle. Pin>Pout. Most of the flow is received during SYSTOLE.

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10
Q

What happens during metabolic hyperaemia of the coronary muscle?

A

Adenosine is released from metabolising muscle to DILATE the arterioles for increased flow. PGs, low O2, NO and K can all cause vasodilation.
Also have myogenic autoregulation between 60-180mmHg.

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11
Q

What is the sympathetic influence on coronary vessels?

A

Overruled by local control and hyperaemia.

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12
Q

What results from a reduced flow through the coronary arteries?

A

Angina e.g. in exercise

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13
Q

How does cerebral circulation ensure a secure O2 supply?

A

Via myogenic autoregulation and local flow can be altered according to brain activity via functional hyperaemia.

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14
Q

What results from a low cerebral perfusion pressure?

A

Loss of consciousness as cannot tolerate anaerobic conditions. Supply lost for >4min causes neuronal damage.

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15
Q

How is the cerebral circulation structurally adapted to ensure perfusion is maintained if an artery becomes blocked?

A

Circle of Willis.
Short arterioles and dense capillary network at high vascular resistance with blood arriving from the ICA or vertebral A.

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16
Q

Why are the coronary capillaries not leaky?

A

BBB limits the passage due to its tight junctions. Lipophilic pass unaided but AA require protein transport and ions need channels. Needs to maintain a constant environment to protect the neurons.

17
Q

What are the adaptations of the cerebral circulation?

A
  • High basal flow = 15% of CO
  • Peripheral vasoconstriction maintains pressure by shunting from other organs
  • myogenic autoregulation within 60-170mmHg.
  • Vessels are responsive to hypercapnia to cause vasodilation. Less responsive to PO2 with only severe hypoxia causing dilation
  • Functional hyperaemia
  • Little ANS control with sympathetic only contributing to 20-30% increased resistance and little baroreceptor effect.
18
Q

What is myogenic autoregulation?

A

A change in BP is met by a change in resistance to maintain the flow.

19
Q

How does systemic hypoxia present?

A

Hypoxia evokes hyperventilation so becomes masked by HYPOcapnic vasoconstriction.

20
Q

What causes raised ICP and what results from it?

A

Bleeding, oedema, tumour = collapses veins and reduces CPP.

21
Q

CPP =

A

Mean ABP - ICP

22
Q

What causes postural syncope?

A

Due to an impairment in the baroreceptor reflex or autonomic activity. Linked to age

23
Q

What causes cerebral ischaemia?

A

Ischaemic or haemorrhagic stroke

24
Q

What can vasodilation in cerebral circulation result in?

A

Headaches or migraines

25
Q

What is the purpose of cutaneous circulation?

A

To regulate body temperature, respond to trauma and from a protective barrier.

26
Q

How does blood flow through the cutaneous circulation? Does it have any special adaptations?

A

Receives 10% of CO, despite low metabolic demand. High resistance flow.
Microvascular network of AV shunts to bypass capillaries for heat loss and shunting when other organs require flow.

27
Q

What controls cutaneous circulation?

A

Sympathetic control through alpha receptors.

28
Q

What happens with a raised body temperature?

A

Decreased sympathetic activation to alpha1 = dilation of av shunts = increased flow to venous plexus = heat loss

29
Q

Where are av anastomoses found?

A

Hands, feet, ears, nose, lips

30
Q

What can enhance the vasodilation effeect in cutaneous circulation?

A

Bradykinin - released due to sweat

31
Q

What effect does heat have on the circulation overall?

A

Dilation reduces vascular resistance to reduce ABP and trigger baroreceptors for increased HR and CO. Heat to SAN increased HR to prevent low TPR.

32
Q

What happens with a reduced body temperature?

A

Reduced temperature stimulates alpha receptors for cold induced vasoconstriction.

33
Q

What happens after a prolonged exposure to cold? How is it achieved?

A

PARADOXICAL VASODILATION - Allows flow to return to tissues to pervent injury. The alpha receptors are paralysed.

34
Q

Why does the cold cause redness?

A

Due to increased affinity of O2 in Hb

35
Q

What is the countercurrent exchange in cutaneous circulation?

A

Allows radiation of heat from warm arterioles to cold venuoles flowing in the opposite direction as it returns from the extremities. Extremities are <13 degrees cooler than the trunk.

36
Q

What is Raynaud’s syndrome?

A

An overreactive vessel response to cold/emotional stimuli causing vasoconstriction and ischaemic attacks. hands turn white, then blue due to cyanosis and then red. It causes numbness, pain and burning as the blood flow returns.

37
Q

What is the triple response of cutaneous trauma?

A

White reaction - blanching due to mechanical stimuli
Red reaction - local vasodilation due to histamine
Flare - Wider intense vasodilation causing local oedema

CVS (15 decks)

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