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Y1 - Cardiovascular > Physiology: Special Circulations (Coronary, Cerebral, Pulmonary, MSK) > Flashcards

Physiology: Special Circulations (Coronary, Cerebral, Pulmonary, MSK) Flashcards

1
Q

List the special adaptations of the coronary circulation that allow it to adequately supply the heart

A
  • high capillary density
  • high basal flow rate
  • high oxygen extraction from blood
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2
Q

Describe why the only way to to increase heart oxygenation is to increase coronary blood flow

(i.e. why can’t O2 extraction increase)

A

Because at resting conditions oxygen extraction is very high (~75%) (normal tissues have ~25%)

This means O2 extraction can’t be increases further, thus can only be increased by increasing flow

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3
Q

List the intrinsic factors that increase coronary blood flow

A

PO2 decrease –> vasodilatation

Metabolic hyperaemia (due to metabolites) –> matches flow with tissue demand

Adenosine (from ATP) –> vasodilatation

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4
Q

Define metabolic hyperaemia

A

The increased blood flow that occurs when tissue is active

Due to:

  • Increased cardiac output
  • Metabolites
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5
Q

List the extrinsic factors that control coronary blood flow

A

Sympathetic stimulation of vessels –> Vasoconstriction

Metabolic hyperaemia (due to increased heart rate and stroke volume)

Adrenaline (in blood) –> Vasodilatation

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6
Q

Give examples of metabolites that contribute to metabolic hyperaemia

A
  • CO2
  • K+
  • H+
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7
Q

Define functional sympatholysis

A

Opposition to sympathetic stimulation

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8
Q

Is there a period of peak flow in the right coronary artery?

Why?

A

No, not really

During systole the subendocardial vessels in the right coronary artery are not compressed much

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9
Q

Is there a period of peak flow in the left coronary artery?

When?

Why?

A

Yes, during diastole

Due to:

During systole the subendocardial vessels in the left coronary artery are compressed

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10
Q

Describe why tachycardia decreases coronary blood flow

A 
Tachycardia
-->
Diastole duration decreases
-->
Flow decreases

(more important in the left coronary artery)

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11
Q

Why does the brain need a very secure supply of oxygen?

A

Grey matter is very sensitive to hypoxia

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12
Q

List the special adaptations of the cerebral circulation that allow it to adequately supply the brain

A
  • The Circle of Willis
  • Autoregulation of cerebral blood flow
  • Regional hyperaemia
  • Response to PCO2 levels
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13
Q

Describe the structure of the circle of Willis

What is its function?

A

A ring formed by the anastomosis of the Basilar artery and carotid arteries

It provides a collateral circulation for major cerebral arteries

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14
Q

Describe the autoregulation of cerebral blood flow

Give the autoregulatory response to an increase/decrease in MAP

A

Autoregulation of cerebral blood flow guards against changes in MAP

It ensures constant cerebral blood flow

MAP increase = Vasoconstriction
MAP decrease = Vasodilation

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15
Q

Describe the participation of the cerebral vasculature in the baroreceptor reflex

Why is this?

A

Negligible

To maintain a constant cerebral blood flow

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16
Q

Describe the effect of sympathetic stimulation on overall cerebral blood flow

A

Direct sympathetic stimulation has very little effect in overall cerebral blood flow

Minor vasoconstrictor effects

17
Q

Give the MAP range in which the autoregulation of cerebral blood flow works

A

60 - 160 mmHg

18
Q

Describe the effects of an increase/decrease in local PCO2 on cerebral arterioles

A

Pco2 increase:

  • cerebral vasodilatation
  • prevents CO2 build up

Pco2 decrease:
- cerebral vasoconstriction

This is why hyperventilation could lead to fainting

19
Q

Define cerebral regional hyperaemia

Give a possible mechanism for its action

A

Blood flow increases to active parts of the brain

Mechanism unknown:
- Due to rise in extracellular [K+] as a result of K+ efflux from repetitively active neurons

20
Q

What is the normal intracranial pressure (ICP)?

A

8 - 13 mmHg

21
Q

What 2 factors determine the cerebral perfusion pressure?

Give the equation linking them

A

MAP and ICP

Cerebral Perfusion Pressure (CPP) = MAP - ICP

22
Q

Describe the effect of an increased intracranial pressure (e.g. due to trauma)

A

Decreases cerebral perfusion pressure
–>
Cerebral perfusion decreases

23
Q

What is the blood brain barrier?

A

The barrier between cerebral capillaries and brain tissue

Due to cerebral capillaries’ very tight intercellular junctions

24
Q

What can cross the blood brain barrier?

A
  • oxygen
  • carbon dioxide
  • glucose (facilitated diffusion)
25
Q

What cannot cross the blood brain barrier?

A

Hydrophilic substances:

  • ions
  • catecholamines
  • proteins
26
Q

How much of the cardiac output flows through the pulmonary circulation?

A

The entire CO

27
Q

What circulation meets the metabolic needs of the pulmonary tissue?

A

Systemic bronchial circulation

28
Q

What is the average pressure in the pulmonary artery?

Describe the average pressure in the pulmonary capillaries

A

Low
(20/6 - 25/12 mmHg)

Low
(8-11 mmHg)

29
Q

Describe the special adaptation of the pulmonary circulation:

A
  • Low capillary Bp
  • Absorptive forces exceed filtration forces (protects against pulmonary oedema)
  • Hypoxia causes vasoconstriction of pulmonary arterioles
30
Q

Why does hypoxia causes vasoconstriction of pulmonary arterioles?

A

Diverts blood from poorly ventilated areas of lung to better ventilated areas

This increases efficiency

31
Q

What factors increase blood flow to skeletal muscle during exercise?

A
  • regional metabolic hyperaemia
  • Adrenaline in blood
  • CO increases, increasing blood flow
32
Q

On what receptor does adrenaline act?

A

β2 adrenergic receptors

33
Q

Describe the mechanism of the skeletal muscle pump

A

Skeletal muscle contraction aids in venous return from deep veins

34
Q

Describe varicose veins

A

Blood pools in lower limb veins if venous valves become incompetent

They don’t lead to a drop in CO as it develops slowly

Y1 - Cardiovascular (19 decks)

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