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1. Cardiovascular > Special Circulations > Flashcards

Special Circulations Flashcards

1
Q

What is the route of Coronary Circulation?

A

Most coronary venous blood drains via coronary sinus into the right atrium

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2
Q

What are the special adaptations of the Coronary Circulation?

A

Can only be supplied by increasing coronary blood flow
High Capillary Density
High Basal Blood Flow
High Oxygen Extraction

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3
Q

How is Coronary blood flow controlled?

A

Extrinsic and Intrinsic Mechanisms

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4
Q

What are the intrinsic mechanisms to control coronary blood flow?

A

decreased Po2 causes vasodilatation of the coronary arterioles
Metabolic hyperaemia matches flow to demand
Adenosine (from ATP) is a potent vasodilator

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5
Q

What are the extrinsic mechanisms to control coronary blood flow?

A

Coronary arterioles supplied by sympathetic vasoconstrictor nerves but are over-ridden by metabolic hyperaemia as a result of increased heart rate and stroke volume
So sympathetic stimulation of the heart results in coronary vasodilatation despite direct vasoconstrictor effect (functional sympatholysis)
Circulating adrenaline activates 2 adrenergic receptors, which cause vasodilatation

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6
Q

When does most of the coronary blood flow occur and why?

A

diastole - when the subendocardial vessels from the left coronary artery are not compressed

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7
Q

How is the Cerebral system supplied?

A

Brain is supplied by internal carotids and vertebral arteries

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8
Q

What happens to gray matter after 3 minutes without oxygen?

A

consciousness lost after few seconds of ischaemia

irreversible cell damage

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9
Q

Where do major cerebral arteries arise from?

A

Circle of Willis

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10
Q

What two arteries astamose to form the Circle of Willis?

A

BASILAR (formed by two vertebral arteries)

CAROTID arteries

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11
Q

Why is Cerebral Circulation Autoregulated?

A

guards against changes in cerebral blood flow if mean arterial blood pressure changes within a range (~ 60 - 160mmHg)

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12
Q

How does autoregulation work?

A

If MABP rises, resistance vessels automatically constrict to limit blood flow
If MABP falls, resistance vessels automatically dilate to maintain blood flow

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13
Q

When would autroregulation fail? and what is the result?

A

MABP below 60mmHg (cerebral blood flow falls)

MABP rise above 160mmHg (cerebral blood flow rises)

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14
Q

What does MABP below 50 result in?

A

confusion, fainting, and brain damage

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15
Q

What is a normal intercranial pressure in the skull?

A

8-13 mm Hg

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16
Q

What does Cerebral Perfusion Pressure =?

A

Mean Arterial Pressure (MAP) - Intercranial Pressure (ICP)

17
Q

What can cause an increase in intercranial pressure?

A

brain tumour, head injury

18
Q

What does increased ICP lead to?

A

decreased cerebral perfusion pressure and cerebral blood flow

19
Q

What is the blood brain barrier?

A

tight intercellular junctions that the cerebral capillaries have

20
Q

How does glucose cross the blood brain barrier?

A

facilitated diffusion using specific carrier molecules

21
Q

What is the blood brain barrier impermeable to?

And why is this advantageous?

A
  1. hydrophilic substances such as ions, catecholamines, proteins
  2. helps protect brain neurones from fluctuating levels of ions etc in blood
22
Q

Describe the Pulmonary Circulation

A

Entire cardiac output flows from right ventricle into pulmonary circulation

23
Q

What is a normal pulmonary artery BP?

A

20-25/6-16 mmHg

24
Q

What are the special adaptations of the pulmonary circulation?

A

Pulmonary capillary pressure is low (~ 8-11 mmHg) compared to systemic capillary pressure (~ 17-25 mmHg)
Absorptive forces exceed filtration forces - protects against pulmonary oedema

Hypoxia causes vasoconstriction of pulmonary arterioles which helps divert blood from poorly ventilated areas of lung

25
Q

Describe the Skeletal muscle circulation

A

Resistance of skeletal muscle vascular bed has large impact on blood pressure
Resting blood flow is low because of sympathetic vasoconstrictor tone

26
Q

How does skeletal muscle blood flow change during exercise?

A

increases

27
Q

How does skeletal muscle blood flow increase during exercise?

A
  • local Metabolic hyperaemia overcomes sympathetic vasoconstrictor activity
  • Circulating adrenaline causes vasodilatation (B2 adrenergic receptors)
  • increased cardiac output during exercise, this could increase skeletal muscle blood flow many folds
28
Q

What does contraction of muscles aid?

A

Venous return

29
Q

What does the skeletal muscle pump reduce?

A

the chance for postural hypotension & fainting

30
Q

What is the skeletal muscle pump?

A

One-way venous valves allow blood to move forward towards the heart

31
Q

What are Varicose Veins?

A

Blood pools in lower limb veins if venous valves become incompetent

1. Cardiovascular (30 decks)

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