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Cardiovascular > Special ciculations > Flashcards

Special ciculations Flashcards

1
Q

Where do the right and left coronary arteries arise from?

A

The ascending aorta

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2
Q

Where does most of the coronary venous blood drain?

A

Via the coronary sinus into the right atrium

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3
Q

What are the special adaptations of coronary circulation?

A

High capillary density, high basal blood flow and high oxygen extraction

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4
Q

What is the difference between oxygen extraction by the myocytes compared with other cells in the body?

A

Myocytes are able to extract around 75% of oxygen (the whole body average in around 25%)

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5
Q

How does the percentage of extraction affect the way in which oxygen supply is increased to the heart?

A

As the extraction of oxygen cannot be increased any further, the only way to increase oxygen supply to the heart is to increase coronary blood flow

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6
Q

What intrinsic mechanisms increase coronary blood flow?

A

Decreased PO2 causes vasodilation of the coronary arterioles
Metabolic hyperaemia matches flow to demand
Adenosine (from ATP) is a potent vasodilator

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7
Q

What nerves supply the coronary arterioles?

A

The sympathetic vasoconstrictor nerves

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8
Q

What are the sympathetic nerves over-ridden by?

A

Metabolic hyperaemia as a result of increased heart rate and stroke volume

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9
Q

What hormone causes vasodilation and by action on what receptor?

A

Adrenaline activates B2 receptors causing vasodilation

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10
Q

Explain the affect of symoathetic circulation on coronary blood flow

A

Sympathetic stimulation has a vasoconstrictor affect on the coronary arterioles. But it also causes an increased SV and HR, increasing CA which causes vasodilation (increasing coronary blood flow)

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11
Q

During what phase of the cardiac cycle does peak left coronary blood flow happen?

A

Ventricular diastole as during systole the vessels are squeezed

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12
Q

Explain how trachycardia can result in chest pain

A

During trachycardia ventricular diastole is shortened. This means there is less time for coronary blood flow and the oxygen demand of the heart is not met

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13
Q

Why is there not a great difference in cornonary blood flow between systole and diastole on the right side of the heart?

A

They pressure in the right ventricle is lower

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14
Q

What is the Circle of Willis

A 
Part of the cerebral circulation. Internal carotid arteries + vertebral arteries 
Composed of the:
R&L anterior cerebral arteries
Anterior communicating artery
L&R internal carotid artery
L&R posterior cerebral artery 
L&R posterior communicating artery
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15
Q

What is the advantage of the Circle of Willis?

A

Cerebral perfusion should be maintained even if one carotid artery gets obstructed

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16
Q

What causes a stroke?

A

Interruption/cut-off of blood supply to a region of the brain

17
Q

What is the purpose of autoregulation of cerebral blood flow?

A

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

18
Q

What happens to resistance vessels is the MABP rises?

A

They automatically constrict to limit blood flow

19
Q

What happens if MABP falls?

A

The resistance vessels automatically dilate to maintain blood flow

20
Q

What happens is MABP falls below 50mmHg

A

Confusion, fainting and brain damage (if not quiclky corrected)

21
Q

What is the affect of increased PCO2 on cerebral blood flow?

A

Cerebral vasodilation which increases blood flow

22
Q

What is the affect of decreased PCO2 on cerebral blood flow?

A

Causes vasoconstriction

23
Q

What is normal intracranial pressure (ICP)?

A

About 8-13mmHg

24
Q

What is the formula for cerebral perfusion pressure (CPP)?

A

CPP = mean arterial pressure - intracranial pressure (ICP)

25
Q

What is the blood brain barrier?

A

The cerebral capillaries have very tight intercellular junctions

26
Q

What is the blood brain barrier exceptionally impermeable to?

A

Hydrophilic substances such as ions

27
Q

How does pulmonary capillary pressure differ from systemic capillary pressure?

A

Pulmonary capillary pressure is low in comparsion (about 8-11mmHg compared with around 17-25mmHg)

28
Q

What is the affect of hypoxia on pulmonary arterioles?

A

Vasoconstriction

29
Q

What overcomes sympathetic vasocontrictor activity during exercise?

A

Local metabolic hyperaemia

30
Q

What hormone causes vasodilation?

A

Adrenaline (B2 adrenergic receptors)

31
Q

What do skeletal muscles do that aids venous return?

A

Contraction aids venous return

32
Q

What is the name for the condition where blood pools in lower limbs due to incompetent valves?

A

Varicose veins

33
Q

Why do varicose veins not lead to reduction of cardiac output?

A

Varicose veins happen chronically giving time for the body to compensate e.g. through hormones

Cardiovascular (17 decks)

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