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Cardiovascular > Special Circulations > Flashcards

Special Circulations Flashcards

1
Q

What is the definition of coronary heart disease?

A

Where there is an area of cardiac muscle deprived of blood supply if coronary vessel is blocked.

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2
Q

What are the 3 special adaptations of the coronary circulation?

A

High capillary density, high basal flow, high oxygen extraction (around 75% compared to 25% whole body average) under resting conditions.

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3
Q

What does the high oxygen extraction of the coronary circulation mean when extra oxygen is required?

A

It cannot be supplied by further increasing O2 extraction but can only be supplied by increasing coronary blood flow.

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4
Q

What are the intrinsic mechanisms which control coronary blood flow?

A
  1. Decrease in PO2 causes coronary arteriole vasodilation.
  2. Metabolic hyperaemia (increased blood flow when tissue is active) matches flow to demand.
  3. Adenosine is a potent vasodilator.
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5
Q

Why do coronary arterioles supplied by sympathetic vasocontrictor nerves dilate as a result of increased heart rate and stroke volume?

A

The sympathetic stimulation is over-ridden by metabolic hyperaemia.

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6
Q

What is the term used to describe coronary vasodilation despite sympathetic stimulation of the heart?

A

Functional sympatholysis.

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7
Q

What are the adrenergic receptors in the coronary vessels and what effect does adrenaline binding have on the vessels?

A

B2, causes vasodilation.

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8
Q

Why does most of the coronary blood flow and myocardial perfusion occur in diastole?

A

Because the subendocardial vessels are not compressed.

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9
Q

What effect will shortening diastole e.g. very fast heart rate have on the coronary blood flow?

A

Will decrease coronary flow.

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10
Q

Why does the brain need a secure supply of oxygen?

A

Grey matter is very sensitive to hypoxia.

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11
Q

What arteries anastomose to form the circle of Willis?

A

Basilar (formed by two vertebral arteries) and carotid.

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12
Q

What is the advantage of the circle of Willis?

A

Means cerebral perfusion should be maintained even if one carotid artery gets obstructed.

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13
Q

Does the autonomic nervous system affect cerebral blood flow much?

A

No.

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14
Q

Through what ranges can autoregulation of cerebral blood flow be maintained?

A

60-160mmHg.

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15
Q

What change in cerebral blood flow occurs when the PCO2 changes?

A

Increase in PCO2 - vasodilation. Decrease in PCO2 - vasoconstriction (why hyperventilation could lead to fainting).

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16
Q

What is regional hyperaemia and what is thought to cause it?

A

Blood flow increases to active parts of the brain. May be due to rise in extracellular potassium concentration as a result of potassium efflux from repetitively active neurones.

17
Q

What is the value of normal intracranial pressure (ICP)?

A

8-13mmHg.

18
Q

How can you calculate cerebral perfusion pressure (CPP)?

A

MAP-ICP

19
Q

What effect does increasing intra-cranial pressure have on cerebral blood flow?

A

It decreases CPP so decreases cerebral blood flow (conditions which increase ICP lead to failure of autoregulation of cerebral blood flow).

20
Q

What forms the blood brain barrier?

A

The very tight intercellular junctions in cerebral capillaries.

21
Q

What gases are cerebral capillaries highly permeable to?

A

Oxygen and carbon dioxide.

22
Q

How does glucose cross the blood brain barrier?

A

Facilitated diffusion using specific glucose carrier molecules.

23
Q

What is the BBB exceptionally impermeable to and why is this a good thing?

A

Hydrophilic substances such as ions, catecholamines and proteins. Helps protect neurones from fluctuating levels of ions in the blood.

24
Q

What is the typical pulmonary artery blood pressure?

A

(20-25)/(6-12)mmHg.

25
Q

What causes the absorptive forces in the pulmonary capillaries to exceed the filtration forces and why is this good?

A

Pulmonary capillary pressure is low (8-11mmHg). Protects against pulmonary oedema.

26
Q

What effect does hypoxia have on pulmonary arterioles and what is the benefit of this?

A

Causes vasocontriction (opposite in systemic), helps divert blood from poorly ventilated areas of lung.

27
Q

What causes resting blood flow to be low in skeletal muscle circulation?

A

Sympathetic vasoconstrictor tone.

28
Q

How does skeletal muscle blood flow increase during exercise?

A

Local metabolic hyperaemia overcomes sympathetic tone. Circulating adrenaline binds to B2 receptors causing vasodilation (same as coronary). Increase in CO during exercise.

29
Q

What condition occurs if venous valves become incompetent?

A

Varicose veins (due to blood pooling in lower limb veins).

30
Q

Why don’t varicose veins lead to a reduction of cardiac output?

A

Chronic compensatory increase in blood volume.

Cardiovascular (32 decks)

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