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Cardiovascular > Special Circulations > Flashcards

Special Circulations Flashcards

1
Q

Where do the coronary arteries arise from?

A

The left and right coronary arteries arise from the base of the aorta

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2
Q

Where does the venous coronary blood drain into?

A

The coronary sinus into the right atrium

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3
Q

What are the special adaptations of the coronary circulation?

A

High capillary density
High basal blood flow
High oxygen extraction (75% compared to 25% whole body average) under resting conditions
Extra oxygen cannot be supplied by increasing o2 extraction, it can only be supplied by increasing coronary blood flow

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4
Q

What are the intrinsic mechanisms of control of coronary blood flow?

A

A decrease in oxygen conc causes vasodilation of the coronary arteries
Metabolic hyperaemia matches flow to demand
ATP is potent vasodilator

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5
Q

What is metabolic hyperaemia?

A

The increased blood flow that occurs when tissue is active

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6
Q

What are the extrinsic mechanisms to control coronary blood flow?

A

Coronary arterioles are supplied by symp vasoconstrictor nerves BUT this is over-ridden by metabolic hyperaemia as a result of increased HR and SV. Symp stimulation of heart = coronary vasodilatation despite direct vasocontrictor effect
Circulating adrenaline activates B2 aderencoeptors which causes vasodilatation

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7
Q

When is peak left coronary flow?

A

During diastole - a shortening diastole (very fast heart rate) decreases coronary flow

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8
Q

What supplies the brain?

A

The internal carotids and vertebral arteries

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9
Q

How long does it take for ischemia irreversible cell death in the brain?

A

Less than 3 minutes. Grey matter is very sensitive to hypoxia

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10
Q

What is the circle of willis?

A

The basilar (2 vertebral arteries) and carotid arteries anastomose to form circle of willis

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11
Q

What are the 2 types of stoke?

A

Hemorrhagic (bleeding) stoke

Ischemic stroke

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12
Q

What is auto-regulation?

A

The auto-regulation of cerebral blood flow guards against changes in cerebral blood flow if mean arterial blood pressure changes within a range

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13
Q

What occurs if MABP rises?

A

The resistance vessels automatically constrict to limit blood flow

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14
Q

What occurs if MABP falls?

A

The resistance vessels automatically dilate to maintain blood flow

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15
Q

What happens if MABP falls below 60 mmHg or rises about 160 mmHg?

A

Autoregulation fails - if MABP falls below 50 mmHg then it results in confusion, fainting and brain damage can occur quickly

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16
Q

What occurs to cerebral blood flow when carbon dioxide increases?

A

Cerebral vasodilatation

17
Q

What occurs to cerebral blood flow when carbon dioxide decreases?

A

Vasoconstriction, this is why hyperventilation could lead to fainting

18
Q

What is regional hyperaemia?

A

Blood flow increases to active parts of the brain

19
Q

What makes up the skull?

A

80% brain
12% blood
8% cerebrospinal fluid (CSF)

20
Q

What is the normal intercranial pressure?

A

8-13 mmHg

21
Q

What is cerebral perfusion perssure?

A

Mean arterial pressure - ICP

22
Q

What is the effect of an increasing ICP?

A

Can be due to head injury or brain tumour

This decreases CPP and cerebral blood flow

23
Q

What is the blood brain barrier?

A

Cerebral capillaries have very tight intercellular junctions

24
Q

What are cerebral capillaries highly permeable to?

A

Oxygen and carbon dioxide

Glucose can pass through the BB by facilitated diffusion

25
Q

What is the BBB exceptionally impermeable to?

A

Hydrophilic substances such as ions, catecholamines and proteins
This helps to protect the brain neurones from fluctuating levels of ions etc in blood

26
Q

What is the pulmonary arterial BP usually?

A

20-25/6-12 mmHg

27
Q

What is normal pulmonary capillary pressure?

A

8-11 mmHg

28
Q

How does the lungs protect against pulmonary oedema?

A

Absorptive forces excess filtration forces

29
Q

What does hypoxia cause?

A

Vasoconstriction of pulmonary arterioles to help direct blood from poorly ventilated areas of the lung

30
Q

When does the skeletal muscle blood flow increase?

A

During exercise, local hyperaemia overcomes sympathetic vasocontrictor activity
Circulating adrenaline causes vasodilatation
Increased CO during exercise increases skeletal muscle blood flow

31
Q

What is the skeletal muslce pump?

A

Large veins in limbs lie between skeletal muscles and contraction of these muscles aids venous return

32
Q

What does the skeletal muscle pump reduce the chances of?

A

Postural hypotension and fainting

33
Q

What are varicose veins?

A

When blood pools in lower limb veins if the venous valves become imcompetent

Cardiovascular (27 decks)

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