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Cardio > Special Circulations > Flashcards

Special Circulations Flashcards

1
Q

Describe the basics of coronary circulation

A

The right and left coronary arteries come from the base of the aorta and most arteries drain into the coronary sinus and then into the right atrium.
The heart has a high oxygen demand particularly during exercise

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2
Q

What are the adaptation 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
(so when more oxygen is needed it can’t be done with increased extraction only with increased blood flow)
Coronary Blood Flow is controlled by Intrinsic & Extrinsic Mechanisms

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3
Q

What are the intrinsic mechanisms controlling coronary blood flow?

A

The concentration of O2 falls, so vasodilatation of coronary arterioles
metabolic hyperaemia matches flow to demand
ATP is a potent vasodilator

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4
Q

What are the extrinsic mechanisms controlling coronary blood flow?

A

Supplied by sympathetic vasoconstrictor nerves but these are overridden by metabolic hyperaemia as a result of increased SV and HR
Sympathetic stimulation therefore causes vasodilatation despite its vasoconstrictor effect
Circulating adrenaline activates B2 adrenergic receptors, which cause vasodilatation

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5
Q

When in the cardiac cycle does the coronary blood flow occur?

A

in diastole, so if the HR is too high then there isn’t time for the heart to relax and the coronary blood flow

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6
Q

In systole what happens to the subendocardial vessels from the left coronary artery?

A

They are compressed by the contraction hence coronary circulation is in diastole

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7
Q

What are the different types of stroke?

A

Haemorrhagic stroke blood leaks out of the damaged artery wall
Ischaemic stroke blood flow is blocked off by a clot

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8
Q

What are the adaptations of cerebral circulation?

A

Autoregulation - guards against changes in cerebral blood flow if mean arterial blood pressure changes within a range (~ 60 - 160mmHg)
Sympathetic stimulation has very little effect - cerebral MAP will be pretty constant between 60 and 150
Negligible effect on baroreceptors

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9
Q

Autoregulation of Cerebral blood flow

A

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

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

Autoregulation fails if MABP falls below ~ 60mmHg (cerebral blood flow falls) or rise above ~ 160mmHg (cerebral blood flow rises)

MABP below ~ 50mmHg results in confusion, fainting, and brain damage if not quickly corrected

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10
Q

what are the other external regulations of cerebral blood flow?

A

increased concentration of CO2 causes cerebral vasodilatation, decreased CO2 causes vasoconstriction - hence hyperventilation can cause fainting
it isn’t known how blood flow increases to active parts o the brain possibly due to the K eexchange of the neurones

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11
Q

What is the contents of the Skull?

A

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

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12
Q

What is normal ICP intracranial pressure within the skull?

A

8-13 mm Hg

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13
Q

Cerebral Perfusion Pressure CPP =

A

MAP - ICP

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14
Q

What is the effect on CPP of increasing ICP in the skull?

A

it decreased CPP and cerebral blood flow

some conditions which increase ICP can lead to the failure of the cerebral blood flow auto regulation

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15
Q

What is the blood brain barrier?

A

The cerebral capillaries have very tight intercellular junctions

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16
Q

How does the BBB function?

A

Cerebral capillaries are highly permeable to O2 and CO2
Glucose crosses the BBB by facilitated diffusion using specific carrier molecules to supply the brain’s obligatory requirement for glucose
The BBB is exceptionally impermeable to hydrophilic substances such as ions, catecholamines, proteins etc. which helps to protect the brain neurones from fluctuations of ion concentrations as are in the blood

17
Q

What is pulmonary artery BP typically?

A

20-25/6-12

18
Q

How are the metabolic needs of the airways met?

A

by the bronchial circulation

19
Q

What is the pulmonary resistance?

A

only 10% that of the circulatory system

20
Q

Where does blood enter the pulmonary circulation from?

A

the entire CO enters from the right atrium

21
Q

What is the pulmonary capillary pressure?

A

8-11 mm Hg which is low compared to systemic

22
Q

What protects against pulmonary oedema?

A

absorptive forces> filtration forces

23
Q

What is the effect of hypoxia on the pulmonary arterioles?

A

vasoconstriction - opposite of systemic arterioles

it helps to divert blood from the poorly ventilated areas of the lungs

24
Q

what significance doe the skeletal muscle circulation have on the systemic circulation?

A

the resistance of the skeletal muscle vascular bed has a large impact on blood pressure

25
Q

What causes the skeletal muscle to have a low resting blood flow?

A

Sympathetic vasoconstrictor tone

26
Q

What causes increased muscle blood flow in exercise?

A

Metabolic hyperaemia overcomes sympathetic vasoconstrictor activity
Circulating adrenaline causes vasodilatation (B2 adrenergic receptors)
Plus increased cardiac output during exercise, these could increases skeletal muscle blood flow many folds

27
Q

What supplies the brain with blood?

A

The internal carotids and vertebral arteries, the grey matter in the brain is very sensitive to hypoxia and after a few second there is loss of consciousness and after a few minutes there is irreversible cell damage

28
Q

What are the special adaptations of cerebral circulation?

A

The basilar fored by the 2 vertbral arteries and the carotid arteries anastomose to form the circle of willis
The circle of willis means that cerebral perfusion should be maintained even if one of the carotid arteries gets obstructed as the major cerebral arteries arise from the circle of willis
However an obstruction of a smaller branch of a main artery would deprive a refion of the brain of blood

29
Q

Describe skeletal muscle pump of the venous return

A

The large veins in limbs lie between skeletal muscles, when the muscles contract this aids venous return
1 way venous valve means blood moves forwards towards the heart
This mechanism is important to reduce the rik of postural hypotension and fainting

30
Q

What causes the pooling of blood in veins of the lower limbs?

A

the venous veins becoming incompetent - varicose veins however this doesn’t normally reduce CO because of a chronic compensatory increase in the blood volume

Cardio (36 decks)

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