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Cardiology > Special Circulations: coronary; cerebral; pulmonary; skeletal > Flashcards

Special Circulations: coronary; cerebral; pulmonary; skeletal Flashcards

1
Q

Where do the left/right coronary arteries arise from?

A
  • base of the aorta
  • at the aortic sinuses
  • in the aortic (semilunar) valve
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2
Q

Where does most coronary venous blood drain into?

A
  • coronary sinus (into right atrium)
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3
Q

Where does coronary heart disease commonly occur?

A
  • left side (anterior surface) of heart
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4
Q

Name 3 special adaptations of coronary circulation

A
  • high capillary density (exchange of O2/nutrients helps oxygenate cardiac muscle)
  • high basal blood flow
  • high O2 extraction
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5
Q

Describe O2 extraction by the heart

A
  • heart extracts ~75% of O2 from blood (compared to 25% whole body average) under resting conditions
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6
Q

Can the heart increase O2 extraction (to increase oxygenation of cardiac muscle)?

A
  • no (heart already extracts so much O2, cannot manage any more!)
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7
Q

How can oxygenation of the heart be improved (if we can’t extract more oxygen from the blood?)

A
  • increase coronary blood flow
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8
Q

Name the intrinsic mechanism of controlling coronary blood flow

A
  • decreased PO2 (hypoxia): vasodilation of CA
  • metabolic hyperaemia (increased blood flow): matches flow to O2 demand
  • adenosine (from ATP breakdown): potent vasodilator
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9
Q

Name the extrinsic mechanisms of controlling coronary blood flow

A
  • sympathetic vasoconstrictor nerves supply coronary arterioles (THIS IS NOT WANTED)
  • metabolic hyperaemia overcomes vasoconstriction
  • this occurs as a result of increasing HR + SV (>CO)
  • circulating adrenaline is released from adrenal cortex
  • adrenaline activates beta 2 adrenoceptors
  • this causes vascular smooth muscle dilation (similar to sympathetic effect on bronchial smooth muscle)
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10
Q

What is the sympathetic process of coronary vasodilaton called?

A
  • function sympatholysis
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11
Q

Does sympathetic stimulation on alpha adrenoceptors improve coronary blood flow?

A
  • no (vasoconstrictor = reduces blood flow)
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12
Q

What causes metabolic hyperaemia?

A
  • increased cardiac work (SV/HR)
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13
Q

What metabolites are released as a result of metabolic hyperaemia?

A
  • K+
  • Co2
  • H+
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14
Q

When does peak LEFT coronary blood flow occur?

A
  • during diastole
  • left CA is situated near left ventricle
  • systole = high pressure in LV (+ left CA)
    coronary blood flow falls during systole
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15
Q

Describe peak RIGHT coronary blood flow

A
  • right CA situated close to RV
  • systole: RV squeezed
  • lower pressure in RV than LV
  • blood flow to right CA not reduced as much
  • blood flow between systole + diastole remains similar
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16
Q

What is the effect of shortening diastole on coronary blood flow?

A
  • reduced diastole
  • reduced coronary blood flow
  • ischaemia
  • chest pain
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17
Q

What can cause reduced diastole?

A
  • tachycardia
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18
Q

What supplies arterial blood to the brain?

A
  • internal carotids

- vertebral arteries

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19
Q

Describe the effect of hypoxia on grey matter in the brain

A
  • grey matter = very sensitive to hypoxia
  • unconsciousness after a few seconds of ischaema
  • irreversible necrosis (cell damage) within ~3mins
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20
Q

Give an alternative (latin) name for the circle of Willis

A

Circulus Arteriosus Cerebri

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21
Q

What is the circle of Wilis?

A
  • anastomotic system of arteries that lies at the base of the brain
  • formed when the internal carotid artery enters the cranial cavity (bilaterally) and divides into the anterior cerebral + middle cerebral arteries
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22
Q

Describe the branching of the anterior cerebral artery

A
  • anterior cerebral arteries are united by anterior communicating arteries
  • these connections form the anterior half of the circle of Willis
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23
Q

Describe the posterior branches of the circle of Willis

A
  • posteriorly, the BASILAR artery is formed by the left/right vertebral arteries
  • basilar arteries branch into a left/right posterior cerebral artery
  • posterior cerebral arteries complete the circle of Willis by joining the internal carotid system anteriorly via the posterior communicating attires
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24
Q

How is cerebral perfusion maintained?

A
  • via function of circle of Willis

- even if the carotids are obstructed, perfusion can be maintained via the other cerebral arteries

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25
Q

How is ischaemia caused in the brain?

A
  • obstruction of one of the smaller branch arteries in the circle of Willis
26
Q

Name the 2 main types of stroke

A
  • ischaemic

- haemorrhagic

27
Q

What can cause an ischaemic stroke?

A
  • atherosclerotic obstruction
  • thrombus
  • embolus
    ATRIAL FIB
28
Q

What is auto regulation?

A
  • guard against cerebral blood flow when changes in MAP occur (within the range 60-160 mm Hg)
29
Q

What is the effect of the following on cerebral blood flow? a) sympathetic stimulation b) baro receptors

A

a) little overall effect

b) negligible (don’t want cerebral vasoconstriction/dilation in response to baroreceptor stretch)

30
Q

When does auto regulation fail?

A
  • if MAP < 60 mmHg or >160 mm Hg
31
Q

What happens in cerebral blood flow if MAP rises?

A
  • resistance vessels CONSTRICT

- limits cerebral blood flow

32
Q

What happens in cerebral blood flow if MAP falls?

A
  • resistance vessels DILATE

- maintains cerebral blood flow

33
Q

Symptoms of a MAP <50 mmHg?

A
  • fainting
  • confusion
  • brain damage
34
Q

How can we calculate MAP?

A
  • diastole + 1/3 x (systole-diastole)
35
Q

What are the following effects on cerebral blood flow? a) increasing CO2 b) decreasing CO2

A

a) cerebral vasodilation

b) cerebral vasoconstriction

36
Q

Why does hyperventilation lead to fainting?

A
  • blowing off CO2
  • decreased CO2
  • cerebral vasoconstriction
  • decreased blood flow
37
Q

What is regional hyperaemia?

A
  • blood flow increases to active parts of the brain

- due to K+ efflux from repetitively active neurones (?)

38
Q

What % of the skull is?

a) brain
b) blood
c) cerebro-spinal fluid (CSF)

A

a) 80%
b) 12%
c) 8%

39
Q

What is the normal intracranial pressure? (ICP)

A

8-13 mm Hg

40
Q

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

A

CPP = MAP - ICP

41
Q

What is the effect of increased ICP?

A
  • decreased cerebral perfusion pressure
  • opposes cerebral blood flow
  • failure of auto regulation
42
Q

What conditions increase ICP?

A
  • head injury

- brain tumour

43
Q

Describe the blood-brain barrier?

A
  • cerebral capillaries have very tight intracellular junctions allowing selective movement of substances across
44
Q

What can pass the BBB?

A
  • O2; CO2

- glucose (by facilitated diffusion using carrier molecules) (brain has obligatory glucose requirement)

45
Q

What can’t pass BBB?

A
  • hydrophilic substances
    e. g. ions/catecholamines/proteins
  • helps to protect brain from fluctuating levels of ions in blood
46
Q

Where does the entires cardiac output flow into from the right ventricle?

A
  • pulmonary circulation
47
Q

How are the metabolic needs of the airway met?

A
  • via systemic bronchial circulation (bronchial arteries = branch of thoracic aorta)
48
Q

What % of total systemic circulation is pulmonary circulation?

A
  • about 10%
49
Q

What is the typical pulmonary artery BP?

A

20-25 (systole)

6-12 (diastole)

50
Q

What is the pulmonary capillary resistance (in mmHg)? How does this differ from systemic capillary resistance?

A
  • pulmonary capillary resistance is low (8-11 mm Hg)

- systemic capillary resistance is around 17-25 mm Hg

51
Q

What adaptation of pulmonary circulation protects you from pulmonary oedema?

A
  • absorptive forces exceed filtration forces
52
Q

What is the effect of hypoxia on a) pulmonary arterioles b) systemic arterioles?

A

a) vasoconstriction

b) vasodilation

53
Q

Why is the effect of hypoxia opposite for pulmonary and systemic circulation?

A
  • vasoconstriction of pulmonary arterioles helps to divert blood from poorly ventilated areas of lung
  • diverts blood from poorly oxygenated area to area that is in higher demand of oxygen
  • occurs to maintain V/Q balance
54
Q

What % of total body mass is skeletal muscle?

A
  • 40%
55
Q

How does skeletal muscle impact blood pressure?

A
  • resistance of skeletal muscle vascular bed has large impact on BP
56
Q

What maintains resting blood flow?

A
  • sympathetic vasoconstrictor tone
57
Q

Describe the changes that occur in skeletal circulation during exercise

A
  • local metabolic hyperaemia overcomes sympathetic vasoconstrictor activity
  • circulation adrenaline acts on beta 2 adrenoceptors to cause vasodilation
  • increased cardiac output = increased skeletal blood flow during exercise
58
Q

Where is the skeletal muscle pump situated?

A
  • in large limbs
59
Q

What does the skeletal muscle pump do?

A
  • contraction of muscle aids venous return

- one way venous valves allow blood to move forward toward the heart

60
Q

What does the skeletal muscle pump protect against?

A
  • postural hypotension + fainting
61
Q

What is a blood pool?

A
  • collections of blood in the lower limb veins if venous valves become incompetent
  • these venous blood pools are called varicose veins
62
Q

Do varicose veins lead to a reduction in CO? (reduced venous return; decreased SV; decreased CO?)

A
  • no
  • causes a compensatory increase in blood volume
  • maintains normal CO

Cardiology (6 decks)

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