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CVS * > S8 Special Circulations > Flashcards

S8 Special Circulations Flashcards

1
Q

List 5 of the special circulations.

A
  1. Pulmonary
  2. Coronary
  3. Cerebral
  4. Skeletal
  5. Cutaneous
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2
Q

What are the two circulations in the lungs?

A
  • bronchial circulation

* pulmonary circulation

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3
Q

What is the bronchial circulation?

A
  • part of the systemic circulation

* meets the metabolic requirements of the lungs

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4
Q

What is the pulmonary circulation?

A
  • supplies blood to the alveoli

* required for gas exchange

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5
Q

What must the pulmonary circulation accept the whole of?

A

Whole cardiac output

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6
Q

What is normal CO at rest? What is the maximum CO of a non-athlete?

A
  • 5L/min

* 20-25L/min

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7
Q

Is the pulmonary circulation low or high pressure and resistance?

A
  • low pressure

* low resistance

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8
Q

Why is diastole in the right ventricle the same/lower than diastole in the right atrium?

A

If it was higher than the right atrial diastolic pressure then blood wouldn’t flow as wouldn’t be down a concentration gradient

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9
Q

Why is the pressure in the atria only diastolic pressure?

A

The atria don’t undergo systole like the ventricles do

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10
Q

How is low resistance maintained in the pulmonary circulation?

A
  • short, wide vessels
  • lots of capillaries
  • arterioles with little smooth muscle
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11
Q

What are the mean arterial, capillary and venous pressures in the pulmonary circulation?

A

Arterial - 12-15mmHg
Capillary - 9-12mmHg
Venous - 5mmHg

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12
Q

How is efficient gas exchange promotes in the pulmonary circulation?

A
  • high density of capillaries in alveolar wall - large SA
  • short diffusion distance

Means high oxygen and carbon dioxide transport capacity produced

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13
Q

What is the optimal ventilation-perfusion ratio (V/Q)?

A

0.8

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14
Q

What is needed for efficient oxygenation in terms of V/Q ratio? How is this maintained? When might this happen?

A

Need to match ventilation of alveoli with perfusion of alveoli

Maintained by diverting blood away from alveoli that aren’t well ventilated

Hypoxia

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15
Q

What is hypoxic pulmonary vasoconstriction?

A

Important mechanism in regulating pulmonary vascular tone.
When alveolar hypoxia occurs, vasoconstriction of pulmonary vessels occurs to ensure perfusion matches ventilation (poorly ventilated alveoli are less well perfumed) - to optimise gas exchange

This is the opposite to what happens in systemic circulation

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16
Q

What is a disadvantage of hypoxic vasoconstriction?

A

Can lead to right ventricular heart failure

  • chronic hypoxia can occur at altitude or in diseases like hypoxia
  • the chronic increase in vascular resistance leads to chronic pulmonary hypertension
  • a high afterload on the right ventricle (due to pulmonary hypertension) leads to right ventricular heart failure
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17
Q

What are the low pressure pulmonary vessels strongly influenced by?

A

Gravity

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18
Q

How does gravity effect the pulmonary vessels?

A

In the upright position (orthostasis) there’s increase hydrostatic pressure on the blood vessels in the lower part of the lung

  • at the apex - vessels collapse during diastole
  • at the level of heart - vessels are continuously open
  • at the base - vessels are ‘swollen’/distended
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19
Q

What is the effect of exercise on pulmonary blood flow?

A
  • increases CO
  • there’s a small increase in pulmonary arterial pressure
  • this open apical capillaries (improves the V/Q ratio)
  • there’s increased oxygen uptake by lungs
  • as blood flow increases, capillary transit time decreases (can fall to 0.3s from 1s without compromising gas exchange)
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20
Q

How is tissue fluid formed?

A

Due to Starling forces

  • hydrostatic pressure of blood in capillaries - pushes fluid out
  • oncotic pressure - draws fluid in
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21
Q

In systemic circulation, does arterial or venous pressure influence capillary hydrostatic pressure more?

A

Venous pressure

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22
Q

How is lung lymph formation kept to a minimum?

A

Due to the low capillary pressure

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23
Q

Is oncotic pressure of tissue fluid higher in the lungs or periphery?

A

Lungs

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24
Q

Is capillary hydrostatic pressure higher in the lungs or systemic capillaries?

A

Systemic capillaries

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25
Q

Is plasma oncotic pressure higher in lungs or systemic circulation?

A

Equal

26
Q

What does increased capillary pressure cause?

A

Causes more fluid to filter out and this leads to oedema

27
Q

What prevents pulmonary oedema?

A

Low capillary pressure

28
Q

When can you get pulmonary oedema?

A

When capillary pressure increases e.g. if left atrial pressure rises to 20-25mmHg

  • mitral valve stenosis
  • left ventricular failure
29
Q

What does pulmonary oedema impair? What is it affected by?

A

Impairs gas exchange

Affected by posture (changes in hydrostatic pressure due to gravity) - when upright, oedema forms at base of lungs and when lying down, oedema forms throughout lungs

30
Q

How do you manage/treat pulmonary oedema?

A
  • use diuretics to relieve symptoms

* treat the underlying cause e.g. mitral valve stenosis, left ventricular heart failure

31
Q

How much of the CO does the brain receive?

A

15%

32
Q

How does the cerebral circulation meet the high demand for oxygen?

A
  • high capillary density (large SA and reduced diffusion distance)
  • high basal flow rate
  • high oxygen extraction
33
Q

What are neurones sensitive to, why is a secure oxygen supply to the brain needed?

A

Sensitive to hypoxia

Leads to loss of consciousness within few seconds of cerebral ishcaemia and damage is irreversible after 4 mins

34
Q

How is a secure blood supply to the brain ensured?

A
  • anastomoses between basilar and internal carotid arteries (so even if one blokes, can still get blood to brain)
  • myotonic autoregulation (maintains perfusion during hypotension)
  • metabolic factors control blood flow
  • the brainstem regulates other circulations
35
Q

What is myogenic autoregulation?

A

Maintains cerebral blood flow when blood pressure changes (but fails if BP falls below 50mmHg)

  • if BP increases, vasoconstriction occurs
  • if BP decreases, vasodilation occurs
36
Q

How is cerebral circulation controlled by metabolic regulation?

A

Cerebral vessels are very sensitive to changes in arterial carbon dioxide pressure

  • hypercapnia (increased carbon dioxide) leads to vasodilation
  • hypocapnia (decreased carbon dioxide) leads to vasoconstriction
37
Q

What can panic hyperventilation cause?

A

Hypocapnia and so cerebral vasoconstriction which leads to dizziness and fainting

38
Q

What does regional activity in the brain (neuronal activity) lead to?

A

Increased local blood flow

39
Q

Which aspects/molecules of neuronal activity lead to vasodilation?

A
  • increased carbon dioxide pressure
  • increased K+ concentration
  • increased adenosine - important vasodilator of cerebral arteries
  • decreased oxygen pressure
40
Q

What is Cushing’s Reflex?

A
  • a rigid cranium protects the brain and doesn’t allow for volume expansion
  • so increases in intracranial pressure (cerebral tumour/haemorrhage) impair cerebral blood flow
  • this impaired blood flow to vasomotor control regions of brainstem leads to increased vasomotor activity (bradycardia occurs)
  • arterial BP increases - this helps maintain arterial flow

But need to relieve this pressure, or will die

41
Q

Where do the right and left coronary arteries arise from?

A

Arise from right and left aortic sinuses

42
Q

When does most of the flow to the left coronary artery occur, during systole or diastole? What is a disadvantage of this?

A

Diastole

If HR increases, diastole is shortened, this mean less blood is able to flow to the L coronary artery. Becomes a problem when narrowing of coronary arteries occurs.

43
Q

How is efficient oxygen delivery to heart facilitated?

A
  • high capillary density and they are constantly perfused
  • short diffusion distance
  • a continuous production of NO by the coronary endothelium meant aims a high basal flow - NO causes vasodilation, decreased vascular resistance and inhibition of platelet aggregation
44
Q

How does coronary blood flow increase with myocardial oxygen demand?

A
  • extra oxygen is required if workload is high
  • this is supplied by increased blood flow - vasodilation occurs due to hyperaemia
  • almost linear relationship until v high oxygen demand
45
Q

What are some vasodilators involved in increased blood flow for coronary circulation?

A
  • adenosine
  • increased K+ concentration
  • decreased pH
46
Q

What are coronary arteries prone to due to having few arterio-arterial anastomoses (having many end arteries)?

A

Atheromas

47
Q

What ‘symptom’ do narrowed coronary arteries lead to on exercise? What conditions also lead to sympathetic vasoconstriction and this symptom?

A

Angina

  • due to the increased oxygen demand
  • diastole is reduced as HR increases, but most of blood flow in L coronary artery is during diastole

Stress and cold

48
Q

Sudden obstruction of a coronary artery by a thrombus leads to what?

A

Myocardial infarction

49
Q

When must oxygen and nutrient delivery and removal of metabolites increase in skeletal muscle circulation?

A

During exercise

50
Q

What do skeletal muscle play an important role in regulating?

A

Arterial blood pressure

51
Q

What does capillary density in the skeletal muscle circulation depend on?

A

Depends on muscle type

52
Q

Some vessels in the skeletal muscle circulation are innervated by the sympathetic nervous system. What happens in these vessels, vasoconstriction or vasodilation? What maintains the blood pressure?

A

Vasoconstriction which increases resistance

Baroreceptors

53
Q

What does the high vascular tone of skeletal muscle vessels permit?

A

Permits lots of vasodilation so flow can increased massively in active muscles

54
Q

At rest, how many of the skeletal muscle capillaries are perfused? What is the advantage of this?

A

About half

Means when need perfusion of capillaries due to contraction/metabolic demand/etc the effect is bigger (increased recruitment)

55
Q

What opens to allow more capillaries to be perfused in the skeletal muscle circulation?

A

Precapillary sphincters

56
Q

What agents act as vasodilators?

A
  • increased K+ concentration
  • increased osmolarity
  • inorganic phosphates
  • adenosine
  • increased H+ concentration
57
Q

What does adrenaline act as at arterioles in skeletal muscle? What is the opposite effect?

A

Acts as a vasodilator
* acts through beta-2 adrenoreceptors

Noradrenaline acting on alpha-1 adrenoreceptors causes vasoconstriction

58
Q

What does cutaneous circulation have a role in regulating?

A

Temperature (and blood pressure - via vasoconstriction)

59
Q

What structures does the apical/acral skin have? What is their role in temperature regulation in terms of the cutaneous circulation?

A

Artereovenous anastomoses (AVAs)

They direct blood flow to superficial/deep vessels dependent on whether wanting to lower or increase body temperature

60
Q

What type of control are AVAs under?

A

Neural control - sympathetic vasoconstrictor fibres

61
Q

When are AVAs opened? When are they closed?

A

When there’s an increase in core temperature (decreased sympathetic tone) leads to dilation of AVAs and so diverts blood to superficial veins

Opposite if decreased core temperature - increased sympathetic done so vasocontraction and blood diverted to deep veins

CVS * (17 decks)

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