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Semester 2 > CVS Session 8 > Flashcards

CVS Session 8 Flashcards

0
Q

What does the bronchial circulation do?

A

Part of systemic circulation that meets metabolic requirements of the lungs

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1
Q

What are the two circulations of the lungs?

A

Bronchial

Pulmonary

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2
Q

What does the pulmonary circulation do?

A

Blood supply to alveoli required for gas exchange

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3
Q

Why just the pulmonary circulation accept the entire cardiac output?

A

It is in series w/ the systemic circulation

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4
Q

What is the maximum cardiac output for a non-athlete?

A

20-25 l per minute

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5
Q

Why does the pulmonary circulation work with low pressure and resistance?

A

High number of branching capillaries giving lots of parallel branches

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6
Q

What are the typical mean arterial, capillary and venous pressures?

A 
Arterial = 12-15 mmHg
Capillary = 9-12 mmHg
Venous = 5 mmHg
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7
Q

How does the amount of smooth muscle in the arterioles in the pulmonary circulation compare to that in the systemic?

A

Relatively little

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8
Q

How is low resistance achieved in the pulmonary circulation?

A

Short, wide vessels
Lots of breaching capillaries
Arterioles with little smooth muscle

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9
Q

What is the combined endothelium and epithelium thickness separating the gas phase from plasma in the pulmonary circulation?

A

~0.3 micrometers

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10
Q

Why does pulmonary oedema tend to accumulate in the lower part of the lung?

A

In orthostatsis gravity causes increased hydrostatic pressure on vessels in this part

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11
Q

What must oxygen and carbon dioxide pass through to reach an erythrocyte?

A

Type 1 pneumocyte –> basement membrane –> endothelial cell –> erythrocyte

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12
Q

Compare the lumen of vessels in the lungs closest to the apex level, closest to the heart level and closest to the base level.

A

Nearest apex = collapse during diastole
Nearest heart = continuously patent
Nearest base = vessels distended

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13
Q

Why is the diastolic pressure in the pulmonary artery higher than in the right atrium?

A

Elastic recoil of the artery

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14
Q

What is needed for efficient oxygenation?

A

Matching of ventilation of alveoli w/their perfusion

Air in/out matched w/bloodflow in same site in lungs

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15
Q

How is the ventilation-perfusion ratio maintained?

A

Divert blood from alveoli that are not well ventilated to those that are

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16
Q

What is the optimal ventilation-perfusion ratio?

A

0.8

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17
Q

What can cause decreased alveoli ventilation?

A

Mucus plug

Fluid build up

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18
Q

What can cause chronic hypoxia?

A

Altitude

Lung disease e.g. emphysema

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19
Q

How does hypoxic pulmonary vasoconstriction lead to right sided heart failure?

A

Alveolar hypoxia –> vasoconstriction –> becomes chronic and widespread –> chronic pulmonary hypertension –> high workload on R ventricle –> R ventricular hypertrophy –> R sided heart failure

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20
Q

What is the effect of exercise in pulmonary blood flow?

A

Increased cardiac output –> small increase in pulmonary arterial pressure –> apical capillaries open –> increased oxygen uptake –> capillary transit time decreases

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21
Q

What does opening of the apical capillaries help to achieve during exercise?

A

Matching of ventilation-perfusion ratio

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22
Q

What range can the capillary transit time lie within?

A

~1 s at rest to ~0.3 s w/out compromising gas exchange

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23
Q

What determines formation of tissue fluid?

A

Starling forces

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24
Q

How do the Starling forces determine tissue fluid formation?

A

Hydrostatic pressure of blood in capillary pushes fluid out

Oncotic pressure/ colloid osmotic pressure draws fluid in to capillaries

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25
Q

What influences capillary hydrostatic pressure more in the systemic circulation?

A

Venous pressure

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26
Q

Will hypertension cause peripheral oedema?

A

No

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27
Q

Why does pulmonary oedema accumulate throughout the lungs when lying down?

A

Capillaries throughout lung become distended

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28
Q

What is the treatment plan for pulmonary oedema?

A

Diuretics to treat symptoms and treat the underlying cause

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29
Q

What does pulmonary oedema impair?

A

Gas exchange

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30
Q

What minimises formation of lung lymph so that it remains at a level that can be dealt with and does not become pulmonary oedema

A

Low capillary pressure

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31
Q

How does the oncotic pressure of tissue fluid in the lungs compare to that in the periphery?

A

Greater than in periphery

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32
Q

How does capillary hydrostatic pressure in lung compare to that in the systemic capillaries?

A

It is lower

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33
Q

What changes in the heart lead to pulmonary oedema?

A

Mitral valve stenosis or left ventricular failure causing left atrial pressure to rise to 20-25 mmHg

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34
Q

How does the plasma oncotic pressure compare in the lungs and systemic circulation?

A

It is equal

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35
Q

How does the percentage of cardiac output received by the brain compare to its mass?

A

Receives ~15% of cardiac output but only account for ~2% of body mass

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36
Q

Why is a secure oxygen supply needed by the brain?

A

Grey matter accounts for ~20% of total body consumption at rest

37
Q

How sensitive are neurones to hypoxia?

A

Very:
Loss of consciousness after a few seconds of cerebral ischaemia
Neuronal death after ~4 mins

38
Q

What is the diffusion distance in the cerebral circulation?

A

< 10 micrometers

39
Q

How does the basal flow rate of the cerebral circulation compare to the average for the rest of the body?

A

10x greater

40
Q

How does oxygen extraction in the cerebral circulation compare to the average for the whole body?

A

35x greater

41
Q

What is the Circle of Willis?

A

Anastomoses b/w basilar and internal carotid arteries

42
Q

What does the Circle of Willis ensure?

A

Interruption of the vertebral/carotid blood supply does not cause lack of blood flow to an area

43
Q

What does the brain stem coordinate?

A

Sympathetic stimulation to cause vasoconstriction to divert blood to brain

44
Q

What do cerebral resistance vessels have in order to respond to changes in transmural pressure?

A

Well developed smooth muscle

45
Q

What is the name given to the use of week developed smooth muscle to maintain cerebral perfusion?

A

Myogenic autoregulation

46
Q

At what pressure does myogenic autoregulation fail causing loss of consciousness?

A

Below 50 mmHg

47
Q

Why is there very little variation on a graph of mean arterial pressure vs cerebral blood flow?

A

Myogenic response

48
Q

What is hypercapnia?

A

Increased p(carbon dioxide)

49
Q

What does hypocapnia stimulate?

A

Vasoconstriction

50
Q

How does panic cause dizziness/fainting?

A

Hyperventilation –> hypocapnia –> vasoconstriction –> lack of cerebral perfusion

51
Q

Why do areas with increased neuronal activity have increased blood flow?

A

They have increased p(carbon dioxide), potassium and adenosine
They have decreased p(oxygen)
Causing vasodilation

52
Q

What is a powerful vasodilator of cerebral arterioles?

A

Adenosine

53
Q

What is Cushing’s reflex?

A

Increase in intracranial pressure impairs blood flow to vasomotor control regions of brain stem –> increased sympathetic vasomotor activity by increased arterial BP and decreased HR from decreased vagal stimulation –> maintains cerebral blood flow

54
Q

What forms the tight blood-brain barrier?

A

Cerebral capillaries w/tight junctions b/w them

55
Q

How can lipid soluble and lipid insoluble molecules move across the blood-brain barrier?

A

Lipid soluble diffuse freely

Lipid insoluble cannot cross barrier

56
Q

Give two examples of lipid insoluble dilutes that cannot cross the blood-brain barrier.

A

Potassium

Catecholamines

57
Q

Give two examples of lipid soluble molecules that freely diffuse through the blood-brain barrier.

A

Oxygen

Carbon dioxide

58
Q

Where do the right and left coronary arteries arise from?

A

Aortic sinuses

59
Q

How much can the work rate of the heart increase when cardiac output needs to be increased?

A

5-fold

60
Q

Why is blood flow into the left coronary arteries usually during diastole?

A

Greater muscle mass causing increased pressure in left side

61
Q

When do the right coronary arteries mainly fill?

A

During systole

62
Q

What facilitates efficient oxygen delivery in the coronary circulation?

A

High capillary density

63
Q

How does capillary density in the coronary circulation compare to that in skeletal muscle?

A

3000 per mm squared in coronary

400 per mm squared in skeletal muscle

64
Q

What maintains a high basal flow in the coronary circulation?

A

Continuous production of NO by coronary endothelium to keep BV relatively dilated

65
Q

What is the relationship between myocardial oxygen demand and coronary blood flow?

A

Linear until very high oxygen demand

66
Q

What molecules cause metabolic hyperaemia to allow vasodilation?

A

Adenosine
High potassium
Low pH

67
Q

How many arterio-arterial anastomoses are there in the coronary circulation?

A

Few

68
Q

What percentage of coronary artery occlusion leads to angina on exercise?

A

80-90%

69
Q

Why does atheroma cause angina on exercise?

A

Diastole time decreases with increasing heart rate so there is less time to fill coronary arteries

70
Q

What two things excluding exercise can cause sympathetic coronary vasoconstriction and angina?

A

Stress

Cold

71
Q

What must the skeletal muscle circulation do during exercise?

A

Increase oxygen and nutrient delivery

Remove metabolites

72
Q

What important role does the skeletal muscle circulation have?

A

Helping regulate TPR

73
Q

How are the resistance vessels in the skeletal muscle circulation innervated?

A

High number of symoathetic vasoconstrictor fibres

74
Q

What maintains blood pressure in the skeletal muscle circulation?

A

Baroreceptor reflex

75
Q

Why is capillary density high in postural muscles?

A

They are continually active

76
Q

Why do skeletal muscle BV have a very high vascular tone to keep the normally quite constricted?

A

Permits up to 20x dilatation

77
Q

Why are only 1/2 the capillaries available perfuse day rest at any one time in the skeletal muscle circulation?

A

Allows for increased recruitment to increase bloodflow and decrease diffusion distance

78
Q

What vasodilator molecules can cause metabolic hyperaemia in the skeletal muscle circulation?

A 
High potassium
Increased osmolarity
High inorganic phosphates 
Adenosine
High hydrogen ion levels
79
Q

How does adrenaline at physiological levels act in the skeletal muscle circulation?

A

Through beta 2 receptors at arterioles causing vasodilation

80
Q

Why does the cutaneous circulation not require much bloodflow?

A

It is not highly metabolically active

81
Q

What is the special role of the cutaneous circulation?

A

Temperature regulation to keep core temp ~37 degrees Celsius

82
Q

What is the main heat dissipating surface regulated by cutaneous blood flow?

A

Skin

83
Q

How does the cutaneous circulation act in shock?

A

Vasoconstricts to maintain BP

84
Q

What are acral areas?

A

Apical areas e.g. fingers, toes, nose, ears

85
Q

What do acral areas have due to their large SA:volume ratio?

A

Artereovenous anastomoses (AVAs)

86
Q

What controls AVAs?

A

Sympathetic vasoconstrictor fibres

87
Q

Do local metabolites act on AVAs?

A

Nope

88
Q

What happens in the cutaneous circulation when the core temperature drops?

A

Increased AVA tone –> decreased blood flow to apical skin

89
Q

What happens in the cutaneous circulation when the core temperature increases?

A

Decreased sympathetic AVA tone –> decreased resistance shunt to venous plexus to bypass capillaries –> vasodilatation in non-apical skin, helped by bradykinin

Semester 2 (45 decks)

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