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Cardiovascular system > Lecture 14- Special Circulation > Flashcards

Lecture 14- Special Circulation Flashcards

1
Q

name 6 special circulations

A

pulmonary

cerebral

coronary

skeletal

cutaneous

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2
Q

blood supply to the lungs

A
  • bronchial circulation
  • pulmonary circulation
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3
Q

Bronchial circulation

A

Part of systemic circulation

Meets the metabolic requirements of the lungs (e.g. provides oxygen)

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4
Q

Pulmonary circulation

A

Blood supply to alveoli

Required for gas exchange

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5
Q

pulmonary circulation must be carefully adapted to accept the

A

entire cardiac output

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6
Q

at rest CO is

A

5 L/min

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7
Q

maximum CO

A

20-25 L/min

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8
Q

adaptations of pulmonary ciruclation

A
  • Works at low pressure and low resistance
    • Mean arterial pressure 12-15 mmHg
    • Mean capillary pressure 9-12 mmHg
    • Mean venous pressure 5mmHg
  • Short, wide vessels
  • Lots of capillary (many parallel elements)
  • Arterioles have relatively little smooth muscle
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9
Q
A
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10
Q

adaptions of the alveoli to promote efficient gas exchange

A
  • High density of capillaries in alveolar wall – large capillary surface area
  • Short diffusion distance
    • Thin layer of tissue separating gas phase from plasma
    • 0.3um
  • Large surface area and short diffusion distance produce high O2 and CO2 transport capacity
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11
Q

perfusion ration (V/Q ratio)

A

For efficient oxygenation- need to match ventilation of alveoli with perfusion of alveoli

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12
Q

optimal V/Q ratio

A

0.8

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13
Q

to maintain the optimum V/Q ratio what must occur

A

diverting blood from alveoli which are not well ventilated

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14
Q

Hypoxic pulmonary vasoconstriction

A
  • Ensures optimal ventilation/ perfusion ration
  • Hypoxic pulmonary vasoconstriction is the most important mechanism regulating pulmonary vascular tone
  • Alveolar hypoxia results in vasoconstriction of pulmonary vessels
  • Ensure perfusion matches ventilation
    • Poorly ventilated alveoli are less well perfused
  • Ensure optimal gas exchange
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15
Q

However… Chronic hypoxic vasoconstriction can cause

A

right ventricular failure

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16
Q

how can Chronic hypoxic vasoconstriction cause right ventricular failure

A
  • Chronic increase in vascular resistanceà chronic pulmonary hypertension
  • Increased afterload (the resistance the heart has to pump against)à right ventricular heart failure (hypertrophy due to having to pump harder)
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17
Q

when does chronic hypoxic vasoconstriction occur

A

Can occur at altitude or as a consequence of lung disease such as emphysema

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18
Q

Low pressure pulmonary vessels are strongly influenced by

A

gravity

In upright position there is greater hydrostatic pressure on vessels in the lower part of the lungs

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19
Q

when patients lie down

A

more vessels across the whole lung become distended

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20
Q

Effect of exercise on pulmonary blood flow

A
  • Increased CO
  • Small increase in pulmonary arterial pressure
  • Opens apical capillaries
  • Increased oxygen uptake by lungs
  • As blood flow increases capillary transit time is reduced
  • At rest transit time is 1s
  • Can fall to 0.3s without compromising gas exchange
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21
Q

formation of tissue fluid is determined by

A

starling forces

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22
Q

starling forces

A

Hydrostatic pressure of blood within the capillary forces fluid out of the capillary

Oncotic pressure is the pressure exerted by large molecules such as plasma proteins (albumin) àdraws fluid into the capillary

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23
Q

in systemic circulation capillary hydrostatic pressur is more influenced by

A

venous pressure

(hypertension does not usually result in peripehral oedema)

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24
Q

what minimised the formation of lung lymph

A

low capillary pressure (lower than systemic capillaries) and oncotic pressure of tissue fluid (oncotic pressure is higher in the lungs)

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25
Q

increased capillary pressure causes

A

more fluid to filter out- oedema

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26
Q

Low capillary pressure

A

prevents pulmonary oedema —> pulmonary pressure usually low (only a small amount of fluid leaves)

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27
Q

what can cause pulmonary oedema (caused by capillary pressure increase)

A

if left atrial pressure rises to 20-25 mmHg

Mitral valve stenosis

Left ventricular failure

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28
Q

pulmonary oedmea forms mainly ……. when upright

A

at the base

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29
Q

pulmonary oedema forms throughout the lungs when

A

lying down

30
Q

why is pulmonary oedema dangerous

A

impairs gas exchange

31
Q

what can be used to help relieve the symtoms of pulmonary oedema

A

diuretic

32
Q

the brain has a high demand for

A

oxygen

33
Q

how much of CO does the brain receive

A

15%

34
Q

O2 consumption by grey matter accounts for …….of total body consumption at rest

A

20%

35
Q

why must the brain have a secure supply of oxygen

A
  • Neurones sensitive to hypoxia
  • Loss of consciousness within a few second of cerebral ischaemia
  • Irreversible damage to neurone in 4 minutes

E.g. interruption to blood supply e.g. stroke causes neuronal death

36
Q

how does cerebral ciruclation meet the high demand for O2

A
  • High capillary density
    • Large SA for gas exchange
    • Reduced diffusion distance
  • High basal flow rate- X10 average for whole body
  • High O2 extraction (35% above average)
37
Q

structurally how is a secure blood supply ensured

A

Anastomoses between basilar and internal carotid arteries

38
Q

functionally how is secure blood supply to the brain ensured?

A

Myogenic autoregulation maintains perfusion during hypotension

Metabolic factors control blood flow

Brainstem regulates other circulations

39
Q

regional activity produces local increases in blood flow

A

Neurones with increases neurones activity have increase blood flow

40
Q

Signals of increased neuronal activity

A
  • Increased pCO2
  • increased [K+]
  • Increased adenosine (strongest vasodilator of cerebral arterioles)

Strong vasodilators

  • decrease in oxygen
41
Q

myogenic autoregulation- increased blood pressre

A

vasoconstriction

42
Q

myogenic autoregulation- decreased blood pressure

A

vasodilation

43
Q

Cerebral resistance vessels have a well developed myogenic response to changes in transmural pressure.

A

Maintains cerebral blood flow when BP changes

Will fail below 50 mmHg

44
Q

panic hyperventilation can lead to

A

hypocapnia and cerberal vasoconstirction leading to dizziness or fainting

45
Q

Cushing’s reflex

A

Rigid cranium protects the brain- but does not allow for volume expansion.

  • Increases in intracranial pressure impairs cerebral blood flow (e.g. cerebral tumour or haemorrhage)
  • Impaired blood flow to vasomotor control regions of the brainstem increase sympathetic vasomotor activity
    • Increases arterial BP
    • Maintains cerebral blood flow
46
Q

cushings reflex ensures

A

The Cushing reflex helps save braintissues during periods of poor perfusion.

47
Q
A
48
Q

coronary ciruclation must

A
  • Must deliver oxygen at a high basal rate
  • Must meet increased demand à can work at a rate increased 5-fold
49
Q

where do the right and left coronary arteries arise from

A

right and left aortic sinuses

50
Q

when does flow in the left coronary artery mainly occur

A

during diastole

51
Q

Adaptations in coronary circulation

A
  • High capillary density (3000/mm2, compared to 400/mm2 in skeletal muscle) facilitates efficient oxygen delivery
  • Diffusion distance <9um
  • Continuous production of NO by coronary endothelium maintains a high basal flow
52
Q

coronary blood flow increases with

A

myocardial oxygen demand

53
Q

Vasodilation of coronary arterys causes

A

metabolic hyperaemia- excess of blood in the vessels supplying an organ

54
Q

vasodilaotrs of coronary circulation

A

adenosine

potassium

decreased pH

55
Q

Coronary arteries are functional

A

end arteries

56
Q

functional end arteries

A

an artery that is the only supply of oxygenated blood to a portion of tissues. Arteries that don’t anastomose with neighbours

57
Q

where there are few anastosomes

A

prone to atheroma

  • Narrowed coronary arteries leads to angina on exercise (increase O2 demand)
    • Blood flow mostly during diastole
    • Diastole is reduced as heart rate increases (due to exercise)
58
Q

what can cause coronary vasoconstirction and angina

A

stress and angina

59
Q

Sudden obstruction by thrombus causes

A

myocardial infarction

60
Q

during exerise skeletal muscle requires

A

increased O2 and nutrient delivery and removal of emtabolites

61
Q

skeletal muscl plays an importnant role in helping to

A

regulate arterial blood pressure

62
Q

Adaptations of skeletal muscle circulation

A
  • Capillary density depends on muscle type
    • Postural muscles- in constant use- have higher capillary density
  • Very high vascular tone
    • Permits lots of dilatation
    • Flow can increase >20 times in active muscle
    • At rest only half capillaries are perfused at any one time–> allows for increased recruitment
  • Opening of precapillary sphincters allows more capillaries to be perfused
    • Increased blood flow and reduces diffusion distance
63
Q

increased flow causes metabolic hyperaemia in skelteal muscle ciruclation. Which agents act as vasodilators

A
  • Increased potassium
  • Increased osmolarity
  • Inorganic phosphates
  • Adenosine
  • Increased hydrogen
  • Adrenaline
    • Through B2 receptors
    • Vasoconstrictor response via NA on alpha1
64
Q

what is cutaenous circulation

A

The circulation and blood supply of the skin

65
Q

cutaneous circulation has a special role in

A

temp regulation (core temp 36.5 to 37.5 degrees)

  • skin is main dissipating surface
66
Q

cutaneous circulation also plays a role in

A

Vasoconstriction in cutaneous circulation maintains BP

67
Q

Apical skin has specialised structures called

A

arteriovenous anastomoses (AVA)

68
Q

arteriovenous anastomoses (AVA)

A

AVAs are low-resistance connections between the small arteries and small veins that supply and drain the skin. These allow the shunt of blood directly into the venous plexus of the skin, without it passing through capillaries. Since AVAs contain no capillary section, they are not involved in transport of nutrients to/from the tissues, but instead play a major role in temperature regulation.

69
Q

AVAs are not regulated by

A

Not regulated by local metabolised

70
Q

AVAs are under

A

Under neural sympathetic control (vasoconstrictor fibres)

Reduced vasomotor drive to AVA allows them to dilate- diverts blood to veins near surface

71
Q

Decrease core temp increases sympathetic tone in AVA

A

Decrease in blood flow to apical skin

72
Q

increased core temp

A

opens AVAS

Cardiovascular system (30 decks)

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