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BRS 6 Cardio and respiratory > Microcirculation > Flashcards

Microcirculation Flashcards

1
Q

What is the overall aim of the cardiovascular system?

A

Adequate blood flow through the capillaries

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2
Q

What is the definition of the blood flow rate?

A

The volume of blood passing through a vessel per unit of time

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3
Q

What is the equation which describes the change in pressure in a fluid circuit?

A

Change in pressure (between A and B) =
Flow rate (Q) x Resistance (R)

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4
Q

What is the pressure gradient?

A

The difference in pressure between Point A and Point B
(P when blood enters the 1st order arteriole - P when blood enters capillaries)

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5
Q

What affect will increases in flow rate have on the pressure gradient?

A

It will increase the pressure gradient

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6
Q

Flow rate is proportional to…

A

Pressure gradient

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7
Q

Flow rate is inversely proportional to…

A

Resistance

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8
Q

What is the definition of resistance?

A

Hindrance to blood flow due to friction between moving fluid and stationary vascular walls

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9
Q

What is the equation for the resistance experienced in a vessel?

A
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10
Q

What part of the resistance equation is the most variable and can change from minute to minute?

A

The radius of the vessel

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11
Q

Why is having a pressure difference in the organs essential?

A

Otherwise blood would not reach tissue capillary beds

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12
Q

During vasoconstriction, what happens to the pressure gradient, radius, resistance and flow across the vessel?

A

No change to pressure gradient
Radius decreases
Resistance increases
Flow to capillaries decreases

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13
Q

During vasodilation, what happens to the radius, resistance and flow across the vessel?

A

No change to pressure gradient
Radius increases
Resistance decreases
Flow to capillaries increases

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14
Q

What does increasing BP do to pressure gradient, resistance of the vessel and flow to capillaries?

A

Increases pressure gradient
No change to resistance
Increases flow to capillaries

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15
Q

What is meant by vascular tone?

A

The arteriolar smooth muscle normally displays a state of partial constriction

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16
Q

Why is vascular tone important?

A

If the smooth muscle is in a contracted state, then the arteriole wall can contract or dilate - if it was fully dilated at rest, it could only constrict, not dilate further

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17
Q

What does vascular tone affect?

A

Radius of the vessel

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18
Q

What is meant by active hyperaemia?

A

When the blood flow to a specific tissue is matched to its needs and is regulated by chemical changes

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19
Q

What chemical changes can drive active hyperaemia?

A

Increased oxygen usage and increased metabolites

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20
Q

What affect does active hyperaemia have on the arteries?

A

Causes them to vasodilate

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21
Q

What is myogenic autoregulation?

A

When the blood flow to a particular organ is matched by its needs, and is dependent on physical stimuli

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22
Q

What physical stimuli could trigger myogenic autoregulation?

A
  • A drop in blood temperature
  • High blood pressure stretching artery wall
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23
Q

What effect does myogenic autoregulation have on the arteries?

A

causes the arteries to constrict

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24
Q

Through what mechanism are the radii of arteries adjusted after a big meal?

A

Through active hyperaemia in the gut

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25
Q

What is the mean arteriole pressure for 120/80 mmHg?

A

MAP = DBP + 1/3(PP)
MAP = 80 + 1/3(40)
93 mmHg

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26
Q

What happens to the flow of blood through an arteriole following a rapid increase?

A
  • When the flow increases, so does the stretch on the arterioles
  • Therefore, this physical stimuli is detected by the arterioles, which then response through myogenic auto-regulation to bring the flow back to normal
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27
Q

What is laminar blood flow like?

A
  • Velocity of blood is constant at any one point and blood flows in layers
  • Blood flows fastest at the centre of the lumen
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28
Q

What is turbulent blood flow like?

A
  • Blood flows eratically, forming eddys, and is prone to pooling
  • Associated with pathophysiological changes to blood vessel endothelium
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29
Q

What is turbulent blood flow more likely to cause?

A

Activate clotting factors and produce a thrombus

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30
Q

How is turbulent flow used to measure blood pressure?

A

Slow deflation of the cuff causes turbulent flow which can be heard with a stethoscope

31
Q

What is the skeletal muscle arteriolar response to exercise?

A

Active hyperaemia

32
Q

What is the small intestine arteriolar response to exercise?

A

Myogenic vasoconstriction

33
Q

The radii of the arterioles are adjusted independently to accomplish which two functions?

A
  1. Match blood flow to the metabolic needs of the tissue
  2. Regulate systemic arterial blood pressure
34
Q

Through what two mechanisms do the aterioles help regulate arterial blood pressure?

A

Hormonal and Neural

35
Q

How does the neural control of blood vessel radii occur?

A

The cardiovascular control center in the medulla sends signals to vasocontrict to increase blood pressure

36
Q

Which hormones are involved in vasoconstriction?

A

Vasopressin/ADH
Angiotensin II
Adrenaline/noradrenaline

37
Q

Where can the greatest pressure drop in the CVS be observed?

A

From one end of the arteriole to the other

38
Q

What is the equation linking mean arterial pressure, cardiac output and total peripheral resistance?

A

MAP = CO x TPR

39
Q

What is the purpose of capillary exchange?

A

The delivery of metabolic substrates to the cells of the organisms

40
Q

What is the lumen diameter of a capillary?

A

7 micrometers

41
Q

What is the cell width of a capillary?

A

1 micrometer

42
Q

What are capillaries specially designed to do?

A

Minimise the diffusion distance
Maximise surface area and time for diffusion

43
Q

Which tissues have highly dense capillary networks?

A

More metabolically active tissues

44
Q

Which tissue has a large capacity but limited flow at rest?

A

Skeletal muscle

45
Q

Why does the lung have such a dense capillary network?

A

Because of gas exchange which occurs in the lungs

46
Q

What percentage of arterioles are active at rest in skeletal muscle?

A

10%

47
Q

What happens to the arterioles during exercise in sketeal muscle?

A

They vasodilate due to active hyperaemia

48
Q

What is the definition of bulk flow?

A

A volume of protein-free plasma filters out of the capillary, mixes with the surrounding interstitial fluid and is then reabsorbed

49
Q

What is the difference in CO of skeletal muscle when at rest and during exercise?

A

It increases by 5x

50
Q

What are the very small gaps between endothelial cells in continuous capillaries called?

A

H2O filled gap junctions

51
Q

What substances can move across the H2O filled gap junctions?

A

Very small molecules like sodium ions

52
Q

What are fenestrated capillaries?

A

Where you have little gaps/holes in the capillaries

53
Q

Where are fenestrated capillaries found?

A

In the glomerulus, intestinal villi and endocrine glands

54
Q

What are some tissues in which continuous capillaries are found?

A

Fat
Muscle
Nervous System

55
Q

In which capillary can glucose pass through the wall without the need for glucose transporters?

A

Fenestrated capillaries

56
Q

What are discontinuous capillaries?

A

Where there are large caps in the endothelial cells to allow large molecules to pass through

57
Q

Where might you find discontinuous capillaries?

A

In the liver, bone marrow and spleen

58
Q

What type of capillary structure forms the blood brain barrier?

A

Continuous, without water filled gap junction

59
Q

What force pushes plasma out the capillary?

A

Hydrostatic pushing force

60
Q

What force causes plasma to be reabsorbed?

A

Oncotic pulling force

61
Q

What acts as an oncotic force to pull plasma back into the capillaries?

A

Plasma proteins in blood vessels

62
Q

What determines transudation of fluids?

A

Capillary pressure

63
Q

What occurs if pressure inside the capillaries was greater than in the interstitial fluid?

A

Ultrafiltration

64
Q

What occurs if inward driving pressures are greater than outward pressures across the capillaries?

A

Reabsorption

65
Q

What is the significance of the fact that ultra-filtration is more effective than reabsorption?

A

More fluid is lost into the surrounding tissue than is gained - therefore the excess fluid which is lost is picked up by lymphatic vessels and returned to circulation to maintain blood pressure

66
Q

What drives the lymphatic system given there is no central pump?

A

Pressure differences (results in flow)

67
Q

Where do the lymphatics drain into?

A

Into the right lymphatic duct and thoracic duct

68
Q

How much Lymph is drained a day?

A

3L

69
Q

What occurs if the rate of lymph production is greater than the rate of lymph drainage?

A

Oedema – swelling due to interstitial fluid buildup

70
Q

What is elephantiasis?

A
  • A parasitic disease which arises due to the blockage of lymph nodes
  • Thus rate of production exceeds rate of drainage, resulting in oedema
71
Q

What is systemic arterial blood pressure regulated by?

A

Extrinsic controls which travel via nerves or blood

72
Q

How does renin regulate blood pressure?

A
  • Renin from adrenal gland converts angiotensiogen to angiotensin I
  • ACE in the vasculature of lungs and kidneys converts angiotensin I to II
  • Angiotensin II increases blood volume and vasoconstriction, increasing BP
73
Q

How do ADH and adrenaline regulate blood pressure?

A
  • Both increase water reabsorption in the kidney
  • ADH binds to vascular smooth muscle to stimulate vasoconstriction

BRS 6 Cardio and respiratory (26 decks)

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