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BRS - Cardio > Microcirculation > Flashcards

Microcirculation Flashcards

1
Q

What is the overall aim of the cardiovascular system?

A

adequate blood flow through capillaries

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2
Q

What is blood flow rate?

A

volume of blood passing through a vessel per unit of time

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3
Q

What is Darcy’s Law / Fluid Circuit?

A 
ΔP = Q x R
ΔP = change in pressure / pressure gradient
Q = flow rate
R = resistance
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4
Q

How is Pressure gradient (ΔP) calculated?

A

Pressure gradient (ΔP) = Pressure (A) - Pressure (B)

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5
Q

What is the result of increasing ΔP?

A

increases flow rate

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6
Q

What is resistance (R)?

A

hindrance to blood flow due to friction between moving fluid + stationary vascular walls

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7
Q

What is the equation for R (resistance)?

A

R = 8Lη/πr^4
• L = vessel length
• η = blood viscosity
• r = vessel radius

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8
Q

What happens to resistance and blood flow rate when vessel radius is halved?

A

increases resistance by 16 times + decreases flow by 16 times

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9
Q

How would increase in blood pressure affect pressure gradient?

A

increases - arriving blood will be higher in pressure

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10
Q

How would increase in blood pressure affect flow rate?

A

increases - higher blood pressure = more flow

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11
Q

How would arteriolar vasoconstriction affect resistance?

A

increases - resistance increases with vasoconstriction

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12
Q

How would arteriolar vasoconstriction affect flow rate?

A

decreases - due to increase in resistance

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13
Q

How do you calculate the flow rate of any organ?

A

F (organ) = ΔP (MAP) / R (organ)

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14
Q

Why is pressure difference important in the arterioles?

A

without pressure difference, blood would not reach tissue capillary beds

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15
Q

What happens to vessel radius when vasoconstriction occurs?

A

decreases

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16
Q

What happens to vessel radius when vasodilation occurs?

A

increases

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17
Q

What happens to resistance when vasoconstriction occurs?

A

increases

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18
Q

What happens to resistance when vasodilation occurs?

A

decreases

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19
Q

What happens to flow rate when vasoconstriction occurs?

A

decreases

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20
Q

What happens to flow rate when vasodilation occurs?

A

increases

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21
Q

What is vascular tone?

A

arteriolar smooth muscle normally displays a state of partial constriction

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22
Q

For what 2 functions are the radii of the arterioles adjusted independently?

A
  • match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)
  • help regulate systemic arterial BP
23
Q

How are the 2 functions of the arterioles regulated?

A
  • local (intrinsic) controls + independent of nervous or endocrine stimulation
  • extrinsic controls which travel via nerves or blood + are usually centrally coordinated
24
Q

How can blood flow meet metabolic needs of tissue chemically?

A

chemically driven by increasing metabolites + O2 usage - causes active hyperaemia

25
Q

What is active hyperaemia?

A

vasodilation of arterioles

26
Q

How can blood flow meet metabolic needs of tissue physically?

A

physically driven by decrease in blood temp + increases stretch (distention) due to increase blood pressure - caused myogenic autoregulation

27
Q

What is myogenic autoregulation?

A

vasoconstriction of arteries

28
Q

What is the equation for cardiac output (which is flow rate) involving BP and resistance?

A

F = ΔP (MAP) / R
Q or F = Cardiac Output
MAP = Blood Pressure
R = Total Peripheral Resistance

29
Q

How is arterial blood pressure regulated neurally?

A

cardiovascular control centre in medulla

30
Q

How is arterial blood pressure regulated hormonally?

A

vasoconstriction caused by:
• vasopressin / ADH secreted by pituitary
• angiotensin II from lungs
• adrenaline/noradrenaline from adrenals

31
Q

What is the purpose of capillary exchange?

A

delivery of metabolic substrates to the cells of the organism

32
Q

What are the general dimensions of a capillary?

A

7µM lumen diameter

1µM cell width

33
Q

What are capillaries specially designed for?

A

Ideally suited to enhance diffusion by Fick’s Law
• minimise the diffusion distance
• maximise the surface area and time for diffusion

34
Q

What tissues have denser capillary networks? Examples?

A

Highly metabolically active tissues:
• Skeletal muscle = 100cm2/g
• Myocardium/Brain = 500cm2/g
• Lung = 3500cm2/g

35
Q

What is special about the capillaries in skeletal muscle?

A

huge capacity but limited flow at rest

36
Q

What are the 3 types of capillaries?

A
  • continuous
  • fenestrated
  • sinusoid / discountinued
37
Q

What are features of continuous capillaries?

A

continuous basement layer + endothelial layer w/ intracellular clefts

38
Q

What are features of fenestrated capillaries?

A

fenestrations in the endothelial layer + continuous basement membrane - allows large molecules to pass through

39
Q

What are features of discontinued capillaries?

A

intracellular gaps + incomplete basement membrane - allows proteins and even blood cells to pass through

40
Q

What is bulk flow?

A

volume of protein-free plasma filters out fo the capillary, mixes with the surrounding interstitial fluid + is reabsorbed

41
Q

How does hydrostatic pressure affect capillaries?

A

pushing force - pushes plasma out of capillary

42
Q

How does oncotic pressure affect capillaries?

A

pulling force - pulls plasma to be reabsorbed into the capillary

43
Q

What was Starling’s theory on capillary fluid movement?

A

hydrostatic pressure of the blood in the capillaries =

osmotic attraction of the blood for the surrounding fluids

44
Q

What causes Ultrafiltration in the capillaries?

A

pressure in capillaries > in interstitial fluid

45
Q

What causes Reabsorption in the capillaries?

A

inward driving pressures > outward pressure across capillary

46
Q

What is more effective; ultrafiltration or reabsorption?

A

ultrafiltration

47
Q

Why is it important that ultrafiltration is more effective?

A

any fluid lost is picked up by lymph vessels + returned to circulation to maintain BP

48
Q

What happens if there is more ultrafiltration than reabsorption?

A

fluid accumulates in IF

49
Q

Why is the lymphatic system important when ultrafiltration > reabsorption?

A

drains the fluid accumulated

50
Q

What happens if the lymphatic system fails?

A

rate of production of fluid > rate of drainage so OEDEMA can occur

51
Q

Where can continuous capillaries be found?

A
  • fat
  • muscle
  • nervous system
52
Q

Where can fenestrated capillaries be found?

A
  • intestinal villi
  • endocrine glands
  • kidney glomeruli
53
Q

Where can discontinuous capillaries be found?

A
  • liver
  • bone marrow
  • spleen

BRS - Cardio (15 decks)

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