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Cardiology > Microcirculation > Flashcards

Microcirculation Flashcards

1
Q

What comprise microcirculatory system?

A

Arterioles
Capillaries
Venules

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2
Q

What is the overall aim of CVS?

A

Adequate blood flow through the capillaries

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3
Q

What is the blood flow rate?

A

Volume of blood passing through a vessel per unit time

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4
Q

What determine blood flow rate?

A

Flow rate = Pressure gradient/Resistance

Darcy’s law

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5
Q

What is pressure gradient equal to?

A

Difference in pressure between Pressure A (arteriole) and Pressure B (capillary)

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6
Q

Define resistance

A

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

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7
Q

What affects resistance

A

Vessel length
Vessel radius
Blood viscosity

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8
Q

Which factor affecting resistance changes dynamically?

A

Vessel radius

The only factor that changes resistance dynamically

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9
Q

What happens to pressure, resistance and flow rate when blood pressure increase?

A

delta P- increases
R- unchanged
F- increases

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10
Q

What happens to pressure, resistance and flow rate during arteriolar vasoconstriction?

A

delta P- unchanged
R- increases
F- decreases

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11
Q

What has the biggest influence on resistance?

A 
Arterioles
Lots of muscle
Lots of capacity to constrict and dilate
Biggest change in pressure seen between two ends of an arteriole (50mmHg drop)
Greatest resistance in the CVS
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12
Q

What is blood flow to different tissues dependent on?

A

Resistance
Pressure gradient is the same across all tissues
Resistance determines how much blood flow each tissue gets

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13
Q

How can arterioles control resistance?

A

Vasoconstriction:

  • radius increases
  • resistance increases
  • flow decreases

Vasodilation:

  • relaxation
  • radius increases
  • resistance decreases
  • flow increases
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14
Q

Why are arterioles partially constricted at rest?

A

Aterirole smooth muscle normally displays a state of partial constriction- this is called vascular tone

At rest arterioles must be partially constricted to allow them to both dilate and further constrict

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15
Q

What are the two functions of adjusting arteriole radii?

A

Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)

Help regulate systemic arterial blood pressure

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16
Q

How is matching blood flow regulated?

A

Regulated by local (intrinsic) controls and independent of nervous or endocrine stimulation

17
Q

How is relating systemic arterial blood pressure regulated?

A

Regulated by extrinsic controls which travel via nerves or blood and are usually centrally coordinated

18
Q

What is matching blood flow chemically driven by?

A

Chemically driven by:
Increase in metabolites
Increase in O2 usage
Will lead to vasodilation

19
Q

What is the increase in blood flow in response to increase demand called?

A

Active hyperaemia

20
Q

What is matching blood flow physically driven by?

A

Decrease in blood temperature
Increase in stretch (distension) due to increased blood pressure
Leads to vasoconstriction

21
Q

What is the decrease in blood flow in response to factors?

A

Myogenic autoregulation

22
Q

What would occur skeletal muscle and small intestine arterioles in response to exercise?

A

SM- active hyperaemia

SI- myogenic vasoconstriction

23
Q

How do arterioles help regulate arterial blood pressure? (Neural)

A

Cardiovascular control centre in the medulla
Causes vasoconstriction
Decreases blood flow the specific organs

24
Q

How do arterioles help regulate arterial blood pressure? (Hormonal)

A

Arginine vasopressin (ADH)
Angiotensin II
Adrenaline/Noradrenaline

Stimulate vasoconstriction

25
Q

What is the purpose of capillary exchange?

A

delivery of metabolic substrates to the cells of the organism [which is the ultimate function of the CVS]

26
Q

Why is capillary density important?

A

Depends on how metabolically active the tissue is
Ideally suited to enhance diffusion: Fick’s law
Specially designed to minimise diffusion distance
Maximise the SA and time for diffusion

27
Q

How does capillary density vary within the body?

A

Highly metabolically active tissues have denser capillary networks
Skeletal muscle = 100cm2/g
Myocardium/brain = 500cm2/g
Lung = 3500cm2/g
(not related to metabolic activity bur rather gas exchange)

28
Q

Why is capillary structure important?

A

For exchange
Thin walls
Small H2O filled gap junctions
Proteins embedded in capillary

29
Q

What are fenestrations?

A

Circular holes that allow for slightly larger molecules to pass through the capillary

30
Q

What is discontinuous capillary?

A

Need to allow for much larger substances between the blood and tissue
e.g. in bone marrow when white cells need to be transported
and liver

31
Q

What is bulk flow?

A

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

32
Q

What draws fluid back into he blood?

A

Oncotic pulling force

protein gradient related

33
Q

What pushes fluid out into tissues?

A

Hydrostatic pushing force

34
Q

What did Starling hypothesise?

A

“…there must be a balance between the hydrostatic pressure of the blood in the capillaries and the osmotic attraction of the blood for the surrounding fluids. “

” …and whereas capillary pressure determines transudation, the osmotic pressure of the proteins of the serum determines absorption.”

35
Q

When would ultrafiltration take place?

A

If pressure inside the capillary > in the IF

36
Q

When would reabsorption take place?

A

If inward driving pressures > outward pressures across the capillary

37
Q

What is the significance of the fact that ultrafiltration is more effective than reabsorption?

A

Overall net loss

Role of the lymphatic system is to return fluid back to the blood

Cardiology (16 decks)

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