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Z YEAR 1 BRS cardiology > Microcirculation > Flashcards

Microcirculation Flashcards

1
Q

What is the overall aim of the CVS?

A

Adequate blood flow

through the capillaries

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2
Q

What is the microcirculation?

A
  • Arterioles
  • Capillaries
  • Venules
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3
Q

What is blood flow rate?

A

Volume of blood passing through a vessel per unit time

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4
Q

How do you calculate flow rate?

A

Q (flow rate) = Pressure gradient / Resistance

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5
Q

What is pressure gradient?

A

Pressure gradient (DP) = Pressure A – Pressure B

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6
Q

What will an increase in pressure gradient do?

A

Increase flow rate

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7
Q

What is resistance?

A

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

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8
Q

What impacts resistance?

A
  1. Vessel length
  2. Vessel radius (changes)
  3. Blood viscosity
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9
Q

What happens in increased blood pressure?

A

Pressure gradient: increase
R:
F: increase

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10
Q

What happen in arteriolar vasoconstriction?

A

Pressure gradient:
R: increase
F: decrease

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11
Q

When is the biggest pressure difference?

A

One end of arteriole to another

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12
Q

How do you calculate flow rate for an organ?

A

Forgan = pressure gradient (MAP) / Rorgan

-Without this pressure difference blood would not reach tissue capillary beds

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13
Q

What happens in vaso contraction?

A

r: decrease
R: increase
F: decrease

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14
Q

What happens in vasodilation?

A

r: increase
R: derease
F: increase
-

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15
Q

Why is vascular tone important?

A
  • Arteriolar smooth muscle normally displays a state of partial constriction (this is vascular tone)
  • If you need capacity to both dilate and contract (can contract further or dilate)
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16
Q

How many ways can radii of arterioles adjust independently?

A

Radii of arterioles are adjusted independently to accomplish two functions

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17
Q

What is the first function? How is this regulated?

A
  1. Function 1: Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)
  2. Regulated by local (intrinsic) controls and independent of nervous or endocrine stimulation
18
Q

What is the second function? How is this regulated?

A
  1. Function 2: Help regulate systemic arterial blood pressure
    2 Regulated by extrinsic controls which travel via nerves or blood and are usually centrally coordinated
19
Q

How does the arterioles match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs) chemically?

A
  • If more active: function may be chemically driven
  • increase metabolites + O2 usage
  • Therefore vasodilation of arterioles (tissue dilates)
  • Called active hyperaemia
20
Q

How does the arterioles match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs) physically?

A
  • function may be physically driven
    1. Decrease blood temp
    2. Increase stretch (distension) due to increase BP
  • Therefore vasoconstriction of arterioles
  • Called myogenic auto regulation
21
Q

What happens if BP increases?

A
  • Flow to nay tissue bed increases
  • As blood flow increases it stretches
  • If tissue realises it doesn’t need this responds and contracts
  • To ensure that blood doesn’t increase to every tissue
22
Q

In exercise what happens?

A
  1. Skeletal muscle arterials go to active hyperaemia

2. Small intestine arterioles go toward myogenic vasoconstriction

23
Q

Generate and equation for flow across the whole circulation and rearrange to generate a BP equation?

A

Cardiac output (Q) = Blood pressure (MAP) / totally peripheral resistance (TPR)

24
Q

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

A
  1. Cardiovascular control centre in medulla (e.g. loss of blood) for vasoconstriction (to maintain BP)
    - This would decrease blood flow to specific organs as vasoconstriction decrease flow
    - Brain is no1 💓
25
Q

What hormonal controls cause vasoconstriction?

A
  1. Vasopressin/ADH
  2. Angiotensin II
  3. Adrenalin/noradrenaline
26
Q

What is the purpose of capillary exchange?

A

The purpose of capillary exchange is the delivery of metabolic substrates to the cells of the organism [which is the ultimate function of the CVS]

27
Q

What is the structure of capillaries?

A
  • 7 muM lumen diameter
  • 1 muM cell width
  • Highly branched network
  • Thin wall
  • No tissue to far away
28
Q

Why is capillary density important?

A
  • Different in different tissue beds
  • Ideally suited to enhance diffusion Fick’s law
  • Specially designed to:
    1. Minimise the diffusion distance
    2. Maximise the surface area and time for diffusion
29
Q

What do different tissues need capillary density?

A
  1. Highly metabolically active tissues have denser capillary networks
    - Skeletal muscle = 100cm2/g
    - Myocardium/brain = 500cm2/g (metabolically)
    - Lung = 3500cm2/g (for efficiency)
    - Skeletal muscle has a huge capacity, but limited flow at rest
30
Q

What are continuous capillaries?

A
  • one cell thick
  • very small H2O filled gap junction
  • Diffuse across cell or gap
  • Most common
31
Q

What is fenestrated capillaries?

A
  • Lots of fenestrae
  • Larger holes around 80nM
  • In glomerulus
32
Q

What is discontinuous capillaries?

A
  • Larger and less common

- Bone marrow and in liver

33
Q

What type of capillary is in blood brain barrier?

A

-Continuous for protection and continue with no gap junctions so difficult to leave and enter -not lipid soluble won’t get in

34
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
  • Bulk Flow
35
Q

What are the different forces with blood flow?

A
  • Hydrostatic ‘pushing’ force (forced out of capillary)

- Oncotic ‘pulling force’ (to return blood, more protein in blood), draws fluid back in

36
Q

What is Starlings hypothesis?

A

Starling’s hypothesis (1896)
“…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.”

37
Q

What happens

If pressure inside the capillary > in the IF?

A

Ultrafiltration

38
Q

What happens If inward driving pressures > outward pressures across the capillary?

A

Reabsorption

39
Q

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

A

Overall net loss, role of lymphatic system (return fluid back)

40
Q

What is the lymphatic system?

A
  • Present in all tissues and are blind-ended, single-layered and contain large permeable water-filled one-way channels
  • Drain excess interstitial fluid constantly – skeletal and respiratory pumps direct lymph flow – vessels coalesce to lower neck
  • Nodes = defence mechanism, lymphatic failure -> oedema

Z YEAR 1 BRS cardiology (10 decks)

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