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BRS Cardio & Respiratory > Microcirculation > Flashcards

Microcirculation Flashcards

1
Q

What are the parts of the microcirculation?

A

1st order arteriole
terminal arteriole
pericytic venule
venule
capillaries
precapillary sphincter
smooth muscle

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2
Q

What is the overall aim of the cardiovascular system?

A

adequate blood flow through the capillaries

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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= deltaP/ resistance

flow rate= pressure gradient/ resistance

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5
Q

What is the pressure gradient?

A
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6
Q

What is resistance?

A

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

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7
Q

How do you calculate resistance?

A

R= 8L/ r^4

l= vessel length
r= vessel radius

it can also be R= (8 x n x L)/ r^4
n= blood viscosity

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8
Q

What happens when you halve the radius?

A

flow decreases x16

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9
Q

What happens to pressure, resistance and flow when blood pressure increases?

A

pressure increases
flow increases

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10
Q

What happens to pressure, resistance and flow when there is arteriolar vasoconstriction?

A

resistance increases
flow decreases

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11
Q

Where does the biggest pressure drop occur?

A

between arterioles

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12
Q

What regulates the pressure within the system?

A

arterioles

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13
Q

How do you calculate flow in an organ?

A
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14
Q

What is special about the pressure gradient in tissues?

A

They are all the same
- only resistance varies
- it determines flow

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15
Q

What happens if there is no pressure difference?

A

Blood would not reach tissue capillary beds

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16
Q

Why is vascular tone important?

A

It allows the arteriole to constrict further or dilate

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17
Q

What happens during relaxation/ vasodilation to radius, resistance and flow?

A

radius increases
resistance decreases
flow increases

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18
Q

What happens during contraction/ vasoconstriction to radius, resistance and flow?

A

radius decreases
resistance increases
flow decreases

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19
Q

What is vascular tone?

A

arteriolar smooth muscle normally displays a state of partial constriction- aka the vascular tone

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20
Q

Radii of arterioles are adjusted independently to accomplish two functions, what are these 2 functions?

A

Function 1: Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)

Function 2: Help regulate systemic arterial blood pressure

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21
Q

How is the “Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)” regulated?

A

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

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22
Q

How is the “Help regulate systemic arterial blood pressure” regulated?

A

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

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23
Q

Explain in more detail the function “Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)”.

A

This function may be chemically driven.
Increases metabolites and O2 usage.
Vasodilation of arterioles.
- skeletal muscles dilate to allow more nutrients etc. to a particular tissue

This is called active hyperaemia (chemically driven change)

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24
Q

Explain in more detail the function “Help regulate systemic arterial blood pressure”.

A

This function may be physically driven.
Decrease blood temperature.
Increase stretch (distension) due to increased BP.
Vasoconstriction of arterioles
- divert blood away

This is called myogenic autoregulation (physically driven change e.g., using an ice pack)

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25
Q

What happens to resistance, flow, perfusion with autoregulation and no autoregulation?

A
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26
Q

How do you calculate cardiac output?

A

blood pressure (MAP)/ Total peripheral resistance (TPR)

Q= MAP/ TPR

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27
Q

How does the neural aspect of the arteriole function “help regulate arterial blood pressure” work?

A

Neural
Cardiovascular control centre in the medulla
Leads to vasoconstriction
Leading to decreased blood flow in specific organs (you want this acutely as this can become dangerous)

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28
Q

How does the hormonal aspect of the arteriole function “help regulate arterial blood pressure” work?

A

vasopressin/ ADH
Angiotensin II
Adrenaline/ noradrenaline

they all lead to vasoconstriction

29
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]

30
Q

What is the diameter of a capillary?

A

7 micrometers lumen diameter

31
Q

What is the width of capillary wall?

A

1 micrometer width

32
Q

How are capillaries designed to promote?

A

Ideally suited to enhance Fick’s law

Minimise the diffusion distance
Maximise the surface area and time for diffusion

33
Q

Why is capillary density important?

A

highly metabolically active tissues have denser capillary networks
skeletal muscle= 100cm2/g
myocardium/ brain= 500cm2/g
lung= 3500cm2/g

34
Q

What is a special feature of skeletal muscle?

A

skeletal muscle has a huge capacity, but limited flow at rest
- at rest most arterioles are closed off, doesn’t function normally

35
Q

How does cardiac output from rest and exercise differ considering the different organs involved?

A
36
Q

What do continuous capillaries have?

A

H2O filled gap junction

37
Q

Where can you find fenestrated capillaries?

A

e.g., in the kidney

38
Q

What are fenestrated capillaries?

A

larger gaps between endothelial cells

39
Q

Where can you find discontinuous capillaries?

A

bone marrow
- exit route for WBC

liver
- large metabolic capacity

spleen, lymph nodes, and endocrine glands

40
Q

What are discontinuous capillaries?

A

even larger gaps and pores

41
Q

What are the 3 types of capillaries?

A
42
Q

What type of capillary is the blood brain barrier?

A

Continuous
Really small junctions
tight control of what leaves the BBB and enters the brain

43
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

44
Q

What are the 2 forces acting on capillaries?

A

Hydrostatic “pushing” force
Oncotic “pulling” force

45
Q

What is starling’s hypothesis about fluid movement?

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.”

46
Q

What is the fluid movement for ultrafiltration?

A

pressure inside the capillary> pressure in the IF

47
Q

What is the fluid movement during reabsorption?

A

inward driving pressures> outward pressures across the capillary

48
Q

Does hydrostatic pressure change across the capillary?

A

Yes, it decreases

49
Q

what happens to oncotic pressure across the capillary?

A

It stays the same

50
Q

What is oncotic pressure?

A

form of osmotic pressure induced by the proteins, notably albumin, in a blood vessel’s plasma that causes a pull on fluid back into the capillary.

51
Q

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

A

There is a net loss
THE ROLE OF THE LYMPHATIC SYSTEM

52
Q

What are the parts of the lymphatic system?

A

Blood capillary
Arteriole
Lymphatic endothelium
Anchoring filament
Interstitial fluid
Openings
Tissue cells
Lymphatic capillary

53
Q

What is the lymphatic system specialised to do relating to direction of flow?

A

designed to ensure fluid can only enter the lymphatic system and not leave

54
Q

What are the different lymph nodes and ducts you need to know?

A

Right lymphatic duct
Entrance of thoracic duct into subclavian vein
Thoracic duct

55
Q

Describe the lymphatic system.

A

There is no pump to induce flow
Drainage-right lymphatic duct- thoracic duct
Right and left subclavian veins

56
Q

How many litres of lymph a day?

A

3L

57
Q

How does lymph move around the body?

A

Negative pressure of lungs and contraction of skeletal muscle

58
Q

How does an oedema form with lymph?

A

rate of production> rate of drainage
(too much fluid leaving capillaries staying in the space)

59
Q

What causes elephantiasis?

A

parasitic blockage of lymph nodes

or sometimes rate of production> rate of drainage

60
Q

What is the pressure entering and leaving arterioles?

A

93 mmHg entering

37 mmHg leaving

61
Q

Why are capillaries so important?

A

critical exchange vessels for nutrients, signals and waste

62
Q

How would you describe capillaries?

A

narrow, thin, highly branched

63
Q

What is density in capillaries proportional to?

A

metabolic activity

64
Q

How would you describe lymph vessels?

A

blind ended, single layered, contains large permeable water-filled one way channels

65
Q

When is excess interstitial fluid drained?

A

constantly

66
Q

What directs lymph flow?

A

skeletal and respiratory pumps (vessels coalesce to lower neck

67
Q

What are lymph nodes for?

A

defence mechanism

68
Q

What does lymphatic failure lead to?

A

oedema

BRS Cardio & Respiratory (28 decks)

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