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BRS 6: Cardiovascular And Respiratory Medicine > 6.6: Microcirculation > Flashcards

6.6: Microcirculation Flashcards

1
Q

Calculation for pressure gradient to work out blood flow to capillary

A

(P) = pressure A - pressure B
(Pressure A - arteriolar pressure)
(Pressure B - capillary network pressure)

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2
Q

Overall aim of cardiovascular system is

A

Adequate blood flow through capillaries

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3
Q

Blood flow rate is

A

Volume of blood passing through a vessel per unit time

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4
Q

Darcys law calculation and calculating flow rate

A

( P = Q x R )
Q = P/R (flow rate = pressure / resistance)

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5
Q

What does an Increase in pressure gradient do to the flow rate

A

Increases flow rate

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6
Q

Resistance (R) is

A

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

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7
Q

3 factors affecting resistance

A

Vessel length
Vessel radius
Blood viscosity

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8
Q

Impact of vessel radius on resistance

A

Vessel radius can change rapidly, therefore has the greatest impact on resistance
Halving radius decreases flow x16

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9
Q

What happens to pressure gradient as blood pressure increases

A

Pressure increases

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10
Q

What happens to pressure during arteriolar vasoconstriction

A

Remains the same

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11
Q

What happens to resistance during increased blood pressure

A

Stays the same

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12
Q

What happens to resistance during arteriolar vasoconstriction

A

Resistance increases

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13
Q

What happens to flow as blood pressure increases

A

Flow increases

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14
Q

What happens to flow during arteriolar vasoconstriction

A

Flow decreases

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15
Q

Calculation of blood flow or any organ

A

Blood flow = change in pressure/ resistance against entire organ

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16
Q

What would happen without a pressure difference to the blood

A

Blood would not reach tissue capillary beds

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17
Q

How does vasoconstriction affect radius, resistance and flow

A

Radius decreases
Resistance increases
Flow decreases

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18
Q

How does vasodilation affect radius, resistance and flow

A

Radius increases
Resistance decreases
Flow increases

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19
Q

Why is it important for smooth muscle to display a state of partial constriction (vascular tone)?

A

Vascular tone allows for dilation and constriction to regulate blood flow

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20
Q

Why are the radii of arterioles adjusted independently

A

To accomplish two functions :
Match blood flow to metabolic needs of specific tissues
Help regulate systemic arterial blood pressure

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21
Q

What is matching blood flow to metabolic needs regulated by

A

Local (intrinsic) controls, and independent of nervous or endocrine stimulation

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22
Q

What is regulating systemic arterial blood pressure controlled by

A

Extrinsic controls which travel via nerves or blood and are usually centrally coordinated

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23
Q

What is active hyperaemia

A

Tissue starts working harder:
Increased metabolites and O2 usage
Vasodilation of arterioles
-chemical

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24
Q

What is myogenic autoregulation

A

E.g twisting ankle
Aim is to induce vasoconstriction
Decrease blood temperature
Increase stretch (distension) due to increased blood pressure
Decrease blood flow

25
Q

What is stretch distension due to increased blood pressure

A

Pressure gradient across every micro circulation increases
In tissues which are not being used- autoregulation occurs as increase in arteriole pressure is detected: arterioles constrict to regulate blood flow
Allowing blood flow to heart, brain, lungs

26
Q

Skeletal muscle arterioles during exercise undergo

A

Active hyperaemia

27
Q

Small intestines arterioles during excersise undergo

A

Myogenic vasoconstriction

28
Q

Equation for flow across whole circulation

A

Cardiac output (flow)= blood pressure/total peripheral resistance

29
Q

How is blood pressure regulated in many tissue beds at once

A

Cardiovascular centre in medulla sends signal via sympathetic nervous system which innervates arterioles and causes them to constriction

30
Q

Why does blood flow to specific organs decrease as arterial blood pressure is regulated within the body

A

Baroreceptors detect decrease in blood pressure, decreasing flow to blood vessels as vasoconstriction occurs only in specific tissues which preserve blood pressure

31
Q

3 Hormones that control and regulate arterial blood pressure

A

Vasopressin
Angiotensin
Adrenaline
Leading to vasoconstriction

32
Q

Why is capillary density important

A

Ideally suited to enhance diffusion
Specially designed to minimise diffusion distance and maximise surface area and time for diffusion

33
Q

What is the purpose of capillary exchange

A

Delivery of metabolic substrates to the cells of the organism - ultimate function of CVS

34
Q

Capillary networks in highly metabolically active tissues

A

Denser capillary network
(e.g lung has the highest capillary network to allow most gas diffusion, followed by myocardium/brain and skeletal muscle)

35
Q

Biggest tissue in body, and it’s characteristic of blood flow

A

Skeletal muscle
Huge capacity but limited flow at rest

36
Q

Continuous capillary structure

A

Single file endothelial cells with water filled gap junctions between them
Small molecules able to pass through gaps

37
Q

Fenestrated capillary structure

A

Endothelial cells have greater gaps between them allowing larger molecules to pass through
e.g gut

38
Q

Discontinuous capillary structure

A

Larger gaps between endothelial cells
E.g bone marrow and liver

39
Q

What type of capillary is in the blood brain barrier

A

Continuous with no gap junctions

40
Q

How does blood flow into and out of capillaries

A

Blood forced into capillary at high pressure due to hydrostatic force, some fluid is forced out of gaps between capillaries

41
Q

What force pushes blood into capillaries

A

Hydrostatic pushing force

42
Q

What force returns blood to the capillary

A

Oncotic pulling force (osmotic)

43
Q

Bulk flow hypothesis

A

Volume of protein free plasma filters out of capillary, mixes with surrounding interstitial fluid (IF) and is reabsorbed

44
Q

Starlings hypothesis

A

Net fluid movement - hydrostatic pressure and oncotic pressure

45
Q

What occurs when the pressure inside the capillary is greater than in the IF

A

Ultrafiltration

46
Q

What occurs when the inward driving pressures exceed the outward pressures across the capillary

A

Reabsorption

47
Q

What is the significance of ultrafiltration being more effective than reabsorption

A

Role of lymphatic system

48
Q

Role of lympathic system

A

Venous return - in one direction
Lymphatic capillaries collect tissue fluid and return it to circulation

49
Q

Where does the lymphatic system connect to the circulation

A

Right lymphatic duct - thoracic duct
Right and left subclavian vein

50
Q

Main characteristic of lymphatic system

A

No pump to induce flow
3L of fluid returned per day

51
Q

Why do lymph nodes swell during illness

A

Bacteria and virus in tissue fluid passes through lymph nodes, immune system activated in nodes, swelling occurs and bacteria and viruses targeted

52
Q

When does oedema ensure

A

When rate of production is greater than rate of drainage

53
Q

Elephantiasis is

A

Parasitic blockage of lymph nodes

54
Q

Characteristics of lymphatic system

A

Blind - ended, single-layered and contain large permeable water filled one way channels

55
Q

What is capillary density proportional to

A

Metabolic activity

56
Q

Arterioles are the

A

Major resistance vessels

57
Q

Intrinsic factors affecting arterioles

A

Chemical and physical (metabolic activity and stretch) to match blood flow to needs

58
Q

Intrinsic factors affecting atterioles

A

Neural and hormonal (SNS activity and adrenaline) to regulate arterial blood pressure

59
Q

Smooth muscle tone affects

A

Radius, which affects flow

BRS 6: Cardiovascular And Respiratory Medicine (12 decks)

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