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Year 1: Cardiovascular System > 5. The Microcirculation > Flashcards

5. The Microcirculation Flashcards

1
Q

Describe the arrangement of the microcirculation

A

1st order arterioles, Terminal arterioles, capillary, pericytic (post-capillary venule), Venule

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2
Q

Define blood flow rate

A

Volume of blood passing through a vessel per unit time

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3
Q

What is the equation for blood flow rate?

A

F = delta P/R

F = Blood flow rate
delta P = Pressure gradient
R = Vascular resistance

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4
Q

Define resistance

A

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

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5
Q

What are the factors that affect resistance?

A

Blood viscosity
Vessel radius
Vessel length

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6
Q

Which is the main factor affecting resistance?

A

Vessel radius. Vessel length and blood viscosity is fairly constant

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7
Q

Resistance is directly proportional to…

A

1/r^4

r = radius

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8
Q

What happens when the BP increases?

A

The difference in pressure increases and the blood flow rate increases

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9
Q

What happens when arteriolar vasoconstriction occurs?

A

The resistance increases but the blood flow rate decreases

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10
Q

What is the mean arterial pressure/normal blood pressure in any artery?

A

93mmHg

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11
Q

Where does blood pressure changes occur?

A

Across the arterioles

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12
Q

Why does the system lower blood pressure as blood cross the arterioles?

A

This is so that blood passes relatively slowly through the capillary bed to allow the exchange of nutrients

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13
Q

What is blood pressure at the end of the capillaries?

A

Venous blood so 0mmHg

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14
Q

How can the blood flow rate equation be written as in terms of an organ?

A

F Organ = delta P (=MAP)/R Organ

Because the pressure going out pretty much 0, the delta P is just going to be around MAP

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15
Q

What is the major determinant of the blood flow in the body?

A

Resistance to the arterioles in the organ

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16
Q

Describe vascular tone

A

Arteriolar smooth muscle usually displays a state of partial constriction

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17
Q

What are the functions of the radii of arterioles being able to be adjusted independently?

A
  1. Match blood flow to the metabolic needs of specific tissues - this is regulated by local intrinsic control
  2. Help regulate arterial blood pressure - regulated by extrinsic controls
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18
Q

Define active Hyperemia

A

An increase in organ blood flow that is associated with increased metabolic activity of an organ or tissue

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19
Q

What change is detected in the tissues resulting in the arterioles vasodilating?

A

Metabolism increases and oxygen consumption increases

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20
Q

What two environments do arterioles respond to?

A

Physical and chemical environment

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21
Q

What happens when blood temperature decreases?

A

The microcirculation will detect this change and make the arteriolar smooth muscle contract so that less blood reaches the surface and so less heat is radiated away

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22
Q

What is the equation for cardiac output?

A

CO = MAP/TPR

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23
Q

What is total peripheral resistance?

A

The sum of the resistance of all arterioles in the body

24
Q

What pathways change the radii of the arterioles?

A

Neural or hormonal pathways

25
Q

Where does neural regulation of arterial blood pressure originate from?

A

Regulated by the cardiovascular control centre in the medulla

26
Q

What receptors facilitate constriction and dilation?

A

Adrenoreceptors:
a = constriction
b = dilation

27
Q

Which hormones can mimic the sympathetic nervous system to control the heart?

A

Adrenaline and noraderenaline

28
Q

Which hormones can control blood pressure by action on arterioles?

A

Vasopressin and Angiotensin II

29
Q

How can resistance in vessels be adjusted?

A

Intrinsically and extrinsically

30
Q

Define capillary exchange

A

Delivery of metabolic substrates to the cells of the organism

31
Q

How narrow are the walls of a capillary?

A

1 micrometre thick

32
Q

How are the capillaries branched?

A

Extensive branching - no capillary is more than a few micrometers away from tissue cell

33
Q

The more metabolically demanding the tissue, the greater the…

A

Capillary density

34
Q

What parts of the body have high capillary density?

A

Skeletal muscle, myocardium/brain and lungs

35
Q

Why does the myocardium and brain need a high capillary density?

A

They are vulnerable to hypoxia

36
Q

What tissue is poorly perfused?

A

adipose tissue

37
Q

What shuts of arterioles/capillaries?

A

precapillary sphincter

38
Q

What are the 3 main types of capillary?

A

Continuous
Fenestrated
Discontinuous

39
Q

What are the features of continuous structured capillaries?

A

They contain water filled gap junctions that allow the passage of electrolytes and other small molecules

40
Q

What are the features of fenestrated capillaries?

A

Leakier capillaries.

Fenestrae - slightly bigger holes called which allow larger substances to pass through

41
Q

What are the features of discontinous capillaries

A

Large holes in the capillary

42
Q

What is the importance of discontinuous capillaries?

A

Important in bone marrow where white cells have to get into the blood

43
Q

What is the commonest type of capillary?

A

Continuous

44
Q

What does the blood brain barrier consist of?

A

Tight gap junctions which ensures that substances which want to get into the brain has to diffuse across the endothelial cells

45
Q

Define bulk flow

A

A volume of protein-free plasma filters out of the capillary, mixes with the surround IF and is reabsorbed

46
Q

What are the starling forces?

A

Hydrostatic pressure and Oncotic pressure. These two pressures affect the movement of fluid in and out of the capillary

47
Q

Describe the pressure differences in the arteriolar end of a capillary

A

Hydrostatic pressure > Oncotic pressure = Fluid leaves the capillary

48
Q

Describe the pressure differences in the venular end of a capillary

A

Oncotic pressure > hydrostatic pressure = Fluid enters the capillary

49
Q

Are there changes in oncotic pressure along a capillary?

A

No, oncotic pressure is the same the whole way

50
Q

What are the function of valves in the lymphatic vessels?

A

Prevents the back flow of lymph

51
Q

What is the movement of fluid in the lymph driven by?

A

Lymphatic pressure

52
Q

Does the lymphatic system form a closed loop?

A

No, they are blind ended

53
Q

Where does the lymph drain into?

A

Thoracic Duct
Right Lymphatic Duct
Right Subclavian Vein
Left Subclavian Vein

54
Q

How many litres of fluid is returned to the circulatory system by the lymphatic system per day?

A

3L

55
Q

Describe the principle of oedema

A

Rate of production of fluid > Rate of removal of fluid

56
Q

What circulatory system can be affected causing oedema?

A

Lymph nodes - parasitic blockage

57
Q

What is elephantiasis caused by?

A

filaria - parasitic blockage of lymph nodes

Year 1: Cardiovascular System (21 decks)

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