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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
Where does neural regulation of arterial blood pressure originate from?
Regulated by the cardiovascular control centre in the medulla
26
What receptors facilitate constriction and dilation?
Adrenoreceptors: a = constriction b = dilation
27
Which hormones can mimic the sympathetic nervous system to control the heart?
Adrenaline and noraderenaline
28
Which hormones can control blood pressure by action on arterioles?
Vasopressin and Angiotensin II
29
How can resistance in vessels be adjusted?
Intrinsically and extrinsically
30
Define capillary exchange
Delivery of metabolic substrates to the cells of the organism
31
How narrow are the walls of a capillary?
1 micrometre thick
32
How are the capillaries branched?
Extensive branching - no capillary is more than a few micrometers away from tissue cell
33
The more metabolically demanding the tissue, the greater the...
Capillary density
34
What parts of the body have high capillary density?
Skeletal muscle, myocardium/brain and lungs
35
Why does the myocardium and brain need a high capillary density?
They are vulnerable to hypoxia
36
What tissue is poorly perfused?
adipose tissue
37
What shuts of arterioles/capillaries?
precapillary sphincter
38
What are the 3 main types of capillary?
Continuous Fenestrated Discontinuous
39
What are the features of continuous structured capillaries?
They contain water filled gap junctions that allow the passage of electrolytes and other small molecules
40
What are the features of fenestrated capillaries?
Leakier capillaries. | Fenestrae - slightly bigger holes called which allow larger substances to pass through
41
What are the features of discontinous capillaries
Large holes in the capillary
42
What is the importance of discontinuous capillaries?
Important in bone marrow where white cells have to get into the blood
43
What is the commonest type of capillary?
Continuous
44
What does the blood brain barrier consist of?
Tight gap junctions which ensures that substances which want to get into the brain has to diffuse across the endothelial cells
45
Define bulk flow
A volume of protein-free plasma filters out of the capillary, mixes with the surround IF and is reabsorbed
46
What are the starling forces?
Hydrostatic pressure and Oncotic pressure. These two pressures affect the movement of fluid in and out of the capillary
47
Describe the pressure differences in the arteriolar end of a capillary
Hydrostatic pressure > Oncotic pressure = Fluid leaves the capillary
48
Describe the pressure differences in the venular end of a capillary
Oncotic pressure > hydrostatic pressure = Fluid enters the capillary
49
Are there changes in oncotic pressure along a capillary?
No, oncotic pressure is the same the whole way
50
What are the function of valves in the lymphatic vessels?
Prevents the back flow of lymph
51
What is the movement of fluid in the lymph driven by?
Lymphatic pressure
52
Does the lymphatic system form a closed loop?
No, they are blind ended
53
Where does the lymph drain into?
Thoracic Duct Right Lymphatic Duct Right Subclavian Vein Left Subclavian Vein
54
How many litres of fluid is returned to the circulatory system by the lymphatic system per day?
3L
55
Describe the principle of oedema
Rate of production of fluid > Rate of removal of fluid
56
What circulatory system can be affected causing oedema?
Lymph nodes - parasitic blockage
57
What is elephantiasis caused by?
filaria - parasitic blockage of lymph nodes

Year 1: Cardiovascular System (21 decks)

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