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Blood Pressure 2 Flashcards

1
Q

What are Arterioles?

A

Part of microcirculation (connects arteries to capillaries)
Major resistance vessels
Greatest resistance to blood flow
Contribute 60% TPR
Largest pressure drop in vasculature (90mmHg to 40mmHg)

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2
Q

What are the features of Arterioles?

A

Thinner walls

Lack tunica externa

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3
Q

Large Arterioles

A

Extensive tunica media

Thin layers of smooth muscle

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4
Q

Smaller Arterioles

A

Tunica media: single layer of smooth muscle arranged spirally around endothelium

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5
Q

What are the properties of Arterioles?

A

Rich supply of sympathetic nerve fibres

Large amount of smooth muscle

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6
Q

What does radius of Arterioles depend on?

A

contraction state of the smooth muscle

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7
Q

What is the regulation of Arterioles?

A

Regulation of radius
Regulation of resistance
Regulation of BF

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8
Q

What is the function of Arterioles?

A

Control blood flow to capillary beds

Regulation of MAP

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9
Q

What is the basal vascular tone?

A

Some degree of smooth muscle contraction

Gives indication of vasodilatory capacity

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10
Q

High vascular tone

A

Large vasodilatory capacity

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11
Q

Low vascular tone

A

Low vasodilatory capacity

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12
Q

Vasodilatory

A

Dilation of blood vessels

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13
Q

What does radius (R) of a vessel strongly influence?

A

Resistance

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14
Q

What is the equation of control of radius?

A

R = 1/r^4

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15
Q

Vasoconstriction

A

Increase contraction

Decrease radius

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16
Q

Vasodilation

A

Decrease contraction

Increase radius

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17
Q

What are the 3 primary factors that determine the resistance to BF within a single vessel?

A
  1. Vessel diameter
  2. Vessel length
  3. Viscosity of blood
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18
Q

Why does the vessel diameter change?

A

Contraction and relaxation of vascular smooth muscle in wall of blood vessel

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19
Q

What controls the radius of Arterioles?

A

Intrinsic and extrinsic factors

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20
Q

What is intrinsic factors?

A

Local BF regulation

Related to metabolic needs of organ

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21
Q

What is extrinsic factors?

A

Systemic control of TPR

Closely related to MAP

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22
Q

Intrinsic factors

A

Regulating radius of Arterioles at local level

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23
Q

What are the properties of intrinsic factors?

A

Primarily chemical influences
Locally secreted chemicals
Myogenic property
Temperature

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24
Q

Primarily chemical influences

A

Metabolite changes
Match BF momentary metabolic needs
Increase BF in response to increase in metabolic activity

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25
What are the components of active Hyperaemia?
``` Increase carbon dioxide Increase lactic acid Increase H+ Increase K+ Leads to vasodilation ```
26
What do active cells use?
More oxygen and fuel (glucose/fatty acid) | Need more nutrients
27
What does metabolising tissue produce?
Carbon dioxide
28
What does increase in carbon dioxide cause?
Smooth muscle in vessel to dilate Blood vessels dilate Increase BF to metabolising tissue
29
What acts on arteriolar smooth muscle?
Decrease in oxygen | Increase in carbon dioxide
30
What is the effect of vasodilation?
Increase blood flow
31
Locally secreted chemicals (vasoactive substances)
Do not act directly on smooth muscle Endothelial cells release chemical mediators Regulate radius of Arterioles
32
What are examples of vasodilator substances?
Nitric oxide = NO = EDRF Histamine (inflammation on allergic reaction) Not derived from endothelial cells Stimulate NO release
33
What are examples of vasoconstrictor?
Endothelin | Act on endothelial cells
34
What is myogenic property?
Increase blood flow and increase blood pressure in Arterioles Increase in perfusion pressure Increase stretch of arteriolar wall
35
What does contraction of smooth muscle cause?
Vasoconstriction
36
Vasoconstriction
Decrease radius Increase resistance Decrease blood flow
37
What is the purpose of myogenic property?
Keep blood flow constant
38
Temperature
Heat , increase blood flow Useful therapeutic agent Cold, decrease blood flow Useful therapeutic agent (reduce swelling) Counteracts histamine induced vasodilation
39
extrinsic factors
Regulating radius of Arteriole at systemic level Acts to control TPR Control the systemic vascular resistance > control MAP
40
What is MAP directly proportional to
TPR
41
What is TPR altered by?
Neural and hormonal mechanism
42
What is neural ?
Sympathetic control Sympathetic innervation smooth muscle of Arterioles Increase sympathetic activity
43
Noradrenaline
Released from sympathetic nerve endings | Binds to adrenergic receptors
44
Noradrenaline
Alpha 1 receptors | Adrenal medulla20% of adrenomedullary output
45
Adrenaline
Alpha1 and beta2 receptors Adrenal medulla 80% of adrenomedullary output
46
Vasopressin
Posterior pituitary gland
47
Angiotensin II
Renin-Angiotensin-aldosterone system (RAAS)
48
Vasopressin/ADH
Increase water reabsorption by kidneys | Causes vasoconstriction > Increase TPR
49
Angiotensin II
Hormonal pathway - RAAS Release of aldosterone (Na+ reabsorption) Causes vasoconstriction Increases TPR
50
Properties of veins
Large diameter Small amount of smooth muscle Thin walls (high compliance) - less resistance to blood flow Blood reservoir - 64% of TBV in systemic vein at rest
51
Valves
Peripheral veins have valves Many lie between skeletal muscles Large veins - valves about 2-4cm apart
52
Unidirectional blood flow
Blood only flows towards heart
53
What is the function of valves?
Counteract gravitional effect Minimise backflow of blood Temporarily support columns of blood
54
Venous return
Flow of blood back to the heart
55
What factors influence venous return?
Blood volume (increase blood volume increase venous return) Venomotor tone (increase venomotor tone, vasoconstriction of veins, increase venous return) Skeletal muscle pump Respiratory pump Cardiac suction
56
Arterial
High pressure High flow velocity Pulsatile
57
Veins
Low pressure Low flow velocity Non pulsatile
58
Arterioles
Largest drop in MAP | Site of highest vascular resistance
59
Capillaries
Lowest velocity
60
Skeletal muscle pump
One way valve that direct blood away from limb and towards the heart Veins located within large muscle groups
61
Skeletal muscle pump
Skeletal muscle contracts: Veins compressed Decreases venous capacity Increases venous pressure Exercise: Increase muscle activity Increase blood out of veins Increase blood to the heart
62
Cardiac suction
During ventricular systole, the tendinous cord pull AV valves cusps downwards, slightly expanding the atrial space and creating a slight suction that draws blood from venae cavae and pulmonary veins

Physiology II (16 decks)

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