Peripheral Resistance Flashcards

1
Q

Most important factor in determining resistance

A

Arteriolar diameter

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2
Q

Factors affecting blood vessel radius

A

Active tension exerted by smooth muscle
Passive elastic properties of wall (elastin & collagen)
BP Inside vessel

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3
Q

Formula for Distending Pressure

A

Wall tension/Radius

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4
Q

Formula for wall tension

A

Pressure x Radius

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5
Q

Compare wall tension of capillaries and aorta and why

A

Tw is much higher in aorta than capillaries to avoid wall damage

As result of smaller radius (Tw= P x r)

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6
Q

What does an increase in vessel radius cause in terms of tension

A

An increase in wall tension (e.g. aneurysm)

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7
Q

What part of vessels controls radius

A

Smooth muscle is responsible for developing tension

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8
Q

Importance of active control of vessel calibre

A

This allows:
Redistribution of blood flow
Control of pre/post capillary sphincters
Regulation of vascular tone and control of blood pressure

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9
Q

What happens to active tension and passive tension during vasoconstriction

A

Increased active tension

Decreased passive tension

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10
Q

What happens to active tension and passive tension during vasodilatation

A

Decreased active tension

Increased passive tension

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11
Q

What does vasoconstriction do to blood vessels

A

SM contracts and lumen is smaller

Greater resistance

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12
Q

Effect of Sympathetic nervous system on blood vessel dilation

A

Neurotransmitters released via vesicles (mainly NA)

Alpha1 adrenoceptor activation by NA causes vasoconstriction (most important)

Same with a2

Beta2 on SM stimulation causes vasodilatation

KEY TAKEAWAY - GENERALISED INCREASE IN SYMPATHETIC ACTIVITY, THERE IS VASOCONSTRICTION (a1) IN MOST NERVES; INCREASE IN RESISTANCE AND BP

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13
Q

Hormones affecting vascular smooth muscle contraction

A

Catecholamines
- Noradrenaline
- Adrenaline
(constrict/dilate)

Peptides

  • Vasopressin, Angiotensin (constrict)
  • Bradykinin
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14
Q

Intrinsic Mechanisms causing vasorelaxation/vasodilation

A

PGI2 - Prostacyclin
NO - Nitric Oxide
EDHF - Endothelium-derived hyperpolarising factor (mostly pathological i think)

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15
Q

What changes in CO2 and O2 cause vasodilation and vasoconstriction in systemic vasculature

A

Low O2 and high CO2 as result of high metabolic activity

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16
Q

What changes in CO2 and O2 cause vasodilation and vasoconstriction in pulmonary vasculature

A
17
Q

Effect of lactate, H+, K+ and adenosine changes on blood vessel calibre

A
18
Q

Response of blood vessels to stretch as result of increased BP - Autoregulation of blood flow

A

Body compensates with vasoconstriction to increase resistance to compensate increased driving force so that flow remains constant

19
Q

What happens to autoregulation if BP gets too high/low

A

If BP leaves the autoregulatory range, the blood loses the ability to effectively autoregulate and flow increases/decreases unnecessarily

20
Q

Extrinsic control mechanisms involved with regulation of arterial BP

A

Nerves, hormones