Control of Blood Vessels: Peripheral Resistance

Question 1

What does the blood vessel radius depend on

Answer 1

active tension exerted by smooth muscle (vascular smooth muscle)
passive elastic properties of wall (elastin and collagen)
blood pressure inside vessel
(tissue pressure outside vessel - veins)

Question 2

What is the law of laplace?

Answer 2

distending pressure = wall tension / radius

where pressure = intra - extravascular pressure

Question 3

What maintains vessel calibre?

Answer 3

distending pressure and Tw (wall tension)

Question 4

Rearrange equation for distending pressure to find wall tension and radius

Answer 4

Tw = P x r

r = Tw / P

Question 5

Compare wall tension between small and large vessels and why?

Answer 5

smaller in small vessels

increase in radius increases wall tension

Question 6

What may occur if distending pressure is too high?

Answer 6

vessel rupture

>1000mmHg

Question 7

How do blood vessels resist increasing pressure?

Answer 7

elastic tissue develops tension passively in response to a rise in pressure to confer stability
adish

Question 8

What can smooth muscle develop?

Answer 8

active tension, which is independent of distending pressure

Question 9

What does active control of vessel calibre allow?

Answer 9

redistribution of blood flow
control of pre/post capillary sphincters
regulation of vascular tone and control of blood pressure

Question 10

What is vascular tone?

Answer 10

degree of constriction/dilatation

Question 11

In vasoconstriction what tension is acting?

Answer 11

increased active tension

decreased passive tension

Question 12

In vasodilatation, what tension is acting?

Answer 12

decreased active tension

increased passive tension

Question 13

Which vessels does vasomotor tone describe?

Answer 13

arterioles and arteries

Question 14

Which vessels does venomotor tone describe?

Answer 14

venules and vein

Question 15

What factors affect vascular smooth muscle contraction?

Answer 15

nerves
hormones
endothelium-derived vasorelaxants
endothelium-derived vasoconstrictors
metabolites
myogenic mechanisms

Question 16

What other NTs may cause vasocontriction?

Answer 16

ATP and NPY

tend to work with NA

Question 17

How do nerves affect vascular smooth muscle?

Answer 17

noradrenaline released from sympathetic nerve varicosity
binds to α2 and α1 on SM - vasoconstriction
binds to β2 - vasodilation
primarily activates α1 adrenoceptors in most vascular beds

Question 18

How do hormones affect vascular smooth muscle?

Answer 18

Catecholamines -
eg. noradrenaline, adrenaline (constrict/dilate)

Peptides - eg. vasopressin, angiotensin (constrict)
bradykinin (dilate)

Question 19

Which endothelium-derived vasorelaxants affect vascular smooth muscle?

Answer 19

PGI2 - prostacyclin
NO - nitric oxide
EDHF - endothelium-derived hyperpolarising factor

Question 20

Which endothelium-derived vasoconstrictants affect vascular smooth muscle?

Answer 20

endothelin

Question 21

How do metabolites affect vascular smooth muscle?

Answer 21

increase lactate, increase H+, released K+, generation of adenosine from breakdown of ATP - vasodilatation

systemic circulation - high O2, low CO2 - localised constriction
pulmonary vasculature - high O2, low CO2 - dilatation

VICE VERSA

Question 22

Where is myogenic mechanisms important?

Answer 22

important in cerebral vasculature

and kidney

Question 23

Why are myogenic mechanisms important?

Answer 23

important contributer to autoregulation of blood flow

Question 24

How do myogenic mechanisms affect vascular smooth muscle? (autoregulation of blood flow)

Answer 24

increased pressure is sensed, arteries stretch causing vasoconstriction
offsets increased flow (due to increased pressure) by increasing resistance

Question 25

What are extrinsic control mechanisms primarily concerned with?

Answer 25

regulation of arterial BP

Question 26

How does this autoregulatory range help predict pathologies?

Answer 26

if increase in pressure exceeds certain value, vessels cannot contract enough - risk of stroke
pressure decreases too much, too much dilatation - risk of unconsciousness and ischaemic damage

Question 27

What differs between different vascular beds?

Answer 27

function differs
can behave differentially depending on the situation