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Life support > CVS Vascular Tone and Vascular Smooth Muscle > Flashcards

CVS Vascular Tone and Vascular Smooth Muscle Flashcards

1
Q

What is vascular tone?

A

Degree of constriction of a blood vessel relative to maximum dilation

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2
Q

What is vascular tone controlled by?

A

Controlled by contractile state of vascular smooth muscle

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3
Q

What is vascular tone present in?

A

Vascular tone present in arteries, arterioles, veins

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4
Q

What type of vessels do not have vascular tone and why?

A

Capillaries do not contain vascular smooth muscle so not have vascular tone

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5
Q

What is vascular tone important in?

A

Vascular tone in arterioles is important in controlling total peripheral resistance and therefore blood flow to end organs
(blood flow is proportional to r^4)

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6
Q

What are the general features of constrictor responses that regulate vascular tone?

A

Act directly at VSMCs

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7
Q

What are the general features of dilator responses that regulate vascular tone?

A

Indirectly via endothelium

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8
Q

Why do we need intrinsic or local control of vascular tone?

A

Regulate local blood flow to organs/tissues

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9
Q

What do we need extrinsic control of vascular tone?

A

Regulate TPR to control blood pressure
Blood pressure is the drive for blood flow

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10
Q

What are the nerve releasing extrinsic/external controls of vascular tone?

A

Nerves releasing
-Vasoconstrictors - e.g., noradrenaline
-Vasodilators - e.g., Ach, nitric oxide

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11
Q

What are the hormone releasing extrinsic/external controls of vascular tone?

A

Vasoconstrictors – e.g., adrenaline, angiotensin II, vasopressin
Vasodilators – e.g., ANP

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12
Q

What are the steps involved in the sympathetic vasoconstrictor system?

A

The rostral ventral lateral medulla(RVLM) receives info from other brain areas like the hypothalamus
-This sends a main excitatory drive to the thoracic spinal cord intermediolateral(IML)
-The sympathetic preganglionic fibre stimulates sympathetic ganglia and this will result in sympathetic postganglionic fibres to stimulate beta 1 receptors in heart, and alpha 1 and beta 2 receptors on blood vessels via noradrenaline
-The sympathetic preganglionic fibre also stimulates the adrenal medulla which releases adrenaline that acts on alpha 1 and beta 2 receptors on vessels.

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13
Q

What do alpha 1 receptors on postsynaptic membrane do?

A

Contraction of blood vessels

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14
Q

What do alpha 2 receptors do on postsynaptic membrane?

A

Contraction of blood vessels

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15
Q

What do beta 2 receptors do on postsynaptic membrane?

A

Relaxation of blood vessels

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16
Q

What does AT1 receptor do on presynaptic membranes?

A

Increase release of NA(hence increasing RAAS and increasing sympathetic activity)

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17
Q

What does alpha 2 receptors on the presynaptic membrane do?

A

Reduce release of NA hence vasodilation

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18
Q

What does local K+/adenosine levels do on presynaptic membrane

A

Reduce release of NA hence vasodilation

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19
Q

What are sympathetic vasoconstrictor nerves controlled by?

A

Controlled by brainstem

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20
Q

What receptor does noradrenaline activate and what does this cause?

A

NA activates alpha1-adrenoceptors on vascular smooth muscle cells
alpha1-adrenoceptors cause vasoconstriction

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21
Q

What is the best way to describe sympathetic nerve activity?

A

Sympathetic nerve activity is TONIC (fires about 1 action potential / s)

22
Q

What does tonic sympathetic activity set?

A

Tonic sympathetic activity sets vascular tone

23
Q

What does a fall in ongoing sympathetic activity produce?

A

This means that a FALL in ongoing sympathetic activity produces vasodilatation

24
Q

A decrease in what mechanism is an important principle in pharmacological treatment of CVD like hypertension?

A

Decrease in mechanisms coupling sympathetic activity to vascular tone is an important principle in pharmacological treatment of cardiovascular disease

25
Q

What are the roles of sympathetic vasoconstrictor nerves?

A
  1. Contract arterioles
  2. Distinct RVLM neurons sympathetic pathways innervate different tissues
  3. Produce precapillary vasoconstriction to increase interstitial fluid reabsorption
  4. Produce vasoconstriction to increase venous return
26
Q

What does contracting arterioles do and maintain and what does it allow?

A

-Produces vascular tone
-Maintains arterial blood pressure and blood flow to brain/myocardium
-Allows vasodilatation mechanisms and increased blood flow to occur

27
Q

What does producing precapillary vasoconstriction result in and what does this support?

A

-Reduce capillary pressure
-Increase reabsorption due to increase influence of oncotic pressure
-Support maintenance of blood volume

28
Q

What does producing vasoconstriction increase?

A

-Increase venous return to heart
-Increases stroke volume via Starling’s law

29
Q

What are vasoconstrictor hormones that control circulation?

A

Adrenaline, Angiotensin II (Ang II), Anti-Diuretic Hormone (ADH)

30
Q

What are vasodilator hormones that control circulation?

A

Atrial natriuretic peptide (ANP)

31
Q

What is adrenalines function with vascular tone, what is it released due to, from where and what does it act on?

A

-Released due to sympathetic nerve stimulation
-Mainly from adrenal glands
-Acts on alpha1-adenoceptors on vascular smooth muscle

32
Q

What is Ang II function, where is it formed and what does it act on?

A

-Formed from RAAS
-Very potent vasoconstrictor
-Acts on AT1 receptors on vascular smooth muscle

33
Q

What is the function of ADH or vasopressin, where is it released from and what does it act on?

A

Released from posterior pituitary gland
Acts on V1-receptors on vascular smooth muscle
-Vasoconstrictor

34
Q

What is the function of endothelin-1, where is it released from and what does it act on?

A

Released from endothelium
Acts on ETA receptors on vascular smooth muscle
-Vasocontrictor

35
Q

What is the function of thromboxane(TXA2), where is it released from and acts on what?

A

Released from aggregating platelets
Acts on TP receptors on vascular smooth muscle
-Vasoconstrictor

36
Q

What are the steps involved in homeostatic mechanism for ADH?

A
  1. Arterial baroreceptors and atrial volume receptors detect decrease in blood volume/pressure
  2. This results in a decrease in sensory nerve firing. The inhibitory pathway is switched off and excitatory pathway is switched on.
  3. Medulla(brainstem) hypothalamus
    -Osmoreceptors in hypothalamus are activated and increase osmolality as well as ADH release
    -The posterior pituitary gland secretes ADH
  4. ADH will act on blood vessels which will activate V1 receptors. This will result in vasoconstriction which increases blood pressure
  5. ADH will also act on kidney and activate V2 receptors. This results in aquaporins being inserted in collecting duct. This results in an increase in:
    -H20 reabsorption
    -Blood volume
    -Blood pressure
37
Q

What do vasoconstrictors activate to increase vascular tone?

A

Vasoconstrictors increase vascular tone
by activating same G-protein-coupled pathway
in vascular smooth muscle

38
Q

What pathway do vasoconstrictors activate and what does this cause?

A

Galphaq pathway
-Causes depolarisation resulting in activation of VGCCs resulting in Ca2+ entry
-Ca2+ alongside Ca2+ from influx cause contraction
-

39
Q

What is Atrial natriuretic peptide(ANP)?

A

Vasodilator hormone

40
Q

What is ANP secreted by?

A

Released by specialised atria myocytes
Secreted by increased filling pressures which stimulate stretch receptors

41
Q

Where does ANP act at and what does this activate?

A

Act at NP receptors on vascular smooth muscle
(Activate cGMP pathway like nitric oxide)

42
Q

What is ANP a biomarker for?

A

Biomarker for congestive heart failure

43
Q

What 3 ways does ANP reduce blood pressure by?

A
  1. Systemic vasodilation
  2. Dilation of renal afferent arteriole
  3. Decreases release actions of aldosterone, renin, ADH
44
Q

What does systemic vasodilation due to ANP do?

A

opposes action of NA, Adr, Ang II, ADH, ET-1, TXA2

45
Q

What does dilation of renal afferent arteriole do?

A

Increases glomerular filtration rate
Increases Na+ and H2O excretion by the kidney – Reduces blood volume

46
Q

What is central for controlling blood pressure and blood flow?

A

Regulation of vascular tone (controlling blood vessel radius) is
central for controlling blood pressure and blood flow

47
Q

Why do we need to increase vasoconstriction in some conditions?

A

in some conditions, we need to increase vasoconstriction
to increase TPR and raise blood pressure back to normal
to maintain correct end organ perfusion

48
Q

What receptor does NORAD have a hiigher affinity to in comparison to adrenaline?

A

Noradrenaline (NORAD) has higher affinity for α -than -adrenoceptors
Adrenaline has a higher affinity for - than -adrenoceptors

49
Q

What receptor does NORAD primarily act at and what effect does this have?

A

NORAD is given to primarily act at alpha1-adrenoceptors on VSMCs
to increase TPR and increase blood pressure

50
Q

How are NORADs cardiac protective?

A

Without having significant actions on heart (1) – cardiac protective, doesn’t
make the heart work hard to increase BP, blood flow
e.g., important in conditions such as sepsis, severe heart failure

Life support (38 decks)

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