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NSG 785 - Clinical Reasoning in Pharmacotherapeutics > Pharmacodynamics 2 - Mechanisms of Drug Action - ANS as a model > Flashcards

Pharmacodynamics 2 - Mechanisms of Drug Action - ANS as a model Flashcards

1
Q

What is the ANS

A

Autonomic Nervous System

- INVOLUNTARY

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2
Q

What is the main function of the ANS?

A
  • maintaining homeostatic function
  • regulates internal environment
    e. g. heart, gut, lungs etc.
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3
Q

Outline the x2 branches of the ANS

- states key roles (individual & combined)

A

x2 branches with different function & structure:

  1. Sympathetic (fight/flight/fright)
    > prepares body for action
    > speeds up HR
  2. Parasympathetic (rest/digest)
    > slows HR

the influence of these systems produces the homeostatic balance

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4
Q

Basic ANATOMY of the ANS

A
  • sympathetic & parasympathetic branches arise from the Spinal cord
  • both have ganglia
    > break in the nerve coming out of the spinal cord
    > synaptic gap
    > post-ganglionic nerves that go to various parts of the body
  • neuroeffector junction
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5
Q

What part of the spinal cord does the sympathetic system arise from?

Describe the response

A
  • from the thoracic & lumbar sections (middle) of the spinal cord
  • paravertebral sympathetic chain
  • activation is an all or nothing response
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6
Q

What part of the spinal cord does the parasympathetic system arise from?

A
  • from the medullary & sacral regions of the spinal cord
  • goes to discrete organs, single nerve tracts to…
    e. g. eye, lacrimal & salivary glands
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7
Q

State the main x2 SYMPATHETIC NEUROTRANSMITTERS

A

NORADRENALINE (norepinephrine)

ADRENALINE (epinephrine)

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8
Q

State the main x2 SYMPATHETIC RECEPTORS on SMOOTH MUSCLE

A 
ADRENERGIC RECEPTORS  (ADRENOCEPTORS)
> divided in alpha- & beta-receptors with subtypes
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9
Q

Identify the key PARASYMPATHETIC NEUROTRANSMITTER

A

ACETYLCHOLINE

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10
Q

Identify the key PARASYMPATHETIC RECEPTORS on smooth muscle

A

CHOLINOCEPTORS

> muscarinic receptors on smooth muscle

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11
Q

Upon activation of the sympathetic nervous system:

- what neurotransmitters are released & from where?

A

1) noradrenaline released at the sympathetic nerve endings onto the smooth muscle (neuroeffector junctions)
> e.g. myocardium, bronchi

It’s effects are SUPPLEMENTED by the action of ADRENALINE (which enhances the ‘all or nothing’ response

2) noradrenaline + adrenaline released into the bloodstream from the ADRENAL MEDULLA
- acts on smooth muscle via a variety of ADRENOCEPTORS

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12
Q

Outline the FOUR MAJOR SUB-TYPES of ADRENOCEPTORS

A
  • α1 and α2

- β1 and β2

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13
Q

Specify the distribution of adrenoceptor sub-type:
α1 in various tissues & organs (2)
> effect of stimulation

A
  1. SMALL SURFACE blood vessel in the surface of skin & gut are predominantly α1
    > vasoconstriction
  2. LIVER
    > glycogenolysis
    (process by which glycogen, the primary carbohydrate stored in the liver and muscle cells, is broken down into glucose to provide immediate energy and to maintain blood glucose levels during fasting)
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14
Q

Specify the distribution of adrenoceptor sub-type:
α2 in various tissues & organs (1)
> effect of stimulation

A

SYMPATHETIC NERVE ENDINGS

> inhibition of noradrenaline release

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15
Q

Specify the distribution of adrenoceptor sub-type:
β2 in various tissues & organs (6)
> effect of stimulation

  • specify receptor target & action
A
  1. LARGE DEEP blood vessels (muscles)
    > vasodilation
  2. BRONCHIAL TREE
    > bronchodilation
    * β2 agonists
  3. UTERUS
    > relaxation
    * β2 agonist can be used to delay premature labour
  4. SKELETAL MUSCLE
    > muscle tremor
    * high doses of β2 agonist can cause this (e.g. salbutamol)
  5. CILIARY MUSCLE (EYE)
    > relaxation
    * β2 blockers used to treat glaucoma by increasing aqueous humor
  6. LIVER
    > glycogenolysis
    (process by which glycogen, the primary carbohydrate stored in the liver and muscle cells, is broken down into glucose to provide immediate energy and to maintain blood glucose levels during fasting)
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16
Q

Explain the physiological benefits of stimulating adrenoceptor subtypes in the blood vessels by the sympathetic nervous system?

A

In situations where one needs to be ‘primed for action’ this causes:

  • stimulation of α1 adrenoceptors in the small surface blood vessels in the surface of the skin & intestine causing VASOCONSTRICTION
  • stimulation of β2 adrenoceptors in the large deep vessels of the muscles causing VASODILATION

This diverts (causes a big shift in) blood to where it is needed in the muscles, away from the skin & intestine

17
Q

Distribution in various tissues & organs of adrenoceptor sub-type: β1
> effect of stimulation

  • specify receptor target & action
A 
1. HEART
> increased HR
> Increased contractility
> decreased arrhythmia threshold
* β1 antagonist (blocker) will reduce the above
  1. JUXTAGLOMERULAR CELLS
    > increased renin release causing higher levels of angiotensin II –> vasoconstrictor
    * β blockers (β1 antagonist) used in treatment of hypertension, antagonise the release of renin
18
Q

State the 3 main physiological changes that occur upon sympathetic system activation & why…
- specify the receptors & neurotransmitters involved

A

Due to the COMBINED actions of NORADRENALINE & ADRENALINE at α- and β-adrenoceptors the following effects occur:

  • increased heart rate
  • shift of blood to larger blood vessels
  • bronchodilation
19
Q

Outline the amount of activity at receptors by noradrenaline & adrenaline.

A

NORADRENALINE has greater activity at α-adrenoceptors then at β-adrenoceptors.

ADRENALINE has equal activity at α- and β-adrenoceptors.

20
Q

SYMPATHOMIMETICS

A

Drugs that

  • act as AGONISTS at adrenoceptors
  • MIMIC STIMULATION of the SNS
21
Q

SYMPATHOLYTICS

A

Drugs that

  • acts as ANTAGONISTS at adrenoceptors
  • MIMIC ‘DAMPENING’ of the SNS, may be thought of as allowing the parasympathetic NS to dominate
22
Q

Outline the effects of NORADRENALINE AS DRUGS

> main effects & therefore e.g. of uses

A

NORADRENALINE (mainly α-stimulation)

> vasoconstriction (α1-) - used to raise BP (after shock) or to reduce local blood flow (in surgery)

23
Q

Outline the effects of ADRENALINE AS DRUGS

> main effects & therefore e.g. of uses

A 
ADRENALINE (both α- and β-stimulation)
> vasoconstriction (α1-), uses as for noradrenaline, also to increase duration of local anaesthetics by constricting surface blood vessels 
e.g. lignocaine with adrenaline
> increased heart rate (β1-)
> bronchodilation (β2-)
24
Q

What is an important consideration related to usage of Noradrenaline & Adrenaline as drugs

A

VERY SHORT PLASMA HALF-LIFE

- have to be administered parenterally which limits versatility as drugs

25
Q

Four main groups of drugs affecting the SNS

A
  1. Alpha-agonists
  2. Beta-agonists
  3. Alpha-antagonists (alpha-blockers)
  4. Beta-antagonists (beta blockers)
26
Q

CARDIOPROTECTION

A

Reducing sympathetic NS effects

- Stopping the action of noradrenaline & adrenaline

27
Q

Neuroeffector junction

- state the neurotransmitters involved

A
  • adrenaline & noradrenaline is released from here to have action on the muscle
  • innervates the smooth muscle of the body & certain glands (sweat, adrenal)
28
Q

What is the MAIN therapeutic effect of:

Alpha-agonists

A

VASOCONSTRICTION

29
Q

What is the MAIN therapeutic effect of:

Beta-agonists

A

BRONCHODILATION

30
Q

What is the MAIN therapeutic effect of:

Alpha-antagonists

A

VASODILATION

alpha-blockers

31
Q

What is the MAIN therapeutic effect of:

Beta-antagonists

A

CARDIOPROTECTION

(beta blockers)

NSG 785 - Clinical Reasoning in Pharmacotherapeutics (4 decks)

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