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Pharmacology Year 2 > SNS agonists > Flashcards

SNS agonists Flashcards

1
Q

Most sympathetic post-ganglionic neurones release noradrenaline. State two exceptions.

A

Adrenal medulla – adrenaline (80%) and noradrenaline (20%)

Sweat glands – acetylcholine

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2
Q

State the difference between directly and indirectly acting SNS agonists

A

DIRECT = binds to the adrenoceptor and mimic the action of adrenaline and noradrenaline

INDIRECT = inhibits the uptake and breakdown systems leading to the accumulation of neurotransmitter in the synaptic cleft

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3
Q

Describe the mechanism of action of the four different types of adrenoceptor.

A 
ALL adrenoceptors are G-protein coupled 
𝛼1 = via PLC, IP3, DAG
𝛼2 = decreases cAMP (inhibitory)
β1 = increases cAMP
β2 = increases cAMP
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4
Q

State the main effector functions mediated by β1 receptors

A

HEART – increase heart rate + increase contractility

KIDNEYS – increase renin release => increase blood pressure

Lipolysis

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5
Q

State the main effector functions mediated by β2 receptors

A

LUNGS - Bronchodilation

LIVER - Hepatic glucose output (glycogenolysis + gluconeogenesis)

BLOOD VESSELS - Vasodilation of vessels supplying skeletal muscle

URETERS and BLADDER - relaxes detrusor

UTERUS - relaxation of uterine smooth muscle

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6
Q

State some effector functions that are mediated by both 𝛼 and β receptors

A

SALIVARY GLANDS - thick viscous secretion

GASTROINTESTINAL - decreased motility and tone, sphincter contraction

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7
Q

What receptors are responsible for the increased and decreased production of aqueous humour by the ciliary body?

A

β receptors - control the enzyme that makes the aqueous humour

𝛼1 receptors are involved in vasoconstriction of the vessels in the ciliary body = reduced blood flow within the ciliary body

𝛼2 receptors also decrease humour production

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8
Q

State the main effector functions mediated by 𝛼1 receptors

A

EYE - pupil dilation/mydriasis (contraction of radial muscles of the iris)

URETERS and BLADDER - constriction of trigone and sphincter

SKIN - piloerection

BLOOD VESSELS - vasoconstriction of vessels supplying skin, mucous membranes and splanchnic area

Glycogenolysis, gluconeogenesis and lipolysis

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9
Q

Describe the action of pre-synaptic alpha-2 receptors

A

Have a negative influence on noradrenaline synthesis and release

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10
Q

Describe the relative receptor selectivity of adrenaline and noradrenaline.

A

Noradrenaline is more selective for ALPHA-receptors

Adrenaline is more selective for BETA-receptors

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11
Q

Summarise the biosynthesis pathway of noradrenaline

A

Tyrosine => DOPA; catalysed by tyrosine hydroxylase

DOPA => Dopamine; catalysed by DOPA decarboxylase

Uptake of Dopamine into vesicle

Dopamine => Noradrenaline; catalysed by dopamine β-hydroxylase

Vesicle exocytosis and noradrenaline release.

Uptake 1 (neuronal re-uptake): converted to metabolites by Monoamine oxidase A (MAO-A)
in mitochondria

Uptake 2 (extra neuronal uptake): degradation by COMT

𝛼2 receptors are located at the nerve terminal and inhibit vesicle exocytosis (when bound to noradrenaline)

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12
Q

List five directly acting SNS agonists

A 
Phenylephrine (a1>a2)
Clonidine (a2>a1)
Dobutamine (b1>b2) 
Salbutamol (b2>b1)
 Isoprenaline (b1=b2)
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13
Q

What are the symptoms of anaphylaxis, and why is adrenaline used in the treatment?

A

In anaphylaxis:

  • IgE-coated mast cell degranulation and systemic release of inflammatory mediators
  • Increase in capillary permeability => increased movement of fluid into the tissues => depleted circulating fluid volume => drop in blood pressure
  • Contraction of bronchial smooth muscle and constriction of muscles around the throat => respiratory distress
  • Constriction of GI smooth muscle => vomiting and diarrhoea

Adrenaline causes β2 mediated bronchodilation, β1 mediated tachycardia and 𝛼1 mediated vasoconstriction

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14
Q

What are some other clinical uses of adrenaline?

A
  • In asthma emergencies (i.m., s.c.)
  • Acute bronchospasm associated with chronic bronchitis
    or emphysema
  • Cardiogenic shock (sudden inability of heart to pump sufficient oxygen-rich blood)
  • Used in spinal anaesthesia to maintain BP (peripheral vasculature relaxed due to sympathetic block of anaesthetic)
  • Used in local anaesthesia to cause vasoconstriction prolonging action (prevent clearance)
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15
Q

List and categorise the unwanted effects of adrenaline

A

Secretions are reduced and thick

CVS:

  • tachycardia, palpitations, arrhythmias, cold extremities, hypertension
  • Overdose of adrenaline => cerebral haemorrhage, pulmonary embolism

CNS: minimal

GIT: minimal

Skeletal muscle: tremor

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16
Q

How does phenylephrine differ from adrenaline chemically?

A

Selectivity: a1»a2»>b1/b2

Chemically related to adrenaline but more resistant to COMT (not MAO)

17
Q

List the clinical uses of phenylephrine

A
  • Vasoconstriction
  • Mydriasis
  • Nasal decongestant
18
Q

Describe the selectivity of clonidine

A

Selectivity: a2»a1»>b1/2

19
Q

List and explain the clinical uses of clonidine

A

Treatment of hypertension and migraine

  • It reduces sympathetic tone by 𝛼2 adrenoceptor mediated
    presynaptic inhibition of NA release
  • It has a central action in brainstem within
    baroreceptor pathway to reduce
    sympathetic outflow
20
Q

How does isoprenaline differ from adrenaline chemically?

A

Selectivity: ß1=ß2»»α1/𝛼2

Chemically related to adrenaline but more resistant to MAO and uptake 1

21
Q

List the clinical uses of isoprenaline

A
  • Cardiogenic shock
  • Acute heart failure
  • Myocardial infarction
22
Q

State the caution related to β2 stimulation by isoprenaline

A

β2-stimulation in vascular smooth muscle supplying skeletal muscle => fall in venous blood pressure which triggers a reflex tachycardia via the stimulation of baroreceptors.

23
Q

State the selectivity of dobutamine and its clinical use? Why might it be better than isoprenaline?

A

Selectivity: β1»β2»>α1/α2

Clinical use = Cardiogenic shock

  • Lacks isoprenaline’s reflex tachycardia
  • Plasma half life 2 minutes (rapidly metabolised by COMT)
24
Q

State the selectivity of salbutamol (Ventolin). What is it resistant to?

A

Selectivity: b2»b1»>a1/2

It is a synthetic catecholamine derivative with relative resistance to MAO and COMT

25
Q

Explain the clinical uses of salbutamol

A

Treatment of Asthma:

  • β2 mediated relaxation of bronchial smooth muscle
  • Inhibition of release of bronchoconstrictor substances from mast cells

Treatment of threatened premature labour:
- β2 mediated relaxation of uterine smooth muscle

26
Q

What are the side effects associated with salbutamol?

A

Reflex tachycardia
Tremor
Blood sugar dysregulation

27
Q

Which adrenoceptor mediates the enhancement of lipolysis in adipose tissue?

A

β3 adrenoreceptor

Pharmacology Year 2 (32 decks)

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