Module 4d: vasoactive drugs Flashcards
What are the divisions of peripheral nervous system?
somatic: motor and sensory
Autonomic: sympathetic + parasympathetic
What is the autonomic ns responsible for?
involuntary control of automatic body functions
Describe the sympathetic division of ANS
Thoracolumbar outflow
Postganglionic postganglionic neurotransmitter is noradrenaline
Alpha + beta receptors
Describe the parasympathetic division of ANS?
Craniosacral outflow
postganglionic neurotransmitter= Ach
Nicotinic and muscarinic receptors
What is the first stage in the stress response?
Humoral activatiion with release of hormones:
- Defence of blood volume
- Increase aldosterone and ADH
- Mobilisation of glucose stores
- inhibits insulin
What is the second stage of stress response?
Neural activation: haemodynamics:
- increased sympathetic outflow
- Blood flow increased to heart, lungs, brain and muscle
- Blood flow decreased to GIT, kidney, liver and skin
What is the last response in stress response?
series of neurohumoral responses
Which organs are supplied by ANS
Eye
Glands: Sweat &
Salivary
Heart
Lung
Stomach & GIT
Liver & Gallbladder
Bladder
Uterus
External genitalia
What is the adrenal medulla made of?
specialised sympathetic ganglion with NO post ganglionic fibres
Post ganglionic fibres are secretory cells
Medulla secretes:
- noradrenaline(70%)
- adrenaline
- dopamine ( small amounts)
What are the 2 neurotransmitters in ANS?
Ach- parasympathetic division
Noradrenaline- sympathetic division
What are the 2 types of receptors in ANS?
Cholinergic- binds Ach
Noradrenergic: binds noradrenaline
What is the distribution of cholinergic receptors in body?
all autonomic ganglia including adrenal medulla
all parasympathetic postganglionic nerve terminals
Sympathetic postganglionic nerve terminals in SWEAT GLANDS ONLY
Somatic NS- NMJ
What cholinergic receptor subtypes do you get?
Nicotinic:
- skeletal NMJ + all autonomic ganglia
- Stimulated by nicotine and Ach
- Inhibited by neuromuscular blocking agents
Muscarinic:
- at parasympathetic postganglionic fibres
- stimulated by muscarine and Ach
- Inhibited by atropine and glycopyrrolate
What are the signs of parasympathetic excess?
Blindness (ptosis)
Bronchial secretions
Bronchospasm
Bradycardias
“B”eristalsis (peristalsis) → diarrhoea, vomiting
Bile secretion
Bladder contraction
What are the distribution and subtypes of adrenergic receptors?
Distribution: only found on sympathetic postganglionic nerve terminals
Subtypes:
Alpha:
- a1: post-synaptic: smooth muscle vasoconstriction
- a2: pre-synaptic: inhibits further NA release
Beta:
- B1: increased contractility, HR, AV node conduction
- B2: Increased skeletal muscle dilatation, bronchial relaxation, uterine relaxation
How does neostigmine works
It stimulates the PNS by blocking AchE. Increases Ach and will displace neuromuscular blocking agents= facilitating reversal of drugs.
How does neostigmine cause side effects?
Build up of Ach (parasympathetic stimulator) leads to parasympathetic effects
How does muscarinic blockade of PNS work?
postganglionic PNS receptors are muscarinic and blocked-> blocks muscarinic effects (e.g. atropine, glycopyrrolate)
What are B1 agonists named and what do they do?
They are called inotropes and increases force of contraction
What are a1 agonists named and what do they do?
They are called vasopressers and raises BP
Which 2 neurotransmitters are inotropes and vasopressors?
Adrenaline(all a +b) and NA(a1,a2,B1)
What neurotransmitter is a vasopressor but not an inotrope?
phenylephrine (a1 only)
What other neurotransmitter is also an inotrope
dobutamine
Which neurotransmitter releases NA from the sympathetic terminals as well as directing a +B effects
Ephedrine
What will be given to get a1 agonist only?
Phenylephrine
What will be given to get only a2 agonist?
Clonidine
Dexmedetomidine
What will be given for both B1+ B2 effects
Isoprenaline
What will be given for B2 effects?
Salbutamol
What are alpha receptor antagonists/blockers do and give 3 examples?
antihypertensives
Examples:
- Phentolamine-a1 + a2
- Phenoxybenzamine- a1 non-competitive
- Prazosin + doxazosin-a1
What does all B-blockers do?
competetive with varying B1 + B2 effects
Bradycardia, antiarrythmics, sedative, lower BP
Decrease cardiac mortality
Bronchospasm in asthmatics
Inhibit gluconeogenesis in liver and lipolysis
What is an example of alpha + beta blocker?
Labetalol-predominantly B blocker
What are the vasopressors used and when do you use them?
- Ephedrine: management of hypotension, raises BP + gives tachycardia(Beta effects dominate)
- Phenylephrine: vasopressor in obstetric spinal anaesthesia. Extremely potent a1 agonist. MUST BE DILUTED
When are inotropes used?
critically ill patients who need inotropic support(sepsis/ccf)
Given via central line
