Pharmacology (Dan) Flashcards
What are the 2 major divisions in the peripheral nervous system?
- Efferent neurons
- Afferent neurons
> seonsory neurons that carry info to CNS from sensory receptors
What are the 2 types of efferent neuron and what does each do?
1) Somatic motor neurons: project to skeletal muscle and control posture and movement (voluntary)
2) Autonomic neurons: efferent neurons that innervate smooth and cardiac muscle (involuntary)
Describe the anatomy of the somatic motor pathway
- Cell bodies of somatic neuron in ventral horn of spinal cord
- myelinated axon runs to skeletal muscle
- May branch and innvervate more than 1 muscle cell (motor units)
- Neurotransmitter = ACH
- Acts on ACH receptors
Describe the anatomy of the sympathetic pathway
- Neurons originate in the thoracic and lumbar regions of spinal cord
- Consists of 2 efferent neurons:
> Preganglionic: from CNS to autonomic ganglion (short)
Uses ACH and nicotinic ACH receptor
> Postganglionic: from ganglion to target organ (long)
Uses noradrenaline and adrenergic receptor
Describe the anatomy of the parasympathetic pathway
- Neurons originate in brain stem or sacral regions of spinal cord Consists of 2 efferent neurons: > Preganglionic (long) Uses ACH and nicotinic ACH receptor > Postganglionic (short) Uses ACH and muscarinic ACH receptor
Describe the transmission of a signal at the neuromuscular junction
- choline acetyltransferase transfers acetyl group form acetyl-CoA to choline to make ACH
- Packaged into vesicles
- Action potential arrives - depolarises nerve terminal
- Causes voltage gated Ca2+ channels - calcium influx
- Ca2+ causes vesicles containing ACH to fuse with the presynaptic nerve terminal membrane
- ACH released into synaptic cleft (regulated exocytosis)
- ACH binds to alpha subunit of ACH receptors
- Triggers the opening of ion channels in post synaptic membrane
- Na+ influx causes depolarisation (end plate potential (EPP))
- If large enough, will cause action potential
- ACH hydrolysed by acetylcholinesterase into choline and acetic acid
- Reuptake of choline by membrane choline carrier into nerve terminal to make more ACH
What is vesamicol and how does it work?
- Cholinergic antagonist
- Causes a reversible, non competitive block to vesicular acetylcholine transporter (VAChT)
- VAChT responsible for transporting newly sysntesised ACH to vesicles for packaging
What is Botulinum toxin and how does it work?
- A drug that inhibits acetylcholine release
- Prevents acetylcholine release by enzymatically cleaving the proteins (e.g synaptobrevin) required for docking of vesicles to the presynaptic membrane
How is botulinum toxin type A administered and what is it used to treat?
Used to treat certain dystonias (abnormalities of muscle tone resulting in spasm) such as blepharospasm (spasmodic eye closure)
- Injected into muscle to cause paralysis for ~12 weeks
- Can also be used as a treatment for incontinence
How do competitive neurotransmitter blocking drugs work, why are they used clinically and what are the 5 main drugs?
- Bind to nicotinic ACH receptors and block the entry binding of ACH
- Used as anesthetic as they cause paralysis
5 main: - Pancuronium
- Vecuronium
- Atracurium
- Cisatracurium
- Rocuronium
What are the common side effects of competitive neurotransmitter blocking drugs?
- Histamine release
- Vagal blockage (vagal nerve blokade - vagal nerve assists in loweing heart rate)
- ganglion blockade
- sympathomimetic actions
What is the duration and side effects of Pancuronium?
- Relatively long duration
- Does not block ganglion
- Does not cause histamine release
- Can cause tachycardia (abnormally high heart rate)
What is the duration and side effects of Vecuronium?
- Commonly used
- Recovery after 20-30 minutes - attractive for short procedures
- No cardiovascular effects
What is the duration and side effects of Atracurium?
- Duration of action of 15-30 minutes
- Only stable at low pH and kept cold
- In body pH and temp, decomposes in plasma so does not depend on renal or hepatic excretion
- Therefore used in renal and hepatic disease
- Can cause histamine release
What is the duration and side effects of Cisatracurium?
- Isomer of atracurium
- does not cause histamine release
What is Suxamethonium and how does it work?
- Depolarizing neuromuscular blocking drug
- Works in 2 phases:
1) Depolarising phase Suxamethonium binds to nicotinic ACH receptors and causes them to open - end plate depolarisation - Last longer than ACH
- Usually rapidly degraded by plasma pseudocholinesterase, but in some people (1 in 3000) they inherit atypical form of enzyme so block may last hours
- Prolonged receptor activation - continuous action potentials - muscle twitches
2) Desensitizing phase - Inactivation of voltage gated Na+ channels in surrounding mucle fibre membranes - no action potentials
- Transformation of activated receptors to desensitized state
What type of disease is Myasthenia Gravis (MG), what causes it and how is it treated?
- Autoimmune disease
- Circulating heterogeneous IgG antibodies cause loss of nicotinic acetylcholine receptor function
- Choice of drugs are acetylcholinesterase inhibitors:
> Neostigmine or Physostigmine - Less ACH degradation, higher chance it will stimulate receptor
Also, immunological treatments:
> Azathioprine - interferes with IgG antibody production
What are the differences between the autonomic and somatic nervous systems?
A controls involuntary actions
S controls voluntary actions
A - primary transmitters - ACH and NA
S - Primary transmitters ACH
A interacts with nicotinic and muscarinic receptors
S interacts with nicotinic only
A innervates tissue via 2 neurons connected by ganglion
S innervates skeletal muscle via single motor neuron
What are the different types of adrenoreceptors and are they pharmacologically distinct?
Alpha 1, Beta 1, Alpha 2 and Beta 2 adrenoreceptors Pharmacologically distinct (targets for different drugs)
What are the different types of muscirinic ACH receptors and are they pharmacologically distinct?
- G protein coupled receptors, subtypes M1 - M3
- M1 in brain, M2 in heart and M3 in smooth muscle and glands
- Pharmacologically indistinct
What are the main drug types used to treat autonomic diseases?
- Muscarinic agonists and antagonists
- a1, B1, a2 and B2 agonists and antagonists
- Nicotinic agonists (ganglionic stimulants) and blockers
What is the main muscarinic agonist and what is it used to treat?
Pilocarpine (choline ester)
- Used to treat glucoma; reduces intraocular pressure by contraction of ciliary muscles, increasing aqueous outflow
What is the main muscarinic antagonist and what is it used to treat?
Atropine
Used in anaesthetic; prevents slowing of heart and bronchial secretion/reflex contraction
- Another mACH antagonist is hyoscine (causes more drowsiness and amnesia than atropine)
What other drug type might be used in the parasympathetic nervous system?
Acetylcholinesterases
- common is Physostigmine
What is released in a sympathetic nervous response?
Noradrenaline from sympathetic nerve terminal
- in some forms of stress, adrenaline also released from adrenal medulla
What is a sympathomimetic drug?
A drug that partially or completely mimics the actions of normal sympathetic agonists (nor and adrenaline)
What is phenylephrine and what does it cause?
alpha 1 agonist
- used in decongestant prep - reduction if bronchial secretions, also in eye drops to dilate pupils
What is clonidine and what does it do?
alpha 2 agonist
- centrally acting hypotensive drugs (lowers blood pressure)
What is Prazosin and what does it cause?
alpha 1 antagonist
- used to treat benign prostatic hyperplasia (BPH) in men and high blood pressure
also called alpha blockers
What are beta blockers and what are they used to treat? Give an example drug
Beta 1 antagonists
- used to treat blood pressure and angina; decreased cardiac output
most common is Atenolol
What is salbutamol and what is it used to treat?
Beta 2 agonist
- Treatment of acute asthma, causes bronchial dilation
What are the main pathologies affecting the cardiovascular system?
- Hypertension
- Hypotension
- Angina pectoralis
- Heart failure
- Cardiac arrythmia
- Atherosclerosis
What is hypertention and what is it measured in?
Hypertension is high blood pressure
- Measured in mmHg at systolic and diastolic
- Hypertension indicated at pressure reading og 160mmHg/100mmHg
What are the risk factors of hypertension?
Smoking Obesity Dietary influence Diabetes - Lifestyle changes should be considered before therapeutic intervention
What 3 drug types can be used to treat hypertension?
- Thiazide diuretics
- Beta blockers (beta 1 adrenoreceptor antagonists)
- Angiotensin converting enzyme (ACE) inhibitors
Where do thiazide diuretics act and what do they cause?
- Site of action is the distal region of the kidney
- Act upon specific transporter proteins that allow reabsorption of salts from the tubule to the blood
- Transport process is electrically neutral
- Regulation of salt excretion also regulates water excretion by osmosis
What is the thiazide diuretic mechanism of action?
- Bind to the chloride-binding site of the sodium chloride co-transport system, located on luminal side of tubule
- Co- transport of sodium and chloride ions inhibited so prevents salt re absorption into the blood
- Retention of osmotic balance keeps water in distal tubule
- Water excreted in urine
- Reduction in blood volume
What region of the thiazide diuretic interacts with the binding site on the co-transport protein?
The thiazide region
What are the side effects of thiazide drugs?
- Increased frequency of urination
- Erectile dysfunction
- Increased LDL in blood
- Gout