Biomedical of LA BDS2 Flashcards
1
Q
How does LA work?
A
- stop nerve conduction
- by blocking Na+ voltage gated channels
2
Q
Connective tissue layers
A
- epineurium
- perineurium
- endoneurium
3
Q
Susceptibility of LA block
A
- nerve axons differ in susceptibility
- Order of block: Adelta, C, AB, Aa
4
Q
Types of nerve axons
A
- anesthetise AD and C fibres for LA
5
Q
Mechanism of action
A
- LA binds to site in Na+ channel
- LA blocks channel and prevents Na+ influx
- This blocks action potential generation and propagation
- Block persists so long as sufficient number of Na+ channels are blocked
** LA can block Na+ channels in heart channels
- can cause bradycardia and hypotension
6
Q
Components of LA
A
- organic molecules: aromatic region (hydrophobic), ester/ amide bond, basic amide chain NH2 as hydrophilic
- present as hydrochloride, which renders amine base more water soluble
- partly dissociated (active in ionised form, can cross membrane only in un-ionised form)
7
Q
Why are small diameter axons more susceptible to LA block?
A
- less number of Na+ channels to block
8
Q
What about myelinated axons?
A
- Na+ channels are concentrated at nodes of Ranvier
- generate a very quick response
9
Q
Safety factor of myelinated
A
- the local currents are strong enough to flow past blocked region and to regenerate AP at the next node of Ranvier
- to block AP, LA needs to act on several nodes of Ranvier along axon
10
Q
LA constituents
A
- LA base present as HCl to increase solublity in aqueous solution
- 2-4 % solutions
- reducing agent (sodium metasulphide)
- Preservatives and fungicide
11
Q
Types of LA
A
Esters
- Cocaine
- Procaine
- Benzocaine
Amide
- Lignocaine
- Prilocaine
- Articaine
- Bupivicaine
12
Q
Disadvantages of using adrenaline?
A
- reduce blood flow
13
Q
How does vasoconstrictor works?
A
- most LA are vasodilators, hence increased blood flow will increase wash out of LA
- adrenaline and felypressin are vasoconstrictor
- hence, increase duration of action
- vasoconstrictor acts on receptors on vascular smooth muscle
14
Q
Types of Adrenoreceptors
A
- A receptors: vasocontrictor
- B2 receptor: vasodilation
- B1 receptor: reacts on cardiac muscle, increase HR (chronotropic) and force (inotropic)
15
Q
How are LA broken down?
A
- ester broken down by tissue esterases
- amide broken down by liver amidases
