NEET MDS Lessons
Pharmacology
CHOLINERGIC DRUGS
Produce actions similar to Acetylcholine (Ach)
Cholinergic Agonists
1 Acetylcholine 2 Methacholine 3. Carbachol 4 Bethnechol
Alkaloids
1.Muscarine 2 Pilocarpine 3. Arecoline
MECHANISM OF ACTION
I Heart- hyperpolarizes the SA node and decreases the rate of diastolic depolarisation. thus the frequcncy of impulse generation is decreased. bradycardia.
2 Blood vessels- vasodilatation
3. Smooth muscles - increased contraction. increased tone. increased peristalsis.
4. Glands- increased sweating. increased lacrimation.
5 Eye- contraction of the circular muscle of iris (miosis).
Nicotinic action
Autonomic ganglia - stimu1ation of sympathetic and parasympathetic system.
Skeletalmuscles - contraction of fibres.
CNS..No effect as it does not penetrate the blood-brain barrier.
Toxic effects
Flushing. sweating.salivation. cramps. belching. involuntary mictuirition. defaccation.
Contraindication
1.. Anginapectoris- decreases the coronary flow.
2 Pepticulcer - increases the gastric secretion
3 Asthma- bronchoconstriction
4 Hyperthyroidisim
Cholinomimetic Alkaloids
Pilocarpine
Prominent muscarinic actions. causes marked sweating. salivation. Increase of secretions. small doses cause fall in BP but higher doses increase in BP. Applied to the eye cause miosis. fall in intraocular tension
Uses
I. .Open angle glaucoma
2. To counteract mydriasis
Anticholinesterase
They inhibit the enzyme cholinestrase and prolong the action of Ach
Reversible
Physostigamine, Ncostigamine, Pyridostigamine, Ambenonium, Edrophonium, Demecarium
Irreverible
Dyflos. Echothiphate.
Pharmacological Actions
I Ganglia - persistent depolarisation of ganglionic nicotinic receptors.
2 CVS - unprcdictable as Muscarinic-I receptor causes bradycardia but ganglionic stimulation
tachycardia.
3. Skeletal muscles - as Ach is not destroyed and rebinds to the same receptor or it diffuses on to the neighbouring receptors to cause repetitive firing. twitching and fasciculations.
Uses
I As miotic
a) Glaucoma : Acute congestive (narrow angle) glaucoma, Chronic simple (wide angle) glaucoma
b) Counter act atropine mydriasis.
2) Post operative paralytic ileus
3) Myasthenia gravis
4) Postoperativedecurarization
5) Cobra bite
6) Belladona poisoning
7) Other drug overdoses
Calcium Channel Blocking Agents
• Act on contractile and conductive tissues of the heart and on vascular smooth muscles
• Prevent movement of extracellular calcium into the cell
– Coronary and peripheral arteries dilate
– Myocardial contractility decreases
– Depress conduction system
Therapeutic Actions
• Inhibit movement of calcium ions across the membranes of myocardial and arterial muscle cells. Altering the action potential and blocking muscle cell contraction
• Depress myocardial contractility
• Slow cardiac impulse formation in the conductive tissues
• Cause a fall in BP
Carbonic anhydrase inhibitors
Acetazolamide, Dichlorphenamide, Methazolamide, Ethoxzolamide
Mechanism of Action
1. Carbonic anhydrase (CA) facilitates excretion of H+ and recovery of bicarbonate by the proximal renal tubule and ciliary epithelium of the eye. Sodium is recovered in exchange for H+.
2. Inhibitors block CA block sodium recovery. A very mild diuresis is produced (this is really a side effect of their use in glaucoma) because relatively unimportant mechanism for Na recovery and because proximal tubule site means that other sodium recovery mechansims continue to process their normal fraction of the sodium load.
Methods of general anesthesia
CIRCLE SYSTEM
*HIGH-FLOW
FRESH GAS FLOW > 3 l/min.
*LOW-FLOW
FGF ok. 1l/min.
*MINIMAL-FLOW
FGF ok. 0,5 l/min.
Types of Neurons (Function)
•There are 3 general types of neurons (nerve cells):
1-Sensory (Afferent ) neuron:A neuron that detects changes in the external or internal environment and sends information about these changes to the CNS. (e.g: rods and cones, touch receptors). They usually have long dendrites and relatively short axons.
2-Motor (Efferent) neuron:A neuron located within the CNS that controls the contraction of a muscle or the secretion of a gland. They usually have short dendrites and long axons.
2-Interneuron or association neurons: A neuron located entirely within the CNS in which they form the connecting link between the afferent and efferent neurons. They have short dendrites and may have either a short or long axon.
Balanced Anesthesia
A barbiturate, narcotic analgesic agent, neuromuscular blocking agent, nitrous oxide and one of the more potent inhalation anesthetic.
Treatment modifications to consider if there are concerns regarding vasoconstrictors
- Monitor blood pressure and heart rate preoperatively
- Minimize administration of epinephrine or levonordefrin
- Monitor blood pressure and heart rate 5 min after injection
- May re-administer epinephrine or levonordefrin if blood pressure and heart rate are stable
- Continue to monitor as required
- Consider limiting epinephrine to 0.04 mg, levonordefrin to 0.2 mg
- Avoid epinephrine 1:50,000
- Never use epinephrine-impregnated retraction cord