NEET MDS Lessons
Pharmacology
Antiemetics
Antiemetic drugs are generally more effective in prophylaxis than treatment. Most antiemetic agents relieve nausea and vomiting by acting on the vomiting centre, dopamine receptors, chemoreceptors trigger zone (CTZ), cerebral cortex, vestibular apparatus, or a combination of these.
Drugs used in the treatment of nausea and vomiting belong to several different groups. These include:
1. Phenothiazines, such as chlorpromazine, act on CTZ and vomiting centre, block dopamine receptors, are effective in preventing or treating nausea and vomiting induced by drugs, radiation therapy, surgery and most other stimuli (e.g. pregnancy).
They are generally ineffective in motion sickness.
Droperidol had been used most often for sedation in endoscopy and surgery, usually in combination with opioids or benzodiazepines
2. Antihistamines such as promethazine and Dimenhyrinate are especially effective in prevention and treatment of motion.
3. Metoclopramide has both central and peripheral antiemetic effects. Centrally, it antagonizes the action of dopamine. Peripherally metoclopramide stimulates the release of acetylcholine, which in turn, increases the rate of gastric. It has similar indications to those of chlorpromazine.
4. Scopolamine, an anticholinergic drug, is very effective in reliving nausea & vomiting associated with motion sickness.
5. Ondansetron, a serotonin antagonist, is effective in controlling chemical-induced vomiting and nausea such those induced by anticancer drugs.
6. Benzodiazepines: The antiemetic potency of lorazepam and alprazolam is low. Their beneficial effects may be due to their sedative, anxiolytic, and amnesic properties
Methicillin
Methicillin is an antibiotic related to penicillin and other beta-lactam containing antibiotics. It is often used to treat infections caused by bacteria carrying an antibiotic resistance, e.g., staphylococci. As methicillin is deactivated by gastric acid, it has to be administered by injection.
Uses Methicillin serves a purpose in the laboratory to determine antibiotic sensitivity in microbiological culture.
Cells of the Nervous System
1-Neurons (Nerve Cells):function units of the nervous system by conducting nerve impulses, highly specialized and amitotic. Each has a cell body (soma), one or more dendrites, and a single axon.
• Cell Body: it has a nucleus with at least one nucleolus and many of the typical cytoplasmic organelles, but lacks centriolesfor cell division.
• Dendrites:Dendrites and axons are cytoplasmic extensions (or processes), that project from the cell body. They are sometimes referred to as fibers. Dendrites (afferent processes) increase their surface area to receive signals from other neurons, and transmit impulses to the neuron cell body.
• Axon: There is only one axon (efferent process) that projects from each cell body.
It carries impulses away from the cell body.
2-Glial cells: do not conduct nerve impulses, but support, nourish, and protect the neurons. They are mitotic, and far more numerous than neurons.
Astrocyte: A glialcell that provides support for neurons of the CNS, provides nutrients regulates the chemical composition of the extracellularfluid.
• Oligodendrocyte: A type of glialcell in the CNS that forms myelin sheaths.
• Microglia:The smallest glialcells; act as phagocytes (cleaning up debris) and protect the brain from invading microorganisms.
• Schwann cell:A cell in the PNS that is wrapped around a myelinatedaxon, providing one segment of its myelin sheath.
Kinins
Peptide that are mediated in the inflammation.
Action of kinin:
On CVS: vasodilatation in the kidneys, heart, intestine, skin, and liver. It is 10 times active than histamine as vasodilator.
On exocrine and endocrine glands: kinin modulate the tone of pancreas and salivery glands and help regulate GIT motility, also affect the transport of water and electrolytes, glucose and amino acids through epithelial cell transport.
Buspirone
1. Short half-life (2–4 hours).
2. Relieves anxiety.
3. Does not act as an anticonvulsant.
4. Is not a good muscle relaxant.
5. Minimum abuse potential.
Operator position
For the right-handed operator, the 8 and 10 o’clock position and for left-handed operators, the corresponding 2 and 4 o’clock position almost always allows for optimal visualization of the injection field.
Histamine:
Involved in inflammatory and anaphylactic reactions
Local application causes swelling redness, and edema, mimicking a mild inflammatory reaction.
Large systemic doses leads to profound vascular changes similar to those seen after shock or anaphylactic origin.
Storage: widely distributed; in tissues, primarily in mast cells; in blood- in basophils, platelets; non-mast cell sites (epidermis, CNS, regenerating cells)
Histamine Stored in complex with:
Heparin
Chondroitin Sulfate
Eosinophilic Chemotactic Factor
Neutrophilic Chemotactic Factor
Proteases
Release: during type I (IgE-mediated) immediate hypersensitivity rxns, tissue injury, in response to some drugs
a. Process: Fcε receptor on mast cell or basophil binds IgE, when Ag binds → ↑ PLC activity → histamine
Symptoms: bronchoconstriction, ↓ Pa, ↑ capillary permeability, edema
Action
H1 receptors are located mainly on smooth muscle cells in blood vessels and the respiratory and GI tracts. When histamine binds with these receptors producing the following effects.
-Contraction of smooth muscle in the bronchi and bronchioles producing bronchoconstraction.
-stimulation of vagus nerve endings to produce reflex bronchoconstraction and cough.
-Increased permeability of veins and capillaries, which allows fluid to flow into subcutaneous tissues and form edema (little lower blood pressure).
-Increased secretion of mucous glands. Mucosal edema and increased nasal mucus produce the nasal congestion characteristic of allergic rhinitis and the common cold.
-Stimulation of sensory peripheral nerve endings to cause pain and pruritus.
Histamine promotes vasodilation by causing vascular endothelium to release nitric oxide. This chemical signal diffuses to the vascular smooth muscle, where it stimulates cyclic guanosine monophosphate production, causing vasodilation.
H2-receptors present mostly in gastric glands and smooth muscle of some blood vessels. When receptors are stimulated, the main effects are increased secretion of gastric acid and pepsin, increased rate and force of myocardial contraction.
The H3-receptor functions as a negative-feedback mechanism to inhibit histamine synthesis and release in many body tissues. Stimulation of H3 receptors opposes the effects produced by stimulation of H1 receptors.
The H4- receptor is expressed in only a few cell types, and their role in drug action is unclear.
Drugs cause release of histamine:
Many drugs can cause release of histamine in the body.
-Intracutaneouse morphine injection in humans produced localized redness, localized edema and a diffuse redness. This is due to release of histamine.
-I.V. inj of curare may cause bronchial constriction due to release of histamine.
-codeine , papaverine, meperidine (pethedine), atropine, hydralizine and sympathomimetic amines, histamine releases by these drugs may not be significant unless they are administered I.V in large doses
Pharmacological effects
- If injected I.V. (0.1 mg of histamine) causes a sharp decline in the blood pressure, flushing of the face and headache.
- There is also stimulation of gastric acid secretion.
- If this injection is given to an asthmatic individual, there will be a marked decrease in vital capacity and a sever attack of asthma.
Circulatory effects of histamine:
The two factors involved in the circulatory action of histamine are:
Arteriolar dilatation and
Capillary permeability
So it leads to loss of plasma from circulation
Effect on gastric secretion:
Histamine is a potent stimulant of gastric Hcl secretion.