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Renin Angiotensin Mechanism.

Principles of Pharmacodynamics.


Pharmacodynamics:

  • The branch of pharmacy that deals with the study of pharmacological actions of a drug on the body is called as pharmacodynamics.

What is "Pharmacological Action"?

  • The interaction between the drug and living components of the body resulting in modification of the body functions is called as the pharmacological action of the drug.
  • e.g. Aspirin on administration reversibly blocks enzyme prostaglandin synthetase and relieves mild to moderate pains, inflammation, and lowers elevated body temperature.

Basic types of pharmacological actions:

  • Any drug produces its pharmacological action from one of the following types.

1) Physical Action:

  • Some drugs produce their pharmacological actions in a mechanical way,
  • e.g. Osmotic diuretics, Adsorbents like kaolin in diarrhoea.

2) Chemical Reaction:

  • Some drugs interact chemically with each other to produce the effect.
  • e.g. Antacids like aluminium hydroxide gel are chemically weak alkaline drugs which interact with gastric acid and neutralise it.
3) Action through receptors:
  • Receptors are protein molecules present on the cell membrane or nucleus of the cell.
  • When receptors bind to the biological ligands like neurotransmitters, hormones, autocoids, steroids etc. the formed complex initiate chemical changes inside the cell and alters the functions.
4) Action through enzyme inhibition:
  • Enzymes are the biological catalyst which catalyses all biological reactions.
  • Some drugs cause inhibition of such enzymes, altering the outcome of the reactions.
e.g. 

5) Action by blocking ion channels:
  • Ion channels present on the cell are of different types, they regulate entry and exit of the ions.
  • The entry and exit of ions produce various effects on the cell.
  • Certain drugs modify entry and exit of such ions and affect cellular functions.
e.g.

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