VPT 311: General and Systemic Veterinary Pharmacology (2+1)

FLUID MOSAIC MODEL

• Biological membranes may be viewed as mosaics of functional units composed of lipoprotein complex.
• Most membranes are composed of a fundamental structure called the unit membrane or plasma membrane, that is 80 to 100 A^ο thick, surrounds single cells and nuclei. 
• Complex barriers such as the intestinal epithelia and the skin are composed of multiples of this functional structure.
• The plasma membrane consists of a bilayer of thic lipids with their hydrocarbon chains oriented within to form a continuous hydrophobic phase and their hydrophilic heads oriented outward.
• Individual lipid molecules in the bilayer can move laterally, making the membrane fluid, flexibile, electrically resistant and relatively impermeabe to highly polar molecules. 
• This view of membrane structure is known as the fluid mosaic model.  
  • Membrane proteins embedded in the bilayer serves as receptors to elicit electrical or chemical signaling pathways and provide selective targets for drug action.
  • The proteins are able to freely float through the membrane and some of the intrinsic ones, which extend through the full thickness of the membrane, surround fine aqueous pores. Paracellular spaces or channels also exist between certain epithelial or endothelial cells and other proteins have enzymatic or carrier properties.
  • Biological membranes behave as if they were lipoids punctured by aqueous pores and allow drugs and physiological materials cross by passive or carrier mediated process. Which mechanism operates is determined by the physicochemical properties of drugs and the options available in the membrane.