The selectively permeable
cell membrane is surrounded on both sides by a
solution containing
water as a solvent and many dissolved
solutes. It is composed of a
phospholipid bilayer with many embedded
molecules such as
glycolipids, cholesterol and
proteins of various types. The bilayer and its embedded
molecules maintain a delicate balance between the
extracellular and
intracellular fluids.
To maintain
homeostasis in the
cell, the levels of
solutes in the ICF and ECF must remain relatively constant. The
permeability of the
plasma membrane is regulated to maintain this balance of
solutes. Changes in the permeability alter the
transport of substances across the
plasma membrane.
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1 - Anatomy and Physiology Basics