Cell physiology I

A cell is a functioning entity if it can control its internal chemical and physical environment. Specialization of function is facilitated by subcellular division into compartments (organelles) and crucial to this compartmentalization are membranes that control fluxes of water and solutes.This contribution is largely concerned with the plasma membrane, which separates the extracellular space from the cytoplasmic compartment. The chemical constituents of the plasma membrane and their general roles are described. The role of the plasma membrane in regulating the ionic composition of the intracellular space (in particular how K+, Na+, Cl−, Ca2+ and pH concentration differences are maintained) are discussed. How flux of other solutes (e.g. glucose) is controlled is mentioned. The division of ion channels into voltage-gated, ligand-gated and mechanically-activated channels and their common features is considered. The cellular biology of exocytosis, what functions it underlies, and the steps that characterize the phenomenon are also discussed.