Medical Physiology - Transport of Substances Across Cell Membranes

Medical Physiology - Transport of Substances Across Cell Membranes
The disparities in the composition of internal and extracellular fluids result from the transport processes of cell membranes. The distinctions encompass the subsequent: Extracellular fluid has elevated sodium and chloride concentrations, and a reduced potassium content. Conversely, intracellular fluid exhibits higher quantities of phosphates and proteins compared to extracellular fluid. The cell membrane comprises a lipid bilayer with embedded protein molecules. The lipid bilayer serves as a barrier to the passage of most water-soluble substances. Nonetheless, the majority of lipid-soluble compounds can traverse the lipid bilayer directly. Protein molecules within the lipid bilayer form an alternative transport mechanism. Channel proteins facilitate a hydrous passage for molecules to traverse the membrane. Carrier proteins associate with certain molecules and then undergo conformational alterations that facilitate the translocation of molecules across the membrane. Transport across the cell membrane occurs by diffusion or active transport. Diffusion refers to the random movement of molecules either via the intermolecular gaps of the cell membrane or in conjunction with a carrier protein. The energy responsible for diffusion is derived from the inherent kinetic motion of matter. Active transport refers to the translocation of molecules across the membrane facilitated by a carrier protein, occurring against an electrochemical gradient. This process necessitates an energy source in addition to kinetic energy.