Ever since the reactive oxygen species (ROS) were discovered in biology, the researchers have tried to understand the impact of these molecules in physiological pathways. They are known to be toxic since they are involved in plethora of diseases that include metabolic disorders, genetic diseases, neurodegenerative diseases, diabetes, cancer and premature aging. No doubt, at high concentrations, they are harmful for living organisms, but at moderate and optimum levels, ROS play an important role as regulatory and signaling molecules and regulate various biological pathways and are critical for healthy cell function. At the cellular level, ROS regulate growth, apoptosis, autophagy, memory, blood pressure, cognitive function, immune function; enable the response to growth factor stimulation and the generation of the inflammatory response. They are involved in the cross-linking of the extracellular matrix and regulate many cellular processes, including differentiation, proliferation, growth, cytoskeletal regulation, migration and contraction. They are involved in gene activation and modulation of chemical reactions in the cell. They also act as mediators in the biosynthesis of prostaglandins, act as signaling molecules within the individual cell and among cells. They also influence contractility of vascular smooth muscle cells, control vascular endothelial cell proliferation, migration and mediate platelet activation. Thus, ROS, originally envisioned as a necessary evil of oxidative metabolism & a product of an imperfect system are involved in regulation of normal physiological functions and this review tries to unlock the conception about their involvement in normal physiology.
