Reactive Oxygen Species in the Reproductive System: Sources and Physiological Roles.

Reactive oxygen species (ROS) are oxygen-containing molecules which are reactive in nature and are capable of independent existence in the body. ROS comprise mostly of free radicals that contain at least one unpaired electron. Endogenous sources are the foremost birthplaces of ROS, which include mitochondrial electron transport chain, endoplasmic reticulum and peroxisome. Conversely, numerous enzymatic pathways such as xanthine oxidase and cyclooxygenase systems are among the prominent generators of cellular ROS. Major sources of ROS in the female reproductive tract include Graafian follicles, follicular fluid, fallopian tube, peritoneal cavity and endometrium. On the contrary, leukocytes, immature spermatozoa and varicocele are the key originators of ROS in the male reproductive system. For the sake of maintaining a proper oxidative balance, cells have evolved a variety of antioxidative molecules. From the physiological perspective, ROS and antioxidants are actively involved in the regulation of myriad female reproductive processes, such as cyclic luteal and endometrial changes, follicular development, ovulation, fertilization, embryonic implantation, maintenance of pregnancy and parturition. Similarly, physiological amounts of ROS are crucial in the accomplishment of various male reproductive functions as well, which include spermatozoa maturation, capacitation, hyperactivation and acrosome reaction. This chapter highlights the birthplaces of ROS in the female and male reproductive tract along with mechanisms of their production. This chapter will also put forward specific physiological roles of these reactive molecules in upholding the structural integrity and functionality of both the reproductive systems.