The viability and adequacy of regenerative capacity in male vertebrates, including humans, depends on the productivity of spermatogenesis, an intricate procedure where diploid cells (spermatogonia) separate into haploid sperm that at that point combine with a solid oocyte to yield an egg.
2.4.1 Testicular Spermatogenesis
In mammalian species, spermatogenesis happens in the testicles (Su et al., 2011), which are exceptionally specific structures made up of seminiferous tubules and interstitial compartment.
The testicles create amid early embryogenesis, following acceptance by the testis determining factors (Sex deciding Region on the Y chromosome SRY, and the SRY-related protein, SOX9) (Harley et al., 2003).
Spermatogenesis is initiated in the hypothalamous by the arrival of two pituitary hormones, viz., the luteinizing hormone (LH) and the follicle-invigorating hormone (FSH), both which experience control of gonadotropin-releasing hormone (GnRH) (Weinbauer et al., 2001). FSH applies its impacts on the Sertoli cells, though LH empowers the generation of steroid hormones (testosterone, estradiol) in Leydig cells (Weinbauer, et al., 2001; Krassas and Pontikides 2004; Su et al., 2011). Testosterone which is one of the major androgenic hormone in males, then act by means of its receptors on Sertoli cells, to stimulate/control separation of germ cells into spermatozoa. Indeed, Sertoli cells give mechanical and nourishing help to the germ cells during the spermatogenic processes, make and keep up the fitting microenvironment required through between cell inter-cells junctions (between Sertoli cell blood-testis barrier) that preclude hurtful substances from reaching developing germ cells, in this manner shielding them from cytotoxic atoms of overwhelming heavy metals. (Cheng et al., 2011; Mital et al., 2011; Papaioannou et al., 2011; Su et al., 2011).
Esfiadiol, produced from testosterone in the testis by Sertoli and Leydig cells, stimulate spermatozoa motility and is a noteworthy germ-cell survival factor (Pentikiiinen et al., 2000; Carreau and Hess 2010; Carreat et al., 2010). The testicular steroids, and different hormones created by Sertoli cells (inhibin B, follistatin, activin) and leydig cells (follistatin), direct spermatogenesis, and apply feedback/input control impact on hypothalamo-pituitary complex (Weinbauer, et a1.,2001; Akingbemi et al.,2003; de Kretser et al.,2004; Guyton and Hall 2006).
Additionally, the thyroid hormones are imperative in maintenance and upkeep of germ cells improvement/work (Krassas and Pontikides., 2004).