Regulation of Male and Female Reproductive Functions

Abstract

Reproduction is an important biological process of species evolution, it is leading to new offspring from parents. The pituitary gland (the master gland) in the endocrine system in coordination with the hypothalamus plays a vital role in the reproductive system, differentiation, and different physiological functions in the entire stages of life and its circadian rhythm in both males and females. The chapter deals with the prominent role played by the brain, endocrine system, and gonads axis through complex communicating signals. The male gonads are the location of testicles, interstitial tissue (Leydig cells), and peritubular myoid cells. Sertoli cells act as “nurse and stem” cells, spermatogenesis, spermiogenesis were explained. Gonad’s steroid hormones (Androgens) characteristics are specified in male reproductive activity, biological actions along with the regulator hormones (follicle-stimulating hormone, luteinizing hormone, and hypothalamic–pituitary–Leydig cell axis. Ovaries are female reproductive glands. The chapter describes the tissue zones of ovaries, puberty, and two main functions (exocrine and endocrine) controlled and coordinated by the hypothalamus and the pituitary. Female sex hormones in pre-puberty (Estrogen) and post-puberty (estradiol, estrone, progesterone, and inhibin), and sources (ovarian follicle and corpus luteum) were discussed in detail. Structure of steroid hormones discussed with the role of the endometrium, regulation of ovarian functions, and puberty by endocrine and immune system. The different phases of the ovarian cycle are explained to regulate gonadotropins, follicular growth, steroid synthesis, non-functional corpus albicans (infertile ovum), and regulation of the ovarian cycle (pre-ovulatory phase, ovulation phase, and post-ovulatory phase). The involvement of estradiol metabolites, enzyme aromatase, the hormone oxytocin, matrix metalloprotease, cytokines, and vasoconstriction in corpus luteum formation is related along with maintenance and regression. Synthesis of ovarian hormones (β-estradiol, estrone, and estriol) after puberty discussed with important functions of progesterone, regulatory roles of inhibin, activin, and follistatin in the physiology of testis and ovary. Dehydroepiandrosterone (DHEA) involvement was discussed for menopause in elderly women and andropause in men. The chapter declares that the classic theory of cessation of oocytes production after birth was canceled. Both human neonatal and adult ovarian germline stem-cell precursors (ovarian surface cells) have the capability for oogenic/differentiating and producing functional oocytes, so it renews the oocyte pool (neo-oogenesis) and ensures renewal during the prime reproductive period, with follicular cooperation under the regulation of the endocrine, immune systems, and cellular support. After the prime reproductive period, aging starts, and menopause occurs because of the immunoregulatory changes that cause cessation and terminate neo-oogenesis and follicular renewal in vivo despite the existence of germline stem cell precursors. The rest of the oocytes in the primordial follicles retain ovarian function but advancing age (aging oocytes) correlates positively with the occurrence of fetal chromosomal abnormality. This chapter discusses the topics related to regulation of male and female reproductive functions.