The gonads—testes in males and ovaries in females—are central to mammalian reproduction, performing the dual functions of gamete production and hormone secretion. These hormones are indispensable not only for reproductive activity but also for the development and maintenance of secondary sexual characteristics that distinguish the sexes.

Testis: The testes are paired, oval-shaped organs housed in the scrotum. Their two major functions are the production of sperm (spermatogenesis) and the secretion of male sex hormones. Internally, each testis contains numerous seminiferous tubules, the site of sperm formation. Scattered between these tubules are Leydig cells, which produce androgens, primarily testosterone.

• Spermatogenesis: Testosterone regulates the initiation and maintenance of sperm production.
   
• Secondary sexual traits: It promotes the growth of facial and body hair, deepening of the voice, increased muscle mass, and development of male genitalia during puberty.
   
• Sex drive (libido): Testosterone is essential in maintaining male sexual behavior.
   
• Bone and muscle growth: Its anabolic effects enhance bone density and muscle strength.

Ovary: The ovaries are small, almond-shaped organs located in the pelvic cavity. They are responsible for producing eggs (oogenesis) as well as female sex hormones. The outer cortex contains follicles at different stages of maturation, each surrounding an oocyte. After ovulation, the ruptured follicle develops into the corpus luteum, which secretes hormones.

• Estrogens (e.g., estradiol): Stimulate follicle maturation, promote female secondary sexual traits such as breast development, fat distribution, and widening of the hips, and induce proliferation of the uterine lining in preparation for implantation.
• Progesterone: Prepares and maintains the endometrium, prevents uterine contractions during pregnancy, and supports mammary gland development for lactation.

Both estrogen and progesterone exert negative feedback on the hypothalamus and pituitary to regulate gonadotropins (FSH, LH), maintaining reproductive balance.

Together, testes and ovaries coordinate reproduction, sexual development, and species continuity.