Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Endocrine system
Gonads

The gonads (Testis and Ovary) are the sites where Germ Cells are formed and Sex Hormones are secreted into the bloodstream. The primary biological function of these hormones is to ensure the normal execution of reproductive processes.

The testis, testis, is a paired organ of the Male Reproductive System located in the Scrotum. Within its parenchyma, alongside Spermatogenesis, the Synthesis of male sex hormones—androgens (testosterone)—takes place. These hormones are synthesized by Leydig cells located in the Mediastinum of the testis. Androgens drive The Development of the reproductive Organs and The formation of male secondary sex characteristics (such as body build, Hair growth patterns, vocal pitch, stimulation of skeletal and muscular growth, distribution of subcutaneous adipose tissue, and regulation of sperm maturation). Furthermore, androgens exhibit a pronounced anabolic effect by enhancing tissue METABOLISM.

The ovary, ovarium (Greek — oophoron), is a paired female reproductive gland situated in the pelvic cavity between the layers of the broad ligament of the Uterus. It consists of a cortical and a medullar substance. By the time of birth, the cortex contains 400,000–500,000 primary follicles. During Puberty and reproductive life (from 10–12 to 45–55 years of age), certain primary follicles begin to increase in size and produce hormones. These are referred to as secondary or maturing follicles. Over a woman's reproductive lifespan, only 400–500 follicles mature. The periodicity of follicle maturation—averaging one follicle every 28 days (ranging from 21 to 35 days)—determines the length of the Menstrual cycle. A mature follicle is known as a Graafian follicle. On the 14th day of the menstrual cycle, the Graafian follicle ruptures, a process known as ovulation, during which the mature oocyte is released into the peritoneal cavity. At the site of the ruptured follicle, a corpus luteum develops—a temporary accessory endocrine gland that produces progestogens (progesterone), the Pregnancy-maintenance hormone. It creates optimal conditions for Fertilization, implantation (nesting in the uterine wall), and the subsequent Development of the fetus. If fertilization does not occur, this corpus luteum secretes progestogens into the Blood until the onset of the next menstrual cycle and is called the menstrual corpus luteum, functioning until the next cycle begins. If fertilization takes place, a corpus luteum of pregnancy is formed, which carries out endocrine Functions throughout the entire gestational period. The Role of the corpus luteum is most critical up to 12–16 weeks of pregnancy, after which the Placenta forms and the primary role in hormone production shifts to this provisional organ. Following the cessation of its endocrine function, the corpus luteum undergoes involution, leaving behind a scar known as the corpus albicans.

Estrogens are produced by maturing follicles and, in small amounts, by the medullar substance. They regulate the development of the reproductive organs and the formation of female secondary sex characteristics.