Gonads

Gonads, also known as primary reproductive organs, are the organs that produce gametes and secrete sex hormones. In humans, the gonads are the ovaries in females and the testes in males. The gonads arise from the undifferentiated gonadal ridges during embryonic development and differentiate under genetic and hormonal influences. The presence of the SRY gene on the Y chromosome drives testis formation; in its absence, the gonads develop as ovaries.

Anatomy and location: ovaries are paired organs in the female pelvis; they release oocytes and produce estrogens and progesterone. Testes are paired organs located in the scrotum; they produce sperm and testosterone.

Gametogenesis: oogenesis produces ova, beginning in fetal life with meiosis I arrested until puberty and continuing with periodic meiosis II after fertilization, yielding one ovum and polar bodies. Spermatogenesis occurs continuously from puberty onward in the seminiferous tubules, producing mature sperm through meiosis and spermiogenesis.

Endocrine function: the gonads secrete sex steroids that regulate secondary sexual characteristics and reproductive cycles. Ovaries produce estrogens and progesterone; testes produce testosterone. Both gonads also secrete inhibins that modulate FSH secretion. The activity of the gonads is governed by the hypothalamic-pituitary-gonadal axis, with GnRH stimulating FSH and LH, which in turn regulate gametogenesis and hormone production.

Clinical note: gonadal development and function can be affected by genetic conditions, injuries, or diseases leading to disorders such as hypogonadism or gonadal dysgenesis. The study of gonads integrates anatomy, embryology, endocrinology, and clinical medicine.