Gonadas: What are they? Sex Hormones, Glands, Development, Estrogen, Progesterone and Associated Disorders

They are the primary male and female reproductive organs. The male gonads are the testicles, and the female gonads are the ovaries.

These organs of the reproductive system are necessary for sexual reproduction since they are responsible for producing male and female gametes.

The gonads also produce sex hormones necessary to grow and develop primary and secondary reproductive organs and structures.

Gonads and sex hormones

The male and female gonads produce sex hormones as a component of the endocrine system.

The male and female sex hormones are steroid hormones and, as such, can cross the cell membrane of their target cells to influence gene expression within cells.

The gonadal hormone production is regulated by hormones secreted by the anterior pituitary gland in the brain.

The hormones that stimulate the gonads to produce sex hormones are called gonadotropins. The hypophysis secretes the luteinizing hormone gonadotropins (LH) and the follicle-stimulating hormone (FSH). These protein hormones influence the reproductive organs in several ways.


Luteinizing hormone stimulates the testes to secrete the sex hormone testosterone and the ovaries to secrete progesterone and estrogen. FSH helps in the maturation of ovarian follicles (sacs containing ovules) in females and the production of sperm in males.

Male and female gonads

The gonads in men are the testicles, and the gonads in women are the ovaries. Each has a role played in the endocrine system by the male and female gonads.

Key points:

The ovary is an ovule reproductive organ, often found in pairs as part of the vertebrate female reproductive system.

The ovaries secrete estrogen and progesterone, and also androgens such as testosterone.

The testicle is the male reproductive gonad in humans.

The main functions of the testicles are to produce sperm (spermatogenesis) and produce androgens, mainly testosterone.

The functions of the testicle are influenced by the gonadotropic hormones produced by the anterior pituitary gland.

Both testosterone and follicle-stimulating hormone are necessary to support spermatogenesis.

Gonad: a sexual organ that produces gametes, specifically, the testicles or ovaries.

Testicles: the male gonads responsible for the production of sperm and the secretion of testosterone.

Ovaries: the female gonads responsible for the production of ovules and the secretion of essential hormones.

Gonads and the sex glands

The gonads are the ovaries in the female, which produce eggs (ova), and the testicles in the male, which produce sperm. Both also produce sex hormones. Glands that produce sex hormones and reproductive cells: testicles in the male, ovaries in the female.

The development of the gonad, the determination of sex, and the reproductive success of offspring depend largely on sex hormone systems. The developing organism is exquisitely sensitive to alterations in hormonal function.

In the early embryonic state, the gonads of males and human females are morphologically identical.

Sexual differentiation begins under the hormonal influence during the fifth and sixth weeks of fetal development, and therefore, altering hormones during this susceptible period can have profound consequences.

Development of the indifferent gonad

The gonads develop from the intermediate mesoderm located in the paired longitudinal urogenital crests, the medial part of these crests being the gonadal ridges.

In the sixth week, the primordial germ cells migrate from the yolk sac wall through the dorsal mesentery of the hindgut to occupy the gonadal crests. These cells’ arrival induces the crests’ cells to form primitive sexual cords (derived from the mesonephros and the superposed coelomic epithelium).

The gonad is indifferent or uncommitted at this stage and consists of an outer cortex and an internal medulla. During the next week, the male and female gonads begin to differentiate. If the germ cells do not migrate to the gonadal ridges, the gonads do not develop.

The gonads are derived from the intermediate mesoderm. At 4 to 6 weeks of gestation in humans, the urogenital ridges develop as even excrescences of the coelomic epithelium (mesothelium). The gonads, the adrenal cortex, the kidney, and the reproductive tract are derived from the urogenital crest.

Several genes are necessary for the development of the bipotential gonad. The Wilms tumor gene (WT1) encodes a zinc transcription factor expressed in embryonic mesodermal tissues and appears to influence mesodermal-epithelial interactions.

GATA4 is expressed in the somatic cells of the urogenital crest and the bipotential gonad before displaying the specific expression of sex. Chromobox homolog 2 (CBX2) appears to play a role in early gonadal development and may promote transactivation of steroidogenic factor 1 (NR5A1), which NR5A1 / SF1 encodes.

NR5A1 is expressed in the urogenital crest and appears to upregulate the SRY expression. In addition to transcription factors and specific secreted factors (hormones), physical contact with the mesonephros appears essential for later gonadal differentiation.

Due to its origin as part of the developing urogenital system, the ovaries and testes are located initially in the upper abdomen, near the kidneys.

One of the first morphological changes is the increased proliferation and size of gonads 46, XY in development. The bipotential gonad consists of at least four cell lineages: germ cells, support cells, steroidogenic cells, and connective tissue.

Although the determination of sex has been equated with the differentiation of the testicle, recent data question this dogma. In contrast, specific signaling molecules activate or repress the gonadal determination for the testes and ovaries.

The competition between specific genes and proteins influences cell fate decisions in gonadal development.

Estrogen and progesterone

The gonad is the organ that makes the gametes. The gonads in men are the testicles, and the gonads in women are the ovaries. Both gonads in men and women are endocrine glands.

Gonads and female hormones

The primary hormones of the ovaries are estrogen and progesterone.

Estrogens: a group of female sex hormones necessary for reproducing and developing female sexual characteristics.

Estrogens are responsible for the growth and maturation of the uterus and vagina, the breasts’ development, the pelvis’s widening, and more excellent distribution of fat in the hips, thighs, and chest—the uterus changes during the menstrual cycle and further growth of the body hair.

Progesterone: a hormone that works to prepare the uterus for conception, regulates changes in the uterus during the menstrual cycle, increases sexual desire, helps in ovulation, and stimulates the development of glands for milk production during pregnancy.

Androstenedione is an androgenic hormone that is a precursor to testosterone and estrogen.

Activin is a hormone that stimulates follicle-stimulating hormone (FSH) production and release. It also helps in regulating the menstrual cycle.

Inhibin: a hormone that inhibits the production and release of the follicle-stimulating hormone.

Gonads and male hormones

Androgens are hormones that mainly influence the development of the male reproductive system. Although they are found at much higher levels in men, androgens are also produced in women. Testosterone is the primary androgen secreted by the testes.

Testosterone: is an important sex hormone for developing male sexual organs and sexual characteristics. Testosterone is responsible for increasing muscle and bone mass, increasing body hair growth, developing broad shoulders, deepening the voice, and growth of the penis.

Androstenedione: a hormone that serves as a precursor to testosterone and estrogen.

Inhibin: a hormone that inhibits the release of the follicle-stimulating hormone and is believed to be involved in developing and regulating sperm cells.

Gonads and hormonal regulation

Sex hormones can be regulated by other hormones, glands, organs, and a negative feedback mechanism. The hormones that regulate the release of other hormones are called low hormones.

Gonadotropins are low hormones that regulate the release of sex hormones by the gonads. The anterior pituitary secretes most of the tropical and follicle-stimulating hormones gonadotropins and luteinizing hormones.

Gonadotropin secretion is regulated by the hormone low hormone gonadotropin-releasing hormone (GnRH), produced by the hypothalamus.

The gonadotropin-releasing hormone released from the hypothalamus stimulates the pituitary to release the follicle-stimulating hormone gonadotropins and luteinizing hormone.

The follicle-stimulating hormone and luteinizing hormone, in turn, stimulate the gonads to produce and secrete sex hormones.

The regulation of the production and secretion of sex hormones is also an example of a negative feedback cycle. In the negative feedback regulation, the initial stimulus is reduced by its provoking response.

The response eliminates the initial stimulus, and the path stops. Gonadotropin-releasing hormone releases the pituitary gland to release luteinizing and follicle-stimulating hormones.

Luteinizing and follicle-stimulating hormones stimulate the gonads to release testosterone, estrogen, and progesterone.

As these sex hormones circulating in the blood, the hypothalamus and pituitary gland detect increasing concentrations.

The sex hormones help inhibit the release of gonadotropin-releasing hormone, luteinizing hormone, and follicle-stimulating hormone, decreasing the production and secretion of sex hormones.

Gonads and gamete production

The gonads are where the male and female gametes are produced. The production of sperm cells is known as spermatogenesis. This process occurs continuously and takes place within the male testes.

The male germ cell or spermatocyte undergoes a two-part cell division process called meiosis. Meiosis produces sex cells with half the number of chromosomes that the parent cell.

The male and female haploid sex cells unite during fertilization to become a diploid cell called a zygote. Hundreds of millions of sperm must be released for fertilization to take place.

Oogenesis (egg development) occurs in the female ovaries. After meiosis I is completed, the oocyte (ovum) is called a secondary oocyte. The haploid secondary oocyte will only complete the second meiotic stage if it finds a sperm cell and fertilization begins.

Once fertilization begins, the secondary oocyte completes meiosis II and is called an ovum. When fertilization is complete, the bound sperm and egg become a zygote.

zygote is a cell in the earliest stage of embryonic development. A woman will continue to produce eggs until menopause.

During menopause, there is a decrease in the production of hormones that stimulate ovulation. This process usually occurs when women mature, usually older than 50 years.

Gonadal disorders

Gonadal disorders occur due to an interruption in the structure of the function of the male or female gonads. Disorders that affect the ovaries include ovarian cancer, cysts, and ovarian torsion.

Female gonadal disorders associated with hormones of the endocrine system include polycystic ovarian syndrome (results of hormonal imbalance) and amenorrhea (without a menstrual period).

Disorders of the male testes include

  • testicular torsion (torsion of the spermatic cord),
  • testicular cancer,
  • epididymitis (inflammation of the epididymis), and
  • hypogonadism (the testes do not produce enough testosterone).