Male and Female Gonads

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Male and Female Gonads

Male and Female Gonads
Male Gonads (Testes) and Female Gonads (Ovaries). NIH Medical Arts/Alan Hoofring/Don Bliss/National Cancer Institute

What Are Gonads?

Gonads are the male and female primary reproductive organs. The male gonads are the testes and the female gonads are the ovaries. These reproductive system organs are necessary for sexual reproduction as they are responsible for the production of male and female gametes. Gonads also produce sex hormones needed for the growth and development of primary and secondary reproductive organs and structures.

Gonads and Sex Hormones

As a component of the endocrine system, both male and female gonads produce sex hormones. Male and female sex hormones are steroid hormones and as such, can pass through the cell membrane of their target cells to influence gene expression within cells. Gonadal hormone production is regulated by hormones secreted by the anterior pituitary in the brain. Hormones that stimulate the gonads to produce sex hormones are known as gonadotropins. The pituitary secretes the gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These protein hormones influence reproductive organs in various ways. LH stimulates the testes to secrete the sex hormone testosterone and the ovaries to secrete progesterone and estrogens. FSH aids in the maturation of ovarian follicles (sacs containing ova) in females and sperm production in males.

  • Female Gonad Hormones

    The primary hormones of the ovaries are estrogens and progesterone.

    Estrogens - Group of female sex hormones important for reproduction and the development of female sex characteristics. Estrogens are responsible for growth and maturation of the uterus and vagina; breast development; widening of the pelvis; greater fat distribution in the hips, thighs, and breast; uterus changes during the menstrual cycle; and increased growth of body hair.

    Progesterone - Hormone that functions to prepare the uterus for conception; regulates uterus changes during the menstrual cycle; increases sexual desire; aids in ovulation; and stimulates gland development for milk production during pregnancy.

    Androstenedione - Androgen hormone that serves as a precursor to testosterone and estrogens.

    Activin - Hormone that stimulates the production and release of follicle-stimulating hormone (FSH). It also assists in menstrual cycle regulation.

    Inhibin - Hormone that inhibits the production and release of FSH.
     

  • Male Gonad Hormones

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

    Testosterone - Sex hormone important for the development of male sex organs and sex characteristics. Testosterone is responsible for increased muscle and bone mass; increased growth of body hair; development of broad shoulders; deepening of the voice; and growth of the penis.

    Androstenedione - Hormone that serves as a precursor to testosterone and estrogens.

    Inhibin - Hormone that inhibits the release of FSH and is thought to be involved in sperm cell development and regulation.
     

Gonads: Hormonal Regulation

Sex hormones may be regulated by other hormones, by glands and organs, and by a negative feedback mechanism. Hormones that regulate the release of other hormones are called tropic hormones. Gonadotropins are tropic hormones that regulate the release of sex hormones by gonads. The majority of tropic hormones and the gonadotropins FSH and LH are secreted by the anterior pituitary. Gonadotropin secretion is itself regulated by the tropic hormone gonadotropin-releasing hormone (GnRH), which is produced by the hypothalamus. GnRH released from the hypothalamus stimulates the pituitary to release the gonadotropins FSH and LH. FSH and LH in turn stimulate the gonads to produce and secrete sex hormones.

The regulation of sex hormone production and secretion is also an example of a negative feedback loop. In negative feedback regulation, the initial stimulus is reduced by the response it provokes. The response eliminates the initial stimulus and the pathway is halted. The release of GnRH stimulates the pituitary to release LH and FSH. LH and FSH stimulate the gonads to release testosterone or estrogen and progesterone. As these sex hormones circulate in the blood, their rising concentrations are detected by the hypothalamus and pituitary. The sex hormones help to inhibit the release of GnRH, LH, and FSH, which results in decreased sex hormone production and secretion.

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Male and Female Gonads

Sperm Production
Colored scanning electron micrograph (SEM) of sperm cells (spermatozoa) in the seminiferous tubules of the testis. This is the site of spermatogenesis (sperm production). Each sperm cell consists of a head (green), which contains the genetic material that fertilizes the female egg cell, and a tail (blue), which propels the sperm. The heads of the sperm are buried in Sertoli cells (yellow and orange), which nourish the developing sperm. SUSUMU NISHINAGA/Science Photo Library/Getty Images

Gonads and Gamete Production

Gonads are where 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 one half the number of chromosomes as the parent cell. Haploid male and female sex cells unite during fertilization to become one diploid cell called a zygote. Hundreds of millions of sperm must be released in order for fertilization to take place.

Oogenesis (ovum development) occurs in the female ovaries. After meiosis I is complete, the oocyte (egg cell) is called a secondary oocyte. The haploid secondary oocyte will only complete the second meiotic stage if it encounters a sperm cell and fertilization begins. Once fertilization is initiated, the secondary oocyte completes meiosis II and is then called an ovum. When fertilization is complete, the united sperm and ovum become a zygote. A zygote is a cell that is at the earliest stage of embryonic development. A woman will continue produce eggs until menopause. At menopause, there is a decrease in the production of hormones that stimulate ovulation. This is a normally occurring process that happens as women mature, usually over age 50.

Gonadal Disorders

Gonadal disorders occur as a result of a disruption in the structure of function of male or female gonads. Disorders that impact the ovaries include ovarian cancer, ovarian cysts, and ovarian torsion. Female gonadal disorders associated with endocrine system hormones include polycystic ovary syndrome (results from a hormone imbalance) and amenorrhea (no menstrual period). Disorders of the male testicles include testicular torsion (twisting of the spermatic cord), testicular cancer, epididymitis (inflammation of the epididymis), and hypogonadism (testicles do not produce enough testosterone).

Sources:

  • SEER Training Modules, Introduction to the Endocrine System. U. S. National Institutes of Health, National Cancer Institute. Accessed 21 October 2013. http://training.seer.cancer.gov/anatomy/endocrine/
  • SEER Training Modules, Introduction to the Reproductive System. U. S. National Institutes of Health, National Cancer Institute. Accessed 24 January 2014. http://training.seer.cancer.gov/anatomy/reproductive/