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15.8: Gonadal and Placental Hormones

  • Page ID
    22361
  • By the end of this section, you will be able to:

    • Identify the primary hormones produced by the testes and ovaries
    • Name the hormones produced by the placenta and state their functions

    This section briefly discusses the hormonal role of the gonads—the testes and ovaries—which produce the sex cells (sperm and ova, respectively) and secrete the gonadal hormones. The roles of the gonadotropins released from the anterior pituitary (FSH and LH/ICSH) were discussed earlier. The anatomy of these organs is covered in more detail in the Reproductive System chapter.

    The primary hormone produced by the testes is testosterone, a steroid hormone important in the development of the male reproductive system, the maturation of sperm cells, and the development of male secondary sex characteristics such as a deepened voice, body hair, and increased muscle mass. Interestingly, testosterone is also produced in the ovaries, but at a much reduced level. In addition, the testes produce the peptide hormone inhibin, which inhibits the secretion of FSH from the anterior pituitary gland. FSH stimulates spermatogenesis, or sperm cell production.

    The primary hormones produced by the ovaries are estrogens, which include estradiol, estriol, and estrone. Estrogens play an important role in a larger number of physiological processes, including the development of the female reproductive system, regulation of the menstrual cycle, the development of female secondary sex characteristics such as increased adipose tissue and the development of breast tissue, and the maintenance of pregnancy. Another significant ovarian hormone is progesterone, which contributes to regulation of the menstrual cycle and is important in preparing the body for pregnancy as well as maintaining pregnancy. In addition, the granulosa cells of the ovarian follicles produce inhibin, which—as in those with testes—inhibits the secretion of FSH. During the initial stages of pregnancy, an organ called the placenta develops within the uterus. The placenta supplies oxygen and nutrients to the fetus, excretes waste products, and produces and secretes estrogens and progesterone. The placenta produces human chorionic gonadotropin (hCG) as well. The hCG hormone promotes progesterone synthesis and reduces the mother’s immune function to protect the fetus from immune rejection. The hormones controlling reproduction are summarized in Table \(\PageIndex{1}\).

    Table \(\PageIndex{1}\): Reproductive Hormones
    Gonad Associated hormones Effect
    Testes Testosterone Stimulates development of male secondary sex characteristics and sperm production
    Testes Inhibin Inhibits FSH release from pituitary
    Ovaries Estrogens and progesterone Stimulate development of female secondary sex characteristics and prepare the body for childbirth
    Placenta Human chorionic gonadotropin Promotes progesterone synthesis during pregnancy and inhibits immune response against fetus

    EVERYDAY CONNECTIONS

    Anabolic Steroids

    The endocrine system can be exploited for illegal or unethical purposes. A prominent example of this is the use of steroid drugs by professional athletes.

    Commonly used for performance enhancement, anabolic steroids are synthetic versions of the sex hormone testosterone. By boosting natural levels of this hormone, athletes experience increased muscle mass. Synthetic versions of human growth hormone are also used to build muscle mass.

    The use of performance-enhancing drugs is banned by all major collegiate and professional sports organizations in the United States because they impart an unfair advantage to athletes who take them. In addition, the drugs can cause significant and dangerous side effects. For example, anabolic steroid use can increase cholesterol levels, raise blood pressure, and damage the liver. Altered testosterone levels (both too low or too high) have been implicated in causing structural damage to the heart, and increasing the risk for cardiac arrhythmias, heart attacks, congestive heart failure, and sudden death. Paradoxically, steroids can cause shriveled testes and enlarged breast tissue in men. In females, their use can cause analogous effects such as an enlarged clitoris and growth of facial hair. In both sexes, their use can promote increased aggression (commonly known as “roid-rage”), depression, sleep disturbances, severe acne, and infertility.

    Concept Review

    The reproductive system in both males and females is regulated by follicle-stimulating hormone (FSH) and luteinizing hormone (LH, also called interstitial cell stimulating hormone or ICSH in males) produced by the anterior lobe of the pituitary gland in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus. In males, FSH stimulates sperm maturation, which is inhibited by the hormone inhibin. The steroid hormone testosterone, a type of androgen, is released in response to ICSH and is responsible for the maturation and maintenance of the reproductive system, as well as the development of male secondary sex characteristics. In females, FSH promotes egg maturation and LH signals the secretion of sex hormones: estrogens and progesterone. Both of these hormones are important in the development and maintenance of the female reproductive system, as well as maintaining pregnancy. The placenta develops during early pregnancy, and secretes several hormones important for maintaining the pregnancy.

    Review Questions

    Q. The gonads primarily produce what class of hormones?

    A. amine hormones

    B. peptide hormones

    C. steroid hormones

    D. catecholamines

    Answer

    Answer: C

    Q. The production of FSH by the anterior pituitary is reduced by which hormone?

    A. estrogens

    B. progesterone

    C. testosterone

    D. inhibin

    Answer

    Answer: D

    Critical Thinking Questions

    Q. Compare and contrast the role of estrogens and progesterone.

    Answer

    A. Both estrogens and progesterone are steroid hormones produced by the ovaries that help regulate the menstrual cycle. Estrogens play an important role in the development of the reproductive tract and secondary sex characteristics in females. They also help maintain pregnancy. Progesterone prepares the body for pregnancy and helps maintain pregnancy.

    Glossary

    estrogens
    class of sex hormones important for the development and growth of the reproductive tract, secondary sex characteristics, and the reproductive cycle in females, and the maintenance of pregnancy
    inhibin
    hormone secreted by the gonads that inhibits FSH production by the anterior pituitary
    progesterone
    sex hormone important in regulating the reproductive cycle in those with ovaries and the maintenance of pregnancy
    testosterone
    steroid hormone secreted by the testes and important in the maturation of sperm cells, growth and development of the reproductive system, and the development of secondary sex characteristics in males

    Contributors and Attributions