Gonadal Hormones

Human Physiology

Lesson 39 : Adrenal, Gonads & Placenta

Gonadal Hormones

Gonads (Ovaries & Testes) produces different steroid hormones required for development of reproductive organs and other conditions favourable for fertilization and pregnancy. Important gonadal steroids are:

  • Estrogen & progesterone from ovaries.
  • Testosterone. from testes
  • Estrogens: comprises of estradiol, estriol and estrone. These hormones are produced during first half of menstrual cycle from the developing follicles and performs following functions:
    • Growth of female reproductive tract.
    • Development of secondary sex characters.
    • Growth of mammary glands.
    • Development of female sex behaviour.

    Secretion of estrogen is stimulated by FSH hormone from anterior pituitary which is influenced by negative feed back of estrogens.

    • Progesterone: is produced during second half of menstrual cycle from corpus luteum. Progesterone is required for following functions:
      • Relaxation of uterus for pregnancy.
      • Growth of mammary glands.
      • Implantation of embryo.

      Progesterone secretion is stimulated by pituitary LH hormone which is further controlled by negative feed back mechanism.

    • Testosterone : The hormone is also termed as androgen and is secreted from testes in more or less in uniform pattern. The hormone is physiologically required for following activities:
      • Development of male genital tract.
      • Development of secondary male characters.
      • Development of male sex behaviour.

      Secretion testosterone is stimulated by LH from anterior pituitary.

      Placenta As Endocrine Organ

      Placenta is composite organ comprising of fetal and maternal tissue required for protection, supply of oxygen and nourishment of developing embryo & fetus. Apart from these actions it also produces several hormones some of which are:

      1. Chorionic gonadotropins (hCG): is a protein hormone produced during 30-150 days of pregnancy from fetal chorionic cells of placenta. Functionally it is similar to LH hormone of anterior pituitary and its physiological significance is:
        • Maintenance of corpus luteum during early pregnancy and promotes progesterone secretion.
        • Inhibition of release of FSH from anterior pituitary through progesterone, thereby preventing follicular development on ovaries and occurrence of menstrual cycle during pregnancy.
        • Secretion of HCG in urine forms the basis urine pregnancy test in pregnant women.
      2. Placental Steroids: Both estrogen and progesterone are produced from placenta and helps in continuation of pregnancy during 2nd and last trimester when ovaries are unable to produce required quantity of steroids.
      3. Placental Lactogen: This is a protein hormone with similar structure as that of prolactin and growth hormone. It is important for fetal growth as well as for prepares mammary glands for lactation.
      Prostaglandin Hormones(PG)

      PG are also known as local hormones released from variety of cells such as lining cells of blood vessels, leucocytes, platelets and tissue cells. PG do not travel to distant organs through blood rather acts in vicinity of organs. PGs have several chemical derivatives such as PGA, PGE, PGF etc which are synthesized from common precursor called arachidonic acid (a 20 carbon polyunsaturated fatty acid). Some important functions of PG are:

      • Increase motility in gastro intestinal tract and decreases gastric acid secretion.
      • Increase motility of sperms & ova in reproductive tract.
      • In kidney PG improve circulation and inhibit action of ADH.
      • PGs are related with body temperature regulation and they induce inflammation in injured tissue.

      Hormones acting as internal secretions of endocrine glands are involved in maintenance of many body functions like metabolism of nutrients (insulin, glucagons, corticosteroids and adrenaline), water and electrolyte homeostasis (aldosterone and ADH), tissue growth (growth hormone, prolactin, insulin and sex steroids), reproductive process (FSH, LH, sex steroids) and temperature regulation (thyroxine, prostaglandin) etc. The deficiency of hormone results in disease which can be treated with supplementation of deficient hormone.

Last modified: Wednesday, 11 April 2012, 4:54 AM