The Gonads (testes in males, ovaries in females) perform closely related dual functions.

  1. Synthesize Sex hormones
  2. Produce Germ Cells

The steroid sex hormones (gonads secretions) are responsible for growth, development, maintenance and regulation of reproductive system. Sex hormones are essentially required for the development of germ cells.

Hormones of Gonads

Hormones of Gonads

The sex hormones are categorized into THREE groups:

  1. Androgens or male sex hormones which are C-19 steroids.
  2. Estrogens or female sex hormones which are C-18 steroids. Ring A of steroid nucleolus is phenolic in nature and is devoid of C-19 methyl group.
  3. Progesterone is a C-21 steroid produced during the luteal phase of menstrual cycle and also during pregnancy.

1. Androgen

The male sex hormones or Androgens (type of Gonads) are produced by the Leydig cells of the testes and to a minor excitement by the adrenal glands in both the sexes. Ovaries also produce small amounts of Androgens.

Biosynthesis of Androgens:

  • Cholesterol is the precursor for the synthesis of Androgens.
  • It is first converted to Pregnenolone which then forms Androstenedione by two pathways—either through progesterone or through 17-hydroxypregnenolone.
  • Testosterone is produced from Androstenedione. The production of Androgens is under the control of LH and FSH.

Active form of Androgen

  • The primary product of testes is testosterone. However, the active hormone in many tissues is not testosterone but its metabolite dihydro-testosterone (DHT).
  • Testosterone, on reduction by the enzyme 5′-reductase, forms DHT.
  • This conversion mostly occurs in the peripheral tissues.
  • Some workers consider testosterone as a pro-hormone and dihydrotestosterone, the more potent form as the hormone.

Physiological and biochemical functions of androgens:

1. Sex related physiological functions:

The androgens, primarily DHT and testosterone influences:

  • Growth, development and maintenance of male reproductive organs.
  •  Sexual differentiation and secondary sexual characteristics.
  • Spermatogenesis
  • Male pattern of aggressive behavior.

2. Biochemical functions:

Many specific biochemical effects of androgens that ultimately influence the physiological functions stated above are identified. Androgens are anabolic in nature.

  • Effects on protein metabolism: Androgens promote RNA synthesis (transcription) and Protein synthesis (translation); Androgens cause positive nitrogen balance and increase the muscle mass.
  • Effects on carbohydrate and fat metabolisms: Androgens increase glycolysis, fatty acid synthesis and citric acid cycle.
  • Effects on mineral metabolism: Androgens promote mineral deposition and bone growth before the closure of epiphyseal cartilage.

2. Estrogen

Estrogens are predominantly ovarian hormones, synthesized by the follicles and corpus luteum of ovary. These hormones are responsible for maintenance of menstrual cycle and reproductive process in women.

Synthesis of Estrogens:

  • Estrogen synthesis occurs from the precursor cholesterol.
  • Estrogens are produced by spermatization (formation of aromatic ring) of androgens.
  • The ovary produces Estradiol (E2) and Estrone (E,) while the placenta synthesizes these two steroid hormones and Estridiol (E3).
  • The synthesis of Estrogens is under the control of LH and FSH

Physiological and biochemical functions of estrogens

1. Sex-related physiological functions: The Estrogens are primarily concerned with

  • Growth, development and maintenance of female reproductive organs.
  • Heart diseases in the women during repro­ductive age.
  • Maintenance of menstrual cycles.
  • Development of female sexual characteristics.

2. Biochemical functions : Estrogens are involved in many metabolic functions.

  • Lipogenic effect : Estrogens increase lipogenesis in adipose tissue and, for this reason; women have relatively more fat {about 5%)
  • Hypo-cholesterolemic effect: Estrogens lower the plasma total cholesterol. The LDL fraction of lipoproteins is decreased while the HDL fraction is increased. This explains the low incidence of atherosclerosis and coronary heart disease in the women during reproductive age.
  • Anabolic effect: Estrogens in general promote transcription and translation. The synthesis of many proteins in liver is elevated e.g. transferrin, ceruloplasmin.
  • Effect on bone growth: Estrogens like androgens promote calcification and bone growth. It is believed that decalcification of bone in the postmenopausal women leading to osteoporosis is due to lack of estrogens.
  • Effect on transhydrogenase : Transhydro-genase is an enzyme activated by estrogen. It is capable of transferring reducing equivalents from NADPH to NAD+. The NADH so formed can be oxidized. It is explained that in the women after menopause, due to deficiency of estrogens, the trans-hydrogenase activity is low. This results in the diversion of NADPH towards lipogenesis—causing obesity.

3. Progesterone

Progesterone is synthesized and secreted by corpus luteum and placenta. Progesterone, as of steroid hormones from cholesterol. LH controls the production of progesterone.

Biochemical functions of progesterone:

  1. Progesterone is essentially required for the implantation of fertilized ovum and maintenance of pregnancy.
  2. It promotes the growth of glandular tissue in uterus and mammary gland.
  3. Progesterone increases the body temperature by 0.5 to 1.5 F. the exact mechanism of this thermogenic effect is not clearly known. The measurement of temperature was used as an indicator for ovulation.

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