Gonads: Origin, Structure and Disorders

In this article we will discuss about:- 1. Origin of Gonads 2. Structure and Location of Gonads 3. Disorders.

Origin of Gonads:

They develop from the mesoderm of the embryo. The gonads are the sex glands; the ovaries and the testes. They produce ova and sperms respectively but also secrete hormones.

Structure and Location of Gonads:

(a) Ovaries:

In the female the ovaries are located in the pelvic cavity in close proximity to the oviducts and the uterus. The hormones produced by the ovaries include oestrogens, progesterone, relaxin and inhibin/actin.

(i) Oestrogens:

These are secreted by the cells of Graafian (ovarian) follicles. Estradiol is the principal feminizing oestrogen. It stimulates the development of female secondary sex characteristics during puberty and maintains them through the reproductive years of adult life. It also stimulates maturation of ova (in the ovaries) and development of the uterine epithelium and the mammary glands.

(ii) Progesterone:

It is secreted by the corpus luteum of the ovary. It stimulates further development of the uterine epithelium and mammary glands. It is also required for the formation of the placenta and for the maintenance of pregnancy. Both estradiol and progesterone are required for ovulation.

(iii) Relaxin:

It is secreted by the corpus luteum only during the later stages of pregnancy and helps to soften ligaments, especially those that hold the pubic symphysis together. It may also affect other ligaments, e.g., if it affects a woman’s foot ligaments, she may experience an increase in shoe size following pregnancy.

(iv) Inhibin/Actin:

Inhibin/actin is secreted by the corpus luteum. Inhibin hormone inhibits and actin hormone activates the FSH and GnRH production.

(b) Testes:

A pair of testes is situated in the scrotum of male. The connective tissue present between the seminiferous tubules in a testis contains small clusters of endocrine cells called interstitial cells or Leydig’s cells. These cells secrete various male sex hormones called androgens. The principal androgen is testosterone.

(i) Functions of Testosterone:

(a) It stimulates the growth and development of male secondary sex organs like the seminal vesicles, prostate and penis. It also helps to maintain their normal functions. Because these organs do not produce gametes (sperms) and only help in reproduction are, therefore, called secondary sex organs.

(b) This hormone also stimulates the development of the male secondary sexual char­acters like beard, moustache and low-pitch male voice in man.

(c) Testosterone also stimulates the formation of sperms in the seminiferous tubules of the testes.

(d) This hormone promotes the growth of many body tissues such as bones and muscles.

It is due to this fact that male has a higher stature than the female.

(ii) Function of inhibin/Actin:

Inhibin/actin is secreted by the sustentacular cells of the seminiferous tubules of the testes. Inhibin hormone inhibits and actin hormone activates the FSH production from anterior lobe of pituitary gland.

Disorders of Gonads:

Hypogonadism:

Inadequate gonadal function is called hypogonadism. It is due to defects in, or injury to the hypothalamus, the pituitary gland, or the testes or ovaries. It includes male hypogonadism and female hypogonadism.

(a) Male Hypogonadism:

It is due to the deficiency of androgens— male sex hormones (hypo function of Leydig’s cells), deficiency of sperm formation (hypo function of Sertoli cells) or both, before puberty. As a result male secondary sexual characters and musculature do not develop.

(b) Female Hypogonadism:

It is due to deficiency of oestrogens (female sex hor­mones) pituitary gonadotropins (LH, FSH or both) or can represent primary ovary failure. It results in the lack of development of female secondary sexual characters.

Precocious Puberty:

Early maturation of ovaries and testes with production of ova before the age of 9 years in girls or sperms before 10 years in boys is called sexual precocity. The causes of sexual pseudo precocity are excess of sex hormones from the adrenal cortex, testes, ovaries or from other sources, including extra gonadal tumours.

(a) Sexual pseudo precocity in boys:

It occurs due to excess of testosterone produced by tumours of the testes or adrenal glands. Such boys are characterized by enlargement of penis, masculinization, early appearance of pubic and axillary hair, faster body growth, etc.

(b) Sexual pseudo precocity in girls:

It occurs due to excess of oestrogens secreted by tumours of ovaries and adrenal glands. Such girls are characterized by breast formation, early appearance of pubic hair. However, the maturation and discharge of ova do not occur.

Eunuchoidism:

Failure of testosterone secretion causes eunuchoidism.

A eunuch has:

(a) undeveloped and non-functional secondary sex organs like prostrate, seminal vesicles and penis,

(b) lacks external sex characters such as beard, moustache and low pitch voice and

(c) does not produce sperms.

Gynaecomastia (Gr. gyne- woman, mastos- breast):

Excessive development of male mammary glands is called gynaecomastia. Sometimes they secrete milk. It results when the secretion of oestrogens is more than androgens. In neonate (new born) and during puberty, gynaecomastia is caused by temporary increase in circulating oestrogens. Deficiency of testosterone in later life may also cause gynaecomastia.