Gonads : Testis and Overies

Gonads:

Both testes and ovaries, in addition to their role as reproductive gamete producing organs, function as endocrine structures also.

Testis

The testis in males, in addition to the germinal epithelial cells, contains groups of epithelioid cells called the interstitial or leydig cells. These cells constitute the endocrine tissue of the testis. The leydig cells secrete the androgenic hormone testosterone. The androgens are C19 steroids. In the normal post pubertal males, the rate of secretion of testosterone ranges from 4-9 mg per day.

Action of testosterone:

1.  Testosterone causes embryonic development of male reproductive organs,

2.                It promotes the development of the secondary sexual characters of males, including physical development, hair distribution, masculine voice and male behaviour at puberty.

Ovary

The ovaries are paired, oblong in shape and situated in the pelvic portion of the abdominal cavity. It releases hormones such asoestrogen and progesterone.

1. Oestrogen

Under the influence of the FSH from the adenohypophysis, the ovum grows and becomes enclosed in the Graffian follicle. Associated cells of the follicle produce a steroid hormone called estrogen. The oestrogens are C18 steroid compounds. It is responsible for the growth of female reproductive organs and for the appearance of secondary sexual characters.

2. Progesterone:

After the discharge of the ovum from the Graafian follicle and after fertilisation, the ruptured follicle cells form a new structure called corpus luteum. It produces the pregnancy hormone progesterone. Progesterone is also synthesized and secreted by the placenta during the later part of gestation. This hormone is a C-21 steroid compound.

Progesterone is responsible for the premenstrual growth in the non-pregnant woman's uterus. The development of the placenta during pregnancy and the embedding of the fertilized ovum in the uterus (implantation).

3. Relaxin:

The corpus luteum of the pregnant woman secretes another hormone, relaxin in addition to progesterone. Relaxin helps in relaxing the muscles and ligaments of pelvic organs during childbirth (parturition).