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. (Gonads)

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. (Gonads)

Ovary

The ovaries are paired, oblong in shape and situated in the pelvic
portion of the abdominal cavity. It releases hormones such as oestrogen
and progesterone. (Gonads)

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). (Gonads)

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). (Gonads)