Introduction Gonads are the organs of the body responsible for the formation of reproductive cells (sperms and ova). Thus, basically, gonads are reproductive organs. During reproduction, few cells of gonads also function as an endocrine gland and secrete some hormones. Both testes and ovary in addition to producing sperms and ova also produce hormones. These are known as sex hormones which are responsible for the appearance of secondary sexual characters. In man, they include the growth of hair on the face, chest, axillae and pubis and the masculine voice. In the woman, they include the development of the breasts, widening of the pelvis and sweet voice, no development of hair on the face. If sex glands are removed or do not function properly secondary sexual characters of either sex are suppressed, generally, females on the removal of ovaries develop male characters.
Testes or male gonads
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The testes of man are found inside a scrotal sac situated outside the body. It is made up of a large number of seminiferous tubules. The connective tissue of testes contains the special type of cells called as interstitial cells or Leydig's cells. These cells are responsible for the secretion of male sex hormones. These sex hormones induce the development of secondary sexual characters in males. Development and maturity of the penis and seminiferous tubules is directly influenced by the testes.
Hormones of testes Testes produce testosterone and the androsterone collectively known as androgens, under the influence of Luteinizing hormone (LH) from the anterior lobe of Pituitary . The hormones of testosterone are as follows:
- Testosterone : Testosterone is a steroid hormone secreted by interstitial cells of Leydig's and also from Sertoli cells. Interstitial cells are not present in the testes of a child but they are present in the testes of newborn infants and also in the testes of adults after puberty. The production testosterone dwindles rapidly beyond the age of 40 and almost zero by the age of 80.
- Androsterone : Androsterone is also a fairly strong androgen secreted in the testes in the presence of FSH (Follicle stimulating hormone).
Functions of androgens The functions of androgen (testosterone and androsterone) are as follows:
- Androgen is required for the stimulation of the growth and development of secondary male sex organs. E.g. penis, scrotum, prostate gland, seminal vesicles, etc.
- Androgens are responsible for the stimulation and development of secondary sexual characters of the male. E.g. growth and development of hairs on face and chest, low pitch or masculine voice, etc.
- Androgens are responsible for spermatogenesis, maturation of sperms and prevention of degenerative changes in sex organs.
- The androgens are presumably responsible for the muscular strength of males as compared to that of the female.
- Androgens are responsible for the normal skin colour i.e., firm and flesh colour in the absence of androgens skin gets furrowed, soft and pale in colour.
- Recent findings have shown that sodium, potassium, inorganic phosphate, nitrogen and chloride ion metabolisms are androgen dependent.
- Androgens increase the secretions of the sebaceous glands.
- Attraction towards the person of opposite sex is also controlled by testosterone.
Irregularities of Male hormones Hypersecretion of testosterone or androsterone causes sexual prematurity in individuals. Secondary sexual characters also develop before the desired age.
On the other hand, if the hormone is secreted in insufficient quantity, the organs involved in sexual reproduction become less developed. Sexual maturity is also achieved at the late stage. The persons become sexually inert (Eunuchs) in case of acute deficiency of the hormone. If testes of a person are removed such person becomes strong physically because he does not lose energy in reproductive activities. Testes of oxen and male goats are removed to keep them strong and large sized.
Ovary or Female gonads
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In human female, two ovaries are found in the lower portion of the abdomen one in each side of the uterus. The main function of ovaries is the production of the egg. However, corpus luteum of ovaries are also involved in the secretion of certain hormones which are chemically similar to hormones secreted by the adrenal cortex. Following types of hormones are secreted by ovaries in females:
- Estrogen : Estrogen is secreted before ovulation by the theca-intema f the developing follicle and later, after ovulation, by the granulosa and theca-lutein cells. Estrogen is also secreted by the placenta in the pregnant woman. Estrogens are responsible for the development of secondary sexual characters of the female and for the development of female sexual organs from those of a child to adult after puberty. Estrogen is also responsible for the menstrual cycle. Lack of estrogen leads to the failure of the menstrual cycle and underdeveloped genital tracts. Estrogen increases water contents and thickness of the skin. As the age of female increases from starting reproductive age, there is a considerable decrease in the production of estrogen. At the stage of menopause, the secretion is completely ceased and henceforth ability of reproduction in the female ceases. Overproduction of the hormone causes sexual maturity at an early age. Secretion of estrogen is controlled by FSH and LH.
- Progesterone : Progesterone is a steroid hormone secreted by corpus-luteum, placenta and adrenal cortex. Progesterone and estrogens are also capable of inhibiting the actions of each other. The main function of progesterone is to prepare the uterus for the implantation of the fertilized ovum. Progesterone helps in the proliferation of alveoli of mammary glands in the development of the breast during pregnancy and inhibits contraction of the uterus. Deficiency of this hormone may lead to abortion. Due to the action of this enzyme, menstruation cycle is stopped after fertilization and implantation of the fertilized egg on the wall of the uterus. Formation of new follicles does not take place. If fertilization does not occur, the corpus luteum is destroyed and M.C. again starts within a month.
- Relaxin : Relaxin hormone softens the epiphysis of the pubic symphysis resulting the relaxation of pelvic ligaments during childbirth. Relaxin is secreted by ovaries, placenta and the cells of the uterus. Deficiency or lower level of progesterone and relaxin causes problems during pregnancy and childbirth. Milk is not produced by mammary glands. In contrast, high level of progesterone increases the size of breasts. If hypersecretion of relaxin occurs, abortion may happen.
Conclusion Gonads include both testes and ova which secrete many hormones in male and female. Gonads are reproductive organs as well as endocrine glands. Gonads are regulated by the pituitary gland which is also called the master gland.