Late Gonadal Reactions

Ovaries

The ovaries are located within the pelvis and are very sensitive to radiation. The critical cell is the oocyte, gametes which are halted in prophase I until selected for maturation during the menstrual cycle. Oocytes are highly sensitive to radiation and are killed in great numbers by only a small dose; they die through apoptosis.
Clinically, the late effects are dependent on the age of the woman. Pre-pubescent females may suffer from delayed puberty. Post-pubertal females may have infertility or early menopause. The menstrual cycle is dependent on the maturation of oocytes as follicles; with the absence of this menopause occurs. This may lead to symptoms of amenorrhoea, decreased libido, hot flushes and bone demineralisation.
The TD5/5 is 2-3 Gy for the development of infertility. The TD50/5 is 6 - 12 Gy. In general, younger women tolerate a higher dose due to increased numbers of oocytes. The dose is significantly lowered when concurrent alkylating agents are used.

Testes

Unlike the ovaries, the hormonal and gametic functions of the testis are performed by different mechanisms. The germinal epithelium of the seminepherous tubules contains Sertoli cells and spermatocytes; the spermatocytes mature into spermatozoa whereas the Sertoli cells support the developing cells and are involved in feedback regarding FSH to the hypothalamus. The stroma between the tubules contains Leydig cells, which secrete testosterone and are under control of lutenising hormone.
The epithelium of the seminepherous tubules is highly sensitive to radiation, similar to the oocytes of the ovary. Doses of 0.1 Gy lead to a reduction in sperm count, and 0.15 Gy lead to temporary azoospermia (sterility). The developing spermatocytes/spermatozoa are relatively resistant compared to the However, it is possible for the epithelium to regenerate after some time, unlike the oocytes of the ovary which are not replaced if lost. 2 Gy in a single dose leads to azoospermia for years; permanent azoospermia occurs after 6 - 8 Gy of conventional fractionation.
The Leydig cells are relatively resistant to radiation, and their function is unrelated to the production of spermatozoa. Therefore infertility does not lead to hormonal changes (as in women).

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