Gonadotropins are critical hormones in the female menstrual cycle. They are usually influence by gonadotropin releasing hormone (GnRH) and their functions are influenced by their levels in the body. The levels of these hormones vary it course of the menstrual cycle and influence the ovaries to facilitate ovum development and ovulation.
The changes in the levels of gonadotropins have a significant influence on the ovary since they catalyze several processes in the ovary. High follicle-stimulating hormone (FSH) levels at the beginning of the preovulatory phase encourage the development of around 15-20 immature follicles inside the ovaries. The follicles release estrogen and androgens resulting in the rise in the levels of the sex steroid in the bloodstream during the preovulatory phase.
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A significant rise in the levels of the gonadotropin hormones occurs at the end of the preovulatory phase as the ovaries prepare for ovulation, making this point in the menstrual cycle the point when the hormones are at their highest levels (Henderson, 2020a). The increase arises because of the rise in GnRH which increases secretion of the gonadotropins increases.
The increase in gonadotropins encourages the remaining one follicle out of the 15-20 that were released earlier to expand in diameter to about 1inch (25 mm). The growth of the follicle signifies the maturation of the ovum in preparation for release during ovulation. The ovum maturation is primarily influenced by the follicle-stimulating hormone (FSH), one of the gonadotropins (Henderson, 2020b). As the follicle grows, it bulges on the ovary walls, and as ovulation starts, it breaks away, releasing an ovum alongside halo supporting cells. The ovulation is triggered by the luteinizing hormone (LH), which is the second gonadotropin hormone. LH further influences the ovary to release sex steroids estrogen, progestin, and androgens. As the ovum is released, the oviduct's fimbria reaches out and captures it, propelling it into the oviduct through the waving of cilia.
In males, the gonadotropins play different roles than they do in females. However, in male, the levels of these hormones stay fairly stable. If the levels of gonadotropins in males increase, there will be negative feedback in the pituitary and hypothalamus caused by increased inhibin and testosterone levels. The negative feedback encourages the pituitary and hypothalamus to reduce the manufacture of gonadotropins. The increase and decrease in the levels of these hones in male is influenced by the male HPG axis.
HPG axis in men involves an intricate collaboration of the hypothalamus, pituitary gland, and gonads. The glands and organs perform various functions to facilitating the function of the axis (Fasano, Cobellis, Pierantoni, & Meccariello, 2014). The hypothalamus usually discharges GnRH, which goes to the pituitary glands anterior lobe, binding the glands receptors. As a result, LH and FC are released and travel via the bloodstream to the gonads (testicles). Once in the testicles, LH encourages testicles' Leydig cells to generate testosterone, to facilitate spermatogenesis. FSH acts on the Sertoli cells, stimulating them to generate androgen binding globulin (ABG) and inhibin. The ABG usually binds to testosterone to prevent it from exiting from the seminiferous tubules. In contrast, inhibin supports the spermatogenesis process while inhibiting the production of GnRH, LH, and FSH (Fasano et al., 2014). Once the levels of inhibin and testosterone go beyond the optimum levels, they have negative feedback on the hypothalamus and pituitary glands and thus decree the creation of LH and FSH, subsequently controlling the elves of inhibin and testosterone.
If high levels of LH in a male are not corrected by the negative feedback mechanism, it causes overproduction of testosterone and may affect fertility by reducing sperm production. Similarly, an unregulated high level of FSH may be an indication of a dysfunctional testis, and the man becomes infertile.
References
Fasano, S., Cobellis, G., Pierantoni, R., & Meccariello, R. (2014). Modulators of hypothalamic-pituitary-gonadal axis for the control of spermatogenesis and sperm quality in vertebrates . Frontiers E-books
Henderson, K. (2020a, February 17). Menstrual Cycle. YouTube . https://www.youtube.com/watch?v=o5rC0vPNTXA&feature=youtu.be
Henderson, K. (2020b, February 17). Female Endocrinology. YouTube . https://www.youtube.com/watch?v=UPOKfr9EmUU&feature=youtu.be
