|MadSci Network: Development|
Steven: The onset of puberty is dependent upon the hypothalamus-pituitary-gonadal axis shifting its function to secrete hormones in the appropriate pattern. Each level must be competent to 1) do its own job & 2) respond to signalling from the other glands/organs. For example, at the onset of puberty, the total amount of gonadotropin-releasing hormone secretion from the hypothalamus (an area in the brain) increases. This signals the pituitary gland (located just inferior to the hypothalamus) to secrete more luteinizing and follicle-stimulating hormone. These hormones signal the ovaries to increase their function so that steroids can be produced and eggs are prepared for ovulation. The ovarian steroids must complete the cycle and communicate how things are going at the ovary to the hypothalamus and pituitary. This cyclic relationship must be balanced in order for normal function to continue. The largest single reason for decreased age of menarche is improved nutrition. As the level of nutrition increases, the bodies ability to store energy as fat increases. It has been shown in ewe lambs that there is a target body weigth must be reached in order for estrous cycles to begin. If the lamb is held at lower weight, there will be a delay in onset. It can be inferred that this phenomenon may occur in humans as well. Improvements in disease prevention and control also contributes to the overall health of the human population, therefore, contributing to enhanced reproductive function. The human population has become much more mobile in the past two centuries. This provides the opportunity for gene pool mixing and increasing the opportunity for increasing the variability within the gene pool. Thus, providing for the opportunity for enhanced biology. I hope this helps. David Mallory, PhD Associate Professor Department of Biological Sciences Marshall University Huntington, WV
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