At about age 9 or so, a boy's central nervous system issues a message: "Change!" First, the hypothalamus gives off GnRH, a substance called gonadotropin-releasing hormone. Because this hormone is present in the hypothalamus even before puberty, it is thought that a protein named GPR54 helps get GnRH from the hypothalamus at the right time. When the GnRH arrives at the pituitary gland-a pea-sized gland at the base of your brain-the pituitary gland then produces two key hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Both of these hormones also exist before puberty, but after the pituitary is triggered by the hypothalamus, more of these hormones are created.
Early on in puberty, the hormones (which, along with hormones that begin development of the testes, are known as gonadotropins) are made only at night. In later stages of puberty, when growth speeds up, these hormones are being produced day and night and in greater and greater quantities.
When it reaches the testes, FSH spurs the growth of seminiferous tubules, channels in the testes where sperm is produced. Once these tubules form and the infrastructure is in place, the boy can begin producing sperm.
LH, on the other hand, has another function. It tells cells within the testes called Leydig cells to make androgens. Androgens are hormones affecting the development of a male's reproductive capability. Testosterone is the main androgen, although there are many others.
Between the period when FSH and LH first reach the testes and the period when a pubescent boy can successfully reproduce, growth of hair along with changes in penis length and width have occurred.
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