If the sperm count reaches 20 million/ml, the Sertoli cells stop secreting inhibin, and stops negative feedback which initiates spermatogenesis once again. The products of Leydig cells and Sertoli cells are summarized in the table below. In endocrine control, activin will activate (more testosterone production) and inhibin will inhibit (less testosterone production). In paracrine control, activin will inhibit (less testosterone production) and inhibin will activate (more testosterone production). Consequently, there has to be some type of communication between germ cells and Sertoli cells that allows for the coordinated movement of sperm between compartments. As we discussed previously, sperm will mature in ‘waves’ and are produced between the space of two adjacent Sertoli cells. A growth spurt occurs toward the end of puberty, at approximately age 11 to 13, and height can increase as much as 4 inches a year. An increased production of testosterone leads to growth of the testes, typically the first physical sign of the beginning of puberty, which is followed by growth and pigmentation of the scrotum and growth of the penis. An increased production of estrogen at puberty typically leads to the development of breast tissue. Pubic hair may extend out to their thighs, and some boys may have a line of hair up to their belly button. Many may not develop facial hair until this step in the process. It’s most common between the ages of 11 and 15 years. But it typically resolves by the end of puberty. In this stage, boys haven’t experienced any visible changes, but their adrenal glands are maturing. For parents, the Tanner stages can serve as an excellent guide to the changes you can expect to see in your son. Most girls reach their peak height by age 16, but some may continue growing through age 20. Free testosterone (T) is transported into the cytoplasm of target tissue cells, where it can bind to the androgen receptor, or can be reduced to 5α-dihydrotestosterone (5α-DHT) by the cytoplasmic enzyme 5α-reductase. This additional information could suggest, contrarily, that testosterone may encourage greed or selfishness. Moreover, the conversion of testosterone to estradiol regulates male aggression in sparrows during breeding season. A few studies indicate that the testosterone derivative estradiol might play an important role in male aggression. The Annals of the New York Academy of Sciences has found that the use of anabolic steroids (which increases testosterone) among teenagers is correlated with increased likelihood of using violence. It is therefore the challenge of competition among males that facilitates aggression and violence. There has been speculation that these changes in testosterone result in the temporary reduction of differences in behavior between the sexes. FSH and LH affect reproductive structures to cause the formation of sperm and the preparation of eggs for release and possible fertilization. Reproductive endocrinologists undergo extensive medical training, first in a four-year residency in obstetrics and gynecology, then in a three-year fellowship in reproductive endocrinology. Doctors may use fertility drugs, surgery, or assisted reproductive techniques (ART) in their therapy. A reproductive endocrinologist is a physician who treats a variety of hormonal disorders related to reproduction and infertility in both men and women. Estrogen is involved in calcium metabolism and, without it, blood levels of calcium decrease. The endometrium begins to degenerate as the progesterone levels drop, initiating the next menstrual cycle. The level of estrogen produced by the corpus luteum increases to a steady level for the next few days. As depicted in figure 3, rising levels of testosterone act on the hypothalamus and anterior pituitary to inhibit the release of GnRH, FSH, and LH. LH acts on Leydig cells to stimulate the production of testosterone and androgens. FSH acts on Sertoli cells to stimulate the production of inhibin, growth factors, activin and follistatin. Although this pathway has not been explicitly identified, there must be a mechanism where germ cells provide updates to Sertoli cells on maturation stage. In this pathway, positive feedback onto Leydig cells will produce more testosterone, whereas negative feedback will stop testosterone production. For men with low blood testosterone levels and symptoms most likely caused by a low level, the benefits of hormone replacement therapy usually outweigh potential risks. Testosterone therapy is approved for the treatment of delayed male puberty and abnormally low production of testosterone secondary to malfunction of the testes, pituitary or hypothalamus. Estrogen therapy increases sex hormone binding globulin and, like aging men, this reduces the amount of free, active testosterone in the body. One treatment available for many of these problems is spironolactone, a special type of diuretic (water pill) that blocks the action of male sex hormones. It is essential to the development of male growth and masculine characteristics. During puberty, children who are genetically male with 5-alpha reductase deficiency experience a lack of facial hair growth. This causes them to not have secondary sexual characteristics and to have infertility.
