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Male Reproductive System

Male Sex Hormones and Puberty

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) produced by the anterior pituitary gland and testosterone produced by the testes are the three principle hormones affecting the male reproductive system.

Hormones are chemicals that are produced by endocrine glands in the body. These substances are released into the extracellular fluid, where they diffuse into the bloodstream. Hormones regulate the physiological control of various organs and tissues. In males there are three primary hormones involved in male reproduction and characteristics—testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). Testosterone is the sex hormone that signals the development of male sex organs and contributes to specific secondary sexual characteristics in males. Testosterone is derived from cholesterol, a lipid. It circulates as a prohormone that can be used to make a hormone called dihydrotestosterone. This conversion to dihydrotestosterone takes place in tissues of the testes, prostate gland, and muscles and is necessary to help develop the penis and scrotum during fetal development.

FSH and LH are both gonadotropins, hormones that stimulate activity of gonads. A gonad is a reproductive organ that produces gametes and sex hormones. Release of FSH and LH is regulated by the hypothalamus. The hypothalamus (the brain region responsible for regulating many involuntary body functions) releases gonadotropin-releasing hormone (GnRH) that stimulates the release of FSH and LH from the anterior pituitary gland. If testosterone levels exceed their normal range, testosterone has an inhibitory effect on the hypothalamus and anterior pituitary gland, reducing the release of GnRH and LH and signaling the interstitial endocrine cells to stop testosterone production.

Sperm production is also controlled by a negative feedback system. When large numbers of sperm are present in the testes, the sustentocytes in the testes release the hormone inhibin. Inhibin has an inhibitory effect on the hypothalamus and anterior pituitary. Consequently GnRH, FSH, and LH secretions decline and sperm production falls.

Male Sex Hormone Regulation

The hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Both act on the testes to increase sperm production (FSH) and stimulate testosterone production (LH), processes regulated by negative feedback.
Puberty is the developmental stage characterized by sexual maturation. In males, it begins between the ages of 10 and 12 and ends around age 14 when functional, viable sperm are produced. At the onset of puberty, a large volume of GnRH is released from the hypothalamus, which results in increased FSH and LH levels. LH stimulates interstitial cells of the testes to secrete testosterone. FSH stimulates sperm production by prompting sustentocytes of the testes to release androgen-binding protein, which keeps testosterone concentrations high. This high level of testosterone stimulates the process of spermatogenesis (production of sperm). High levels of testosterone and dihydrotestosterone also encourage the development of male sexual characteristics. These include an enlargement of the penis and testes, an increase in muscle and bone growth, widening of the jaw and shoulders, a deep voice from larynx enlargement, an increase in facial and body hair production, an increase in sexual drive, and an increase in erections.

Stages of Puberty in Males

Puberty in males is the result of increased hormone levels, such as testosterone. In addition to the increase in penis length and girth, the testicles descend and increase in size. Additionally, males experience an increase in body hair coverage, deepening of the voice, and a growth in height.