13.11: Hormonal Regulation of the Male Reproductive System
- Page ID
- 121769
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Male reproductive function is controlled by hormonal signaling between the hypothalamus, pituitary gland, and testes.
- Explain how the hypothalamus, anterior pituitary, and testes interact to regulate testosterone production and spermatogenesis.
- Differentiate the roles of LH and FSH in the male reproductive system.
Gonadotropin-Releasing Hormone (GnRH), Follicle Stimulating Hormone (FSH), and Luteinizing Hormone (LH)
Hormonal regulation of the male reproductive system is controlled largely by the hypothalamus and the anterior pituitary. The hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to synthesize and secrete the gonadotropins: luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
These hormones travel through the bloodstream to the testes, where they regulate testosterone production and support spermatogenesis.
Are you wondering why the male hormones are called LH and FSH, so clearly related to female reproductive functions?
The names reflect their initial discovery in female physiology, not their roles in males. hey were named for the first effects scientists observed in females long before their roles in males were understood. Unfortunately, the original names stuck even after researchers discovered they regulate testes function as well.
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LH was named because it triggers formation of the corpus luteum in the ovary. In the male LH targets the Leydig cells located in the interstitial spaces between seminiferous tubules — (which is why the Leydig cells are also called interstitial cells, remember?). LH promotes these Interstitial cells to produce testosterone.
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FSH was named so because it stimulates ovarian follicles. In the male, FSH acts on the Sertoli cells (sustentacular cells) inside the seminiferous tubules. In response to FSH, Sertoli cells produce androgen-binding protein (ABP), which concentrates testosterone within the tubules. This high local testosterone level is essential for stimulating the spermatogenic cells and supporting the full process of spermatogenesis.
Figure \(\PageIndex{1}\): How the Brain Orchestrates Male Reproductive Function. The hypothalamus releases GnRH to stimulate the anterior pituitary, which secretes FSH and LH. FSH acts on Sertoli cells to support spermatogenesis and triggers the release of inhibin, which provides negative feedback to the pituitary. LH stimulates Leydig cells to produce testosterone, which promotes spermatogenesis and provides negative feedback to both the hypothalamus and anterior pituitary.
Testosterone
Testosterone is an androgen and a steroid hormone produced by the Leydig (interstitial) cells that lie between the seminiferous tubules of the testes. In male embryos, Leydig cells begin secreting testosterone by the seventh week of development, with levels peaking in the second trimester. This early surge drives the anatomical differentiation of male reproductive structures. After birth, testosterone levels remain low throughout childhood, then rise sharply during puberty to trigger characteristic physical changes and initiate spermatogenesis.
Functions of Testosterone
Within the testes, very high local concentrations of testosterone support Sertoli cells, maintain the structure and function of the seminiferous tubules, and are essential for ongoing spermatogenesis. Even if blood testosterone levels are normal, a drop in intratesticular testosterone can significantly reduce or halt sperm production.
Once testosterone enters the bloodstream, it acts as a classic hormone influencing a wide range of target tissues. In skeletal muscle, testosterone increases protein synthesis, which supports muscle enlargement, strength, and overall growth. It also travels to the brain, where it enhances sexual desire and stimulates the production and release of Growth Hormone (GH). GH works together with testosterone to promote bone growth, especially during the adolescent growth spurt. In fact, the dramatic rise in testosterone during puberty helps explain why males typically reach greater adult height than females. Beyond contributing to a taller and stronger physique, testosterone is essential for the development and long-term maintenance of male secondary sexual characteristics, including facial and body hair, a deeper voice, and increased muscle mass.
Before birth, testosterone plays a key role in forming the male reproductive system. It supports the development of the Wolffian ducts, which mature into structures such as the epididymis, ductus deferens, and seminal vesicles. By guiding both internal and external reproductive anatomy, testosterone helps establish the basic male reproductive pathways well before birth.
In females, small amounts of testosterone are produced by the ovaries (with most converted to estradiol), and the adrenal glands of both sexes contribute additional minor amounts.
Regulation of Testosterone Production
The body carefully controls testosterone concentrations because normal levels are essential for male reproductive function. This regulation depends on communication between the hypothalamus, the anterior pituitary gland, and the testes.
As you have seen above, the process begins in the hypothalamus, which releases gonadotropin-releasing hormone (GnRH) in small pulses. GnRH travels to the anterior pituitary and stimulates the release of two key hormones: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Although they were first discovered in females, LH and FSH are equally important in males.
In the testes, LH binds to receptors on Leydig cells, stimulating them to produce testosterone. FSH acts mainly on Sertoli cells inside the seminiferous tubules, supporting spermatogenesis. Sertoli cells also release inhibin, a hormone that helps regulate FSH secretion.
Testosterone production is controlled by a negative feedback loop. When blood testosterone levels are low, the hypothalamus increases its release of GnRH, which in turn increases LH secretion and stimulates Leydig cells to produce more testosterone. When testosterone levels rise, the hormone binds to receptors in both the hypothalamus and the anterior pituitary, reducing the release of GnRH and LH. This decrease slows testosterone production until levels fall again and the cycle repeats.
Clinical Correlation
Some athletes use anabolic steroids to increase muscle mass and strength. These drugs are synthetic forms of male sex hormones that act like very strong testosterone. When a person takes anabolic steroids, the negative feedback loop causes the hypothalamus to reduce its release of GnRH, and the pituitary gland lowers its secretion of LH and FSH. With less LH and FSH reaching the testes, the Leydig cells produce less natural testosterone inside the testes and the Sertoli cells receive less stimulation to support sperm production. As a result, spermatogenesis can slow down or even stop, sperm counts may drop, and the testes can shrink in size. Over time, this hormonal imbalance can lead to reduced fertility or temporary infertility, and in some cases the effects may last even after steroid use has stopped.
