Growth Hormone and Male Reproductive System

A peptide hormone produced by the anterior pituitary gland, responsible for growth and development.

GH is composed of 191 amino acids and has a molecular weight of approximately 22kDa. It shares structural similarities with prolactin and placental hormones.

Specialized cells in the anterior pituitary gland that produce and release Growth Hormone.

GH is released in pulses throughout the day, with peak levels occurring during sleep, particularly deep sleep.

GH release is influenced by factors like nutrition, metabolism, age, sex steroids, adrenal hormones, thyroid hormones, and kidney and liver function.

Support cells in the testes that surround and nourish developing sperm cells, forming the blood-testis barrier.

Interstitial cells in the testes that produce and secrete testosterone, the primary male sex hormone.

The process in which semen is expelled from the penis, involving the coordinated contraction of muscles and the release of sperm and fluids from the reproductive tract.

The epididymis is where sperm cells mature and are stored. It also helps reabsorb fluids and removes old sperm cells.

The ductus deferens, or vas deferens, transports mature sperm from the epididymis to the ejaculatory duct.

The ejaculatory duct is the final pathway where sperm mixes with fluids from the seminal vesicles and prostate gland before entering the urethra.

The urethra has four parts: intramural, prostatic, membranous, and spongy. Each part has a unique function in transporting urine and semen.

The seminal vesicles produce a fluid that makes up a large portion of semen. This fluid contains nutrients like fructose and prostaglandins that support sperm.

The prostate secretes a milky fluid that adds volume and enzymes to semen, helping it liquefy after ejaculation.

The bulbourethral glands, or Cowper’s glands, produce a mucus-like fluid that neutralizes urine and lubricates the urethra before ejaculation.

Semen is a mixture of sperm and fluids from the epididymis, seminal vesicles, prostate, and bulbourethral glands.

The corpora cavernosa are two erectile tissues in the penis that fill with blood during arousal, causing erection.

Blood flow to the penis causes an erection, allowing the penis to enter the vagina and deliver sperm through the urethra.

Human Chorionic Gonadotropin (hCG), a hormone produced by the placenta, initially activates Leydig cells in the testes, leading to testosterone production. Later, Luteinizing Hormone (LH) takes over the control of Leydig cell activity.

Testosterone plays a crucial role in the development of Wolffian duct structures. These structures contribute to the development of the male reproductive system, including the epididymis, vas deferens, and seminal vesicles.

Dihydrotestosterone (DHT), a more potent form of testosterone, promotes the development of the prostate and penis during gestation and puberty.

The presence of a Y chromosome in a fertilized egg determines genetic sex. This presence is crucial for the development of male organs and characteristics.

The SRY gene, located on the Y chromosome, is responsible for the production of Testis Determining Factor (TDF). TDF initiates the development of testes, triggering a cascade of male development.

Insulin-like protein 3 (INSL3), also known as Leydig insulin-like hormone or relaxin-like factor, plays a crucial role in the transabdominal migration of testes during fetal development. It ensures their descent into the scrotum.

Puberty in males begins with an increase in pulsatile GnRH secretion. This stimulates the hypothalamic-pituitary-gonadal (HPG) axis, leading to increased testosterone production and the onset of puberty.

Increased testosterone levels during puberty lead to the development of secondary sexual characteristics such as facial and body hair growth, deeper voice, and increased muscle mass.

Increased testosterone levels during puberty stimulate the production of sperm cells in the testes, a process known as spermatogenesis. It is a continuous process that lasts throughout a man's reproductive life.

Spermatogenesis involves four distinct stages: 1) Proliferation: Spermatogonia divide by mitosis to maintain a stem cell pool. 2) Meiosis: Primary spermatocytes undergo two divisions, leading to haploid cells. 3) Spermiogenesis: Sperm cells mature in terms of shape and size changes. 4) Spermiation: Mature sperm cells are released from Sertoli cells and enter the seminiferous tubules.

Leydig cells are cells found in the testes that produce testosterone, the primary male sex hormone. They are responsible for the production of androgens, which are essential for male sexual development and function.

Follicle-stimulating hormone (FSH) is a hormone that regulates sperm production in males. It acts on Sertoli cells in the testes, stimulating their proliferation and development. It also helps regulate the production of androgen-binding protein, which is essential for testosterone transport.

Luteinizing hormone (LH) is a hormone that stimulates testosterone production in males. It acts on Leydig cells, triggering the release of testosterone, which plays a vital role in male sexual development and function.

Gonadotropin-releasing hormone (GnRH) is a hormone that stimulates the release of FSH and LH from the pituitary gland. It acts on receptors in the pituitary, triggering a cascade of events that ultimately lead to the release of gonadotropins.

The frequency of GnRH pulses affects the production of FSH and LH differently. Low-frequency pulses favor FSH production, while high-frequency pulses favor LH production.

Testosterone acts as a negative feedback signal for its own production, inhibiting the release of GnRH from the hypothalamus and the synthesis of LH from the pituitary gland, ultimately reducing testosterone production.

Inhibin B, a hormone produced by Sertoli cells, acts as a negative feedback signal for FSH. It inhibits the production and release of FSH from the pituitary gland, helping to regulate sperm production.

LH binds to receptors on Leydig cells, triggering a series of events that lead to increased testosterone production. This includes increased cholesterol mobilization, enhanced transport into the steroidogenic pathway, and increased activity of key enzymes involved in testosterone synthesis.

Steroidogenic acute regulatory protein (STAR) is a crucial protein that facilitates the transport of cholesterol into the mitochondria, the first step in testosterone synthesis.

Sex hormone-binding globulin (SHBG) is the primary binding protein for testosterone, which is produced mainly in the liver. SHBG binds to testosterone with high affinity and specificity, acting as a gatekeeper for testosterone action.

Androgen-binding protein (ABP) is a protein produced by Sertoli cells that binds to testosterone, facilitating its transport within the seminiferous tubules.

Testosterone exerts its effects through two main pathways: (1) directly through the androgen receptor, and (2) through metabolic conversion to 17𝛽-estradiol or 5𝛼-dihydrotestosterone.

Aromatase is an enzyme that converts testosterone to 17𝛽-estradiol, a form of estrogen. It is found in various tissues, including Leydig cells, adipose tissue, brain, and bone.

Testosterone, through its interaction with the androgen receptor, plays a vital role in many physiological processes, including sexual differentiation, libido, pubertal larynx growth, muscle anabolic effects, red blood cell production, and spermatogenesis stimulation.