GnRH, LH, FSH, Estrogen & Testosterone

GnRH (Gonadotropin-Releasing Hormone)

  • Name(s): Gonadotropin-Releasing Hormone (GnRH)

  • Chemical Class: Peptide

  • What organ makes/secretes: Hypothalamus

  • What specific cell makes/secretes: GnRH-producing cells of the hypothalamus

  • How does the specific cell make the hormone: Synthesized in the hypothalamus and secreted into the bloodstream.

  • How does the hormone travel through the blood: Enters the bloodstream and travels via the hypothalamic-hypophyseal portal vein to the anterior pituitary.

  • Target organ: Anterior pituitary.

  • Target cell: Gonadotropic cells (gonadotropes).

  • Where it binds to its receptor: Binds to GnRH receptors on gonadotropic cells, activating signal transduction pathways.

  • What effect hormone has: Stimulates the anterior pituitary to release FSH and LH.

  • Hyposecretion: Insufficient production of FSH and LH; associated with hypogonadotropic hypogonadism.

  • Hypersecretion: Can lead to precocious puberty or hypothalamic tumors.

  • What causes release (stimulus): Low testosterone, puberty timing cues, optimal estrogen levels.

  • What prevents release (inhibition): Very low estrogen levels and high estrogen levels during pregnancy.

LH (Luteinizing Hormone)

  • Name(s): Luteinizing Hormone (LH)

  • Chemical Class: Glycoprotein

  • What organ makes/secretes: Anterior pituitary.

  • What specific cell makes/secretes: Gonadotropic cells of the anterior pituitary.

  • How does the specific cell make the hormone: Synthesized as a glycoprotein hormone in gonadotropic cells and released into the bloodstream.

  • How does the hormone travel through the blood: Circulates in the bloodstream and reaches target organs (gonads).

  • Target organ: Ovaries (in females) and testes (in males).

  • Target cell: Follicle cells in ovaries, Leydig cells in testes.

  • Where it binds to its receptor: Binds to LH receptors on target cells to trigger various physiological responses.

  • What effect hormone has: In females, triggers ovulation; in males, stimulates testosterone production.

  • Hyposecretion: Leads to anovulation in females, infertility in males.

  • Hypersecretion: May cause ovarian hyperstimulation syndrome (OHSS) or testicular tumors.

  • What causes release (stimulus): Stimulation by GnRH from the hypothalamus.

  • What prevents release (inhibition): High estrogen and progesterone levels inhibit LH release.

FSH (Follicle Stimulating Hormone)

  • Name(s): Follicle Stimulating Hormone (FSH)

  • Chemical Class: Glycoprotein

  • What organ makes/secretes: Anterior pituitary.

  • What specific cell makes/secretes: Gonadotropic cells of the anterior pituitary.

  • How does the specific cell make the hormone: Produced in response to GnRH stimulation from the hypothalamus and released into the bloodstream.

  • How does the hormone travel through the blood: Travels through the bloodstream to target organs (gonads).

  • Target organ: Ovaries (in females), testes (in males).

  • Target cell: Granulosa cells in ovaries, Sertoli cells in testes.

  • Where it binds to its receptor: Binds to FSH receptors on target cells.

  • What effect hormone has: Promotes follicle maturation in females and stimulates spermatogenesis in males.

  • Hyposecretion: Can lead to infertility or menstrual irregularities in females and reduced sperm production in males.

  • Hypersecretion: Possible ovarian or testicular tumors; can lead to ovarian hyperstimulation syndrome (OHSS).

  • What causes release (stimulus): Stimulation by GnRH from the hypothalamus.

  • What prevents release (inhibition): Feedback from inhibin produced by Sertoli and granulosa cells.

Estrogen

  • Name(s): Estrogen (various forms, e.g., estradiol)

  • Chemical Class: Steroid

  • What organ makes/secretes: Ovaries (mainly), adrenal glands (in smaller amounts).

  • What specific cell makes/secretes: Granulosa cells of ovarian follicles.

  • How does the specific cell make the hormone: Synthesized from androgens via aromatization in granulosa cells.

  • How does the hormone travel through the blood: Secreted into the bloodstream and bound to albumin and sex hormone-binding globulin (SHBG).

  • Target organ: Various organs including breasts, uterus, and bones.

  • Target cell: Hormone-responsive cells across various tissues.

  • Where it binds to its receptor: Binds to estrogen receptors in target cells influencing gene expression.

  • What effect hormone has: Promotes development of female secondary sexual characteristics, regulates menstrual cycle, and supports reproductive health.

  • Hyposecretion: Can cause amenorrhea, osteoporosis, and infertility.

  • Hypersecretion: Associated with estrogen receptor-positive cancers (e.g., breast cancer) and endometrial hyperplasia.

  • What causes release (stimulus): Increased FSH and LH levels stimulate estrogen production during the follicular phase of the menstrual cycle.

  • What prevents release (inhibition): High levels of progesterone and estrogen during the luteal phase inhibit further estrogen production.

Testosterone

  • Name(s): Testosterone

  • Chemical Class: Steroid

  • What organ makes/secretes: Testes (mainly) and adrenal glands (in smaller amounts).

  • What specific cell makes/secretes: Leydig cells of the testes.

  • How does the specific cell make the hormone: Synthesized from cholesterol and converted from androstenedione.

  • How does the hormone travel through the blood: Enters the bloodstream, primarily bound to sex hormone-binding globulin (SHBG) and albumin.

  • Target organ: Major target organs include the prostate, seminal vesicles, and skeletal muscle.

  • Target cell: Androgen-responsive tissues throughout the body.

  • Where it binds to its receptor: Enters cells and binds to androgen receptors in the cytoplasm/nucleus, influencing gene expression.

  • What effect hormone has: Responsible for development of male secondary sexual characteristics, sperm production, and maintenance of libido.

  • Hyposecretion: Can cause hypogonadism, infertility, and decreased libido.

  • Hypersecretion: Can lead to hyperandrogenism, prostate disorders, and increased risk of certain cancers.

  • What causes release (stimulus): Luteinizing Hormone (LH) stimulates testosterone production by Leydig cells.

  • What prevents release (inhibition): Inhibition via negative feedback from high testosterone levels, which decreases GnRH, LH, and FSH production.