gonadotropin-releasing hormone

Examples of gonadotropin-releasing hormone in the following topics:

• Hormonal Regulation of the Male Reproductive System

  • Gonadotropin Releasing Hormone (GnRH) is mainly made in the preoptic area of the hypothalamus from where it travels to the pituitary gland.
  • There it stimulates the synthesis and secretion of the gonadotropins, FSH and luteinizing hormone (LH).
  • Follicle Stimulating Hormone is released by the anterior pituitary gland.
  • Luteinizing Hormone is released by the anterior pituitary gland.
  • The hormone is released into the circulation when the sperm count is too high.

• Male Hormones

  • The onset of puberty is controlled by two major hormones: FSH initiates spermatogenesis and LH signals the release of testosterone.
  • At the onset of puberty, the hypothalamus begins secreting high pulses of GnRH, or gonadotropin-releasing hormone.
  • In response, the pituitary gland releases follicle stimulating hormone (FSH) and luteinizing hormone (LH) into the male system for the first time.
  • The Sertoli cells produce the hormone inhibin, which is released into the blood when the sperm count is too high.
  • In turn, the testes production of testosterone and the hormone inhibin inhibit the release of GnRH, FSH, and LH in a negative feedback loop.

• Pituitary Gland Disorders

  • The hypothalamus secretes a number of hormones, often according to a circadian rhythm, into blood vessels that supply the anterior pituitary; most of these are stimulatory (thyrotropin-releasing hormone, corticotropin-releasing hormone, gonadotropin-releasing hormone and growth hormone-releasing hormone), apart from dopamine, which suppresses prolactin production.
  • In response to the releasing hormone rate, the anterior pituitary produces its hormones (TSH, ACTH, LH, FSH, GH) that stimulate effector hormone glands in the body, although prolactin acts directly on the breast gland.
  • While their feedback system is therefore located in the hypothalamus, damage to the nerve endings would still lead to a deficiency in hormone release.
  • Measurement of ACTH and growth hormone usually requires dynamic testing, whereas the other hormones (LH/FSH, prolactin, TSH) can typically be tested with basal levels.
  • Generally, the finding of a combination of a low pituitary hormone together with a low hormone from the effector gland is indicative of hypopituitarism.

• Hormonal Regulation of the Reproductive System

  • During puberty, in both males and females, the hypothalamus produces gonadotropin-releasing hormone (GnRH), which stimulates the production and release of follicle stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary gland.
  • These hormones regulate the gonads (testes in males and ovaries in females); they are called gonadotropins.
  • At the pituitary, GnRH stimulates the synthesis and secretion of the gonadotropins, FSH and LH.
  • FSH production is inhibited by the hormone inhibin, which is released by the testes.
  • Prolactin levels are regulated by the hypothalamic hormones, prolactin-releasing hormone (PRH) and prolactin-inhibiting hormone (PIH) (which is now known to be dopamine).

• Hormonal Methods

  • Hormonal birth control contains steroid hormones that alter female fertility.
  • Combined hormonal contraceptives prevent ovulation by suppressing the release of gonadotropins.
  • Progesterone negative feedback decreases the frequency of gonadotropin-releasing hormone (GnRH) released by the hypothalamus, which decreases the release of follicle-stimulating hormone (FSH), and greatly decreases the release of luteinizing hormone (LH) by the anterior pituitary.
  • Progesterone negative feedback and the lack of estrogen positive feedback on LH release, prevent a mid-cycle LH surge.
  • Estrogen negative feedback on the anterior pituitary greatly decreases the release of FSH, which inhibits follicular development and helps prevent ovulation.

• Female Hormones

  • As with the male, the hypothalamic hormone GnRH (gonadotropin-releasing hormone) causes the release of the hormones FSH (follicle stimulating hormone) and LH (luteinizing hormone) from the anterior pituitary.
  • Follicle cells produce the hormone inhibin, which inhibits FSH production.
  • Progesterone assists in endometrial re-growth and inhibition of FSH and LH release .
  • As the follicles grow, they begin releasing estrogens and a low level of progesterone.
  • This mature egg follicle may rupture and release an egg in response to a surge of LH.

• Hormonal Regulation of the Female Reproductive Cycle

  • Follicle-stimulating hormone induces the proliferation of granulosa cells in the developing follicles and the expression of luteinizing hormone (LH) receptors on these cells.
  • This increased level of estrogen stimulates production of gonadotropin-releasing hormone (GnRH), which increases production of LH.
  • Ovulation is triggered by a spike in the amount of FSH and LH released from the pituitary gland.
  • Alternatively, the loss of the corpus luteum can be prevented by implantation of an embryo: after implantation, human embryos produce human chorionic gonadotropin (hCG).
  • Human chorionic gonadotropin is structurally similar to LH and can preserve the corpus luteum.

• Organs with Secondary Endocrine Functions

  • Several organs with specialized non-endocrine functions possess endocrine roles, such as hormone production and release.
  • These cells release the hormone atrial natriuretic peptide (ANP) in response to increased blood volume .
  • High blood volume causes the cells to be stretched, resulting in hormone release.
  • It must be present for GnRH and gonadotropin synthesis to occur.
  • The hormone atrial natriuretic peptide (ANP), released in response to increased blood volume, is produced by endocrine cells in the heart.

• Other Hormone-Producing Structures

  • Many tissues within the body release hormones including the placenta, kidneys, digestive system, and adipose tissue.
  • The placenta endocrine function in humans, aside from serving as the conduit for oxygen and nutrients for fetus, secretes hormones (secreted by syncytial layer/syncytiotrophoblast of chorionic villi) that are important during pregnancy, such as Human Chorionic Gonadotropin (hCG).
  • Erythropoietin is released in response to hypoxia (low levels of oxygen at tissue level) in the renal circulation.
  • It is released by muscle cells in the upper chambers (atria) of the heart (atrial myocytes) in response to high blood pressure.
  • Cholecystokinin (CCK) - is in the duodenum and stimulates the release of digestive enzymes in the pancreas and stimulates the emptying of bile in the gall bladder.

• Humoral, Hormonal, and Neural Stimuli

  • The release of hormones can be triggered by changes in the blood ("humor"), by the actions of other hormones, or by neurological stimuli.
  • Hormonal stimuli refers to the release of a hormone in response to another hormone.
  • A number of endocrine glands release hormones when stimulated by hormones released by other endocrine glands.
  • The anterior pituitary, in turn, releases hormones that regulate hormone production by other endocrine glands.
  • This in turn causes the release of the hormones T3 and T4.