thyrotropin-releasing hormone

(noun)

A hormone released from the hypothalamus that stimulates thyroid-stimulating hormone production from the anterior pituitary gland.

Related Terms

Examples of thyrotropin-releasing hormone in the following topics:

  • Control of Thyroid Hormone Release

    • The production of thyroxine and triiodothyronine is regulated by thyroid-stimulating hormone (TSH) that is released from the anterior pituitary.
    • The production of thyroxine (T4) and triiodothyronine (T3) is primarily regulated by thyroid-stimulating hormone (TSH) that is released from the anterior pituitary gland.
    • TSH release, in turn, stimulates the hypothalamus to secrete thyrotropin-releasing hormone (TRH).
    • Thyroid hormones also provide negative feedback to the hypothalamus and anterior pituitary gland.
    • Thyroid hormones are produced from the thyroid under the influence of thyroid-stimulating hormone (TSH) from the anterior pituitary gland, which is itself under the control of thyroptropin-releasing hormone (TRH) secreted by the hypothalamus.

  • Overview of the Thyroid Gland

    • The thyroid gland, in the anterior neck, controls body metabolism, protein synthesis, and a body's responsiveness to other hormones.
    • The thyroid gland controls how quickly the body uses energy, makes proteins, and controls how sensitive the body is to other hormones.
    • It participates in these processes by producing thyroid hormones, the principal ones being triiodothyronine (T3) and thyroxine (sometimes referred to as tetraiodothyronine (T4)).
    • These hormones regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body.
    • The hormonal output from the thyroid is regulated by thyroid-stimulating hormone (TSH) produced by the anterior pituitary, which itself is regulated by thyrotropin-releasing hormone (TRH) produced by the hypothalamus .

  • 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.

  • Hypothalamus

    • The hypothalamus contains thyrotropin-releasing hormone, gonadotropin-releasing hormone, growth hormone-releasing hormone, corticotropin-releasing hormone, somatostatin, and dopamine, as well as vasopressin and oxytocin.
    • These hormones are released into the bloodstream and target other organ systems, most notably the pituitary.
    • Most of the hypothalamic hormones generated are distributed to the pituitary via the hypophyseal portal system.
    • The hypothalamus coordinates hormonal and behavioral circadian rhythms, complex patterns of neuroendocrine outputs, complex homeostatic mechanisms, and important behaviors.
    • This is important for the uptake of circulating hormones and to determine concentration of substances in the blood.

  • Chemistry of Hormones

    • There are three classes of hormones: peptide hormones, lipid hormones, and monoamine hormones.
    • A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism.
    • Some peptide hormones contain carbohydrate side chains  and are termed glyco-proteins, such as the follicle-stimulating hormone.
    • All peptide hormones are hydrophilic and are therefore unable to cross the plasma membrane alone.
    • Eicosanoids are also lipid hormones that are derived from fatty acids in the plasma membrane.

  • Hormonal Regulation of the Male Reproductive System

    • Hormonal control of spermatogenesis varies among species.
    • Gonadotropin Releasing Hormone (GnRH) is mainly made in the preoptic area of the hypothalamus from where it travels to the pituitary gland.
    • 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.

  • Control of Hormone Secretion

    • A hormone is a molecule released by a cell or a gland in one part of the body that exerts effects via specific receptors at other sites.
    • Briefly, neurons in the hypothalamus secrete thyroid-releasing hormone that stimulate cells in the anterior pituitary to secrete thyroid-stimulating hormone.
    • The thyroid-stimulating hormone then stimulates the release of thyroxine from the thyroid gland.
    • When the blood concentration of thyroxine rises above the ideal value as detected by sensory neurons, the hypothalamus is signaled to stop thyroid-releasing hormone production, which eventually lowers the levels of thyroxine in the blood.
    • When these drop below the ideal value the hypothalamus is signaled to begin secreting thyroid-releasing hormone again.

  • Hormones of the Digestive System

    • This hormone responds to the acidity of the chyme.
    • Ghrelin is a hormone that is released by the stomach and targets the pituitary, signaling to the body that it needs to eat.
    • PYY is a hormone that is released by the small intestine and counters ghrelin.
    • It is released by the hypothalamus and signals that you have just eaten and helps to suppress our appetite.
    • The pancreas releases the hormone insulin, which targets the hypothalamus and also aids in suppressing our appetite after we have just eaten and there is a rise in blood glucose levels.

  • Transport of Hormones

    • Hormones synthesized by the endocrine glands are transported throughout the body by the bloodstream.
    • For example, hormones secreted by the pancreas pass into the hepatic portal vein that transports them directly to the liver.
    • Mainly produced in the liver, these transport proteins are hormone specific, such as the sex hormone binding globulin that binds with the sex hormones.
    • When bound with a transport protein hormones are typically inactive, and their release is often triggered in regions of low hormone concentration or can be controlled by other factors.
    • Describe the way in which hormones are transported in the endocrine system

  • Action of Thyroid Hormones

    • The primary function of the thyroid is to produce the hormones triiodothyronine (T3), thyroxine (T4), and calcitonin.
    • T4 is thought to be a pro-hormone to the more metabolically active T3.
    • Calcitonin is another hormone released by the thyroid gland that is responsible for modulating blood calcium levels in conjunction with parathyroid hormone, which is released from the parathyroid.
    • Only a very small fraction of the circulating hormone is free—T4 0.03% and T3 0.3%.
    • Only the free fraction has hormonal activity.