thyroid-stimulating hormone

Examples of thyroid-stimulating 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.

• Formation, Storage, and Release of Thyroid Hormones

  • Thyroid hormones (T4 and T3) are produced by the follicular cells of the thyroid gland and regulated by thyroid-stimulating hormone (TSH).
  • The thyroid hormones thyroxine (T4) and triiodothyronine (T3) are produced from thyroid follicular cells within the thyroid gland, a process regulated by the thyroid-stimulating hormone secreted by the anterior pituitary gland.
  • T4 is believed to be a pro-hormone and a reservoir for the more active and main thyroid hormone T3.
  • If there is a deficiency of dietary iodine, the thyroid will not be able to make thyroid hormone.
  • A lack of thyroid hormone will lead to decreased negative feedback on the pituitary, which in turn, will lead to increased production of thyroid-stimulating hormone, which causes the thyroid to enlarge (goiter).

• Control of Hormone Secretion

  • A key example of a negative feedback system is the regulation of the thyroid hormone thyroxine, which regulates numerous key metabolic processes.
  • 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 these drop below the ideal value the hypothalamus is signaled to begin secreting thyroid-releasing hormone again.
  • The hormone oxytocin is produced by the posterior pituitary that stimulates and enhances contractions during labor.

• The Anterior Pituitary

  • Its regulatory functions are achieved through the secretion of various peptide hormones that act on target organs including the adrenal gland, liver, bone, thyroid gland, and gonads.
  • Thyroid-stimulating hormone is a glycoprotein hormone that affects the thyroid gland and the secretion of thyroid hormones.
  • Follicle-stimulating hormone is a glycoprotein hormone that targets the gonads and effects the growth of the reproductive system.
  • Luteinizing hormone is a glycoprotein hormone that targets the gonads to effect sex-hormone production.
  • Hormone secretion from the anterior pituitary gland is regulated by hormones 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 .

• Hormone Receptors

  • A hormone receptor is a molecule that binds to a specific hormone.
  • The hormone activity within a target cell is dependent on the effective concentration of hormone-receptor complexes that are formed.
  • Many hormones are composed of polypeptides—such as thyroid-stimulating hormones, follicle-stimulating hormones, luteinizing hormones, and insulin.
  • Lipophilic hormones—such as steroid or thyroid hormones—are able to pass through the cell and nuclear membrane; therefore receptors for these hormones do not need to be, although they sometimes are, located in the cell membrane.
  • The thyroid hormone receptor (TR) heterodimerized to the RXR.

• Development of the Endocrine System

  • This hormone, produced by the pituitary gland, is known as thyroid-stimulating hormone (TSH).
  • This is a futile attempt to synthesize thyroid hormones, for iodine levels that are too low.
  • Normally, thyroid hormones act via a negative feedback loop on the pituitary to decrease stimulation of the thyroid.
  • In goiter, the feedback loop cannot be in operation - hence continual stimulation of the thyroid and the inevitable protuberance on the neck.
  • The absence of thyroxine significantly reduces the ability of growth hormone to stimulate amino acid uptake and RNA synthesis.

• Thyroid Gland Disorders

  • Hyperthyroidism, or overactive thyroid, is the overproduction of the thyroid hormones T3 and T4 .
  • It is most commonly caused by the development of Graves' disease, an autoimmune disease in which antibodies are produced that stimulate the thyroid to secrete excessive quantities of thyroid hormones.
  • Hypothyroidism is the underproduction of the thyroid hormones T3 and T4.
  • Thyroid hormone treatment is given under the care of a physician and may take a few weeks to become effective.
  • It is termed non-toxic as it does not produce toxic quantities of thyroid hormones, despite its size.

• Action of Thyroid Hormones

  • The primary function of the thyroid is to produce the hormones triiodothyronine (T3), thyroxine (T4), and calcitonin.
  • 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.
  • The main activity of the thyroid hormones T3 and T4 is to boost the basal metabolic rates of proteins, fats, and carbohydrates as well as vitamins.
  • Thyroid hormones affect the dilation of blood vessels, which in turn affects the rate at which heat can escape the body.
  • Thyroid hormones play a particularly crucial role in brain maturation during fetal development by regulating actin polymerization during neuronal development.

• Interactions of Hormones at Target Cells

  • For example, thyroid hormones increase the number of receptors available for epinephrine at the latter's target cell, thereby increasing epinephrine's effect at that cell.
  • Without the thyroid hormones, epinephrine would have only a weak effect.
  • The two glands most responsible for homeostasis are the thyroid and the parathyroid.
  • For example, testosterone and follicle- stimulating hormones are required for normal sperm production.
  • Glucagon is a pancreatic peptide hormone that, as a counter-regulatory hormone for insulin, stimulates glucose release by the liver and maintains glucose homeostasis.