thyroid

Examples of thyroid in the following topics:

• 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.
  • 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).
  • This enlarged endemic colloid goiter has the effect of increasing the thyroid's ability to trap more iodide, compensating for the iodine deficiency and allowing it to produce adequate amounts of thyroid hormone.

• 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.
  • Thyroid hormones also provide negative feedback to the hypothalamus and anterior pituitary gland.
  • When thyroid levels in the blood are elevated TSH and TRH production is reduced.
  • 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.
  • Thyroid hormones provide negative feedback, inhibiting secretion of TRH and TSH when blood levels are high.

• Thyroid Gland Disorders

  • Thyroid disorders include hyperthyroidism (abnormally increased activity), hypothyroidism (abnormally decreased activity), and thyroid nodules, which are generally benign thyroid neoplasms, but may be thyroid cancers.
  • Hyperthyroidism, or overactive thyroid, is the overproduction of the thyroid hormones T3 and T4 .
  • Hypothyroid disorders may occur as a result of congenital thyroid abnormalities, autoimmune disorders such as Hashimoto's thyroiditis, iodine deficiency (more likely in poorer countries), or the removal of the thyroid following surgery to treat severe hyperthyroidism or thyroid cancer.
  • Negative feedback mechanisms result in growth of the thyroid gland when thyroid hormones are being produced in sufficiently low quantities as a means of increasing the thyroid output.
  • Differentiate among the types of thyroid gland disorders: hyperthyroidism, hypothyroidism, and thyroid nodules

• Action of Thyroid Hormones

  • The primary function of the thyroid is to produce the hormones triiodothyronine (T3), thyroxine (T4), and calcitonin.
  • Triiodothyronine (T3) and thyroxine (T4) are enzymes produced by the thyroid gland.
  • 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.
  • A person who suffers from hyperthyroidism (an over-active thyroid) will experience a fever; conversely, a person who suffers from hypothyroidism (a less active thyroid) will experience a decrease in body temperature.

• Thyroid Gland

  • When the thyroid swells due to dysfunction, it can be felt under the skin of the neck.
  • The thyroid gland is made up of many spherical thyroid follicles which are lined with a simple cuboidal epithelium.
  • This glycoprotein is the precursor to the thyroid hormones.
  • The thyroid gland produces the hormones T3 (triiodothyronine) and T4 (thyroxine).
  • These thyroid hormones increase the rates of mitochondrial ATP production.

• Overview of the Thyroid Gland

  • In vertebrates, the thyroid gland is one of the largest endocrine glands.
  • It is found in the neck, below the thyroid cartilage that forms the laryngeal prominence, or Adam's apple.
  • The thyroid also produces calcitonin, which plays a role in calcium homeostasis.
  • 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 .
  • Thyroid function is regulated by the actions of the hypothalamus and pituitary gland.

• Development of the Endocrine System

  • The thyroid gland is the primary endocrine gland involved in development.
  • The thyroid gland is one of the largest endocrine glands in the body.
  • Normally, thyroid hormones act via a negative feedback loop on the pituitary to decrease stimulation of the thyroid.
  • Unfortunately thyroid conditions require lifelong treatment and because of the body's need for a sensitive balance of thyroid hormone both supplementing and suppressing thyroid function can take months or even years to regulate.
  • Thyroid gland 4.

• 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 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.

• Hormonal Regulation of Metabolism

  • The levels of glucose in the blood are regulated by the hormones insulin and glucagon from the pancreas, and T3 and T4 from the thyroid.
  • Additional regulation is mediated by the thyroid hormones.
  • T3 and T4 release from the thyroid gland are stimulated by thyroid-stimulating hormone (TSH), which is produced by the anterior pituitary.
  • Disorders can arise from both the underproduction and overproduction of thyroid hormones.
  • Hypothyroidism, underproduction of the thyroid hormones, can cause a low metabolic rate leading to weight gain, sensitivity to cold, and reduced mental activity, among other symptoms.

• Type II (Cytotoxic) Reactions

  • Graves' disease is an autoimmune disease where the thyroid is overactive, producing an excessive amount of thyroid hormones (a serious metabolic imbalance known as hyperthyroidism and thyrotoxicosis).
  • This is caused by thyroid autoantibodies that activate the Thyroid Stimulating Hormone receptor, thereby stimulating thyroid hormone synthesis and secretion, and thyroid growth (causing a diffusely enlarged goiter).