Thyroid Hormones

Thyroid hormones are a butterfly gland in the front of the neck and below the larynx and has two lobes that lie on the sides of the leg just below the larynx. The gland weighs about 15 to 25 grams. The two parts of the thyroid gland are connected by a thin film that is called the Isthmus thyroid. The thyroid gland uses food iodine to make thyroid hormones called thyroxine (T4) and triiodothyronine (T3). The thyroid gland stores these hormones and releases them when needed.

Thyroid hormones are essential for normal brain development, especially in the first three years of life. Children of older ages also need thyroid hormones to grow and evolve naturally, and adults depend on these hormones to regulate metabolism and use energy.

Thyroid hormones are tests that test thyroid gland function. The thyroid gland produces hormones that regulate how the body uses energy.

Thyroid hormones

Thyroid hormones

Thyroid stimulating hormone (TSH)

The thyroid stimulating hormone (TSH) is a hormone released from the anterior part of the pituitary gland. This hormone increases the thyroid hormones secretion and increases the level of thyroid hormones by lowering the blood levels of thyroid hormones. Measuring the blood level of this hormone is very useful in treating hypothyroidism or hyperthyroidism, and it is a selective test for neonatal hypothyroidism screening.

The thyroid hormone plays a central role in controlling thyroid function and is the most useful physiological indicator of thyroid hormone activity. The main factor is determining the adjustment point in the thyroid hormones axis of the TSH. The secretion of this hormone is regulated by the hypothalamic TRH hormone. TRH is the major stimulant for the synthesis and secretion of TSH. Approximately 15 minutes after administration of TRH, the amount of TSH secretion reaches its maximum.

  • TSH, like other pituitary hormones, is secreted in rash and its secretion varies overnight at different times.
  • The level of TSH is fluctuating around the clock, with a minimum level of secretion at 10 o’clock in the morning and a maximum level of secretion of the hormone at 10 o’clock.

Increased TSH

Primary hypothyroidism
Thyroid agenesis
Congenital Curtinism
High doses of iodine
Radioactive iodine injection
Thyroid withdrawal with surgery
Severe and chronic illnesses

Reduced TSH

Secondary hypothyroidism
Suppressive doses of thyroid drugs
Artificial hyperthyroidism (thyroid medication arbitrarily inhibits TSH production)
Toxic goiter
Graves disease

Thyroid hormones

Thyroid hormones (T3 and T4) are derived from tyrosine amino acids. About 95% of the hormone secreted from the thyroid gland is called T4 (thyroxine). Although the level of T3 secretion from the thyroid gland is negligible, this hormone plays a major role. The main part of the blood T3 is from the conversion of T4 to T3 in peripheral tissues such as the liver, kidneys, and pairs.

Thyroid deficiencies

The complications of thyroid disorders appear as hyperexcitations. Hypothyroidism shows slowly. Depression may occur for various reasons:

  • Thyroid gland failure in thyroid hormones; due to iodine deficiency or lack of enzymes needed to produce hormones
  • Disruption of TSH secretion from the pituitary gland
  • Disruption of TRH secretion from the hypothalamus
  • A type of autoimmune disease that results in the destruction of thyroid gland cells and is known as Hashimoto.

Other factors include:


  • TSH-producing cancer cells in the pituitary gland
  • TRH-secreting cancer cells in the hypothalamus
  • Administration of excess iodine

T4 (Thyroxine)

About 99% of thyroxin is in the blood protein bound (TBG and albumin), and only 1-5% T4 is free. Free T4 is a form of active thyroid hormone metabolism. This test is used to diagnose thyroid function and monitor alternative and repressive therapies. In this test, the total thyroxine value (binding and non-binding) is measured.

  • This test is used to screen infants for the diagnosis of hypothyroidism.
  • Any increase in the amount of thyroxine-binding proteins (such as birth control pills and pregnancy) causes a false increase in T4 levels.
  • Increased over-normal T4 is a sign of hyperthyroidism (hyperthyroidism) and lower than normal levels indicating hypothyroidism (hypothyroidism).

Increased T4

T4 levels in primary hyperthyroidism (Graves’ disease, plumor disease, toxic thyroid adenoma), acute thyroiditis, hereditary dislocation of hyperthyroidism, synthetic hyperthyroidism (T4 arbitrary), stroma ovaries (thyroid tissue in the ovary or anywhere else in the body) and increased TBG In pregnancy, hepatitis and congenital hyperproteinemia increase.

Reduced T4

T4 levels in hypothyroidism (curitism, surgical gland removal, micas), pituitary and hypothalamic deficiency (lack of adequate TRH), protein malnutrition (decreased protein production (TBG), protein deficiency (eg, nephrotic syndrome), iodine deficiency, non- Thyroidism (such as renal failure, Cushing’s disease, cirrhosis, advanced surgery and cancer) and decreased TBG levels.

Increase FT4

FT4 in primary hyperthyroidism (grave, plaque, toxic venous adenoma), acute thyroiditis, synthetic hyperthyroidism and stroma virus
(Excessive thyroid tissue in the ovary or anywhere in the body).

Reduced FT4

The rate of FT4 in Hypothyroidism (crytinism, thyroid ablation, micas), hypophysis and hypothalamic deficiency, iodine deficiency and non-thyroid disease (renal failure, Cushing’s disease, cirrhosis, surgery, advanced cancer).

T3 Uptake or T3RU

Indirect measurement of proteins carrying thyroid hormones in the blood. Evaluation of carrier proteins can be helpful in T3 and T4 test results. The T3 Uptake test is directly related to serum unsaturated TBG, which means that the percentage of free T4G T4s that are considered to be a criterion for T4 is serum free. The T3 Uptake measurement alone is not useful but is used in conjunction with the measurement of T4 in the FT4I calculation.

FT4I =(T4 concentration) x (% T3-uptake) /100

  • T3 Uptake values plus T4 are used to estimate free thyroxine index (FT4I).
  • Renal damage, hyperthyroidism, nephrotic syndrome and malnutrition increase T3 uptake
  • Acute hepatitis, pregnancy, hypothyroidism and estrogen use reduce T3 uptake.
  • In recent years, using T3RU has been reduced by measuring FT4 and TBG levels.
  • Hyperthyroidism increases the FTI and T3RU and causes hypothyroidism.

Parathyroid hormone

Parathyroid glands are located in the posterior part of the thyroid lobe. Typically, two tubers are placed on top and two tubers are placed at the bottom. In the tissue structure of the parathyroid glands, cells known as ‘core cells’ are known to release the parathyroid hormone (PTH) secretion.

The fastest changes are related to the effect of hormone on the kidney, but most of the effects are on hormone effects on the bone. In cases of long-term deficiency of calcium, dietary intake and inadequate intake of calcium from the intestinal PTH with bone metabolism prevent the blood from calcium loss.

Parathormone also plays a role in the metabolism of phosphorus (phosphate) when the PTH promotes the dissolution of the bone mineral matrix and calcium phosphate is released from the bone, PTH increases the phosphorylation of the renal coli. As a result, the effect of PTH on the bone and The kidneys increase the concentration of calcium in the extracellular fluid and decrease the concentration of extracellular fluid phosphate.

Parathorm elevators


  • Parathyroid hyperhidrosis (hyperparathyroidism) is called overproduction of PTH, which increases the amount of calcium in the blood.
  • PTH synthesis may be increased due to an increase in the size and number of major PTH-producing cells in the parathyroid gland, due to the long-term lack of calcium in the blood or vitamin D.
  • Deficiency of calcium and vitamin D
  • Chronic renal failure
  • Malnutrition syndrome

Parathorm level reducing agents


  • Parathyroid hernia (hypoparathyroidism) is caused by PTH deficiency, which reduces serum calcium ionization and increases phosphate levels. Parathyroidism is rare and occurs in children more than adults.
  • Tissue removal by surgery or by immunological method
  • Increasing calcium reduces parathyroid hernia.
  • In poisoning with vitamin D, intestinal calcium intake is increased and calcium levels increase, resulting in decreased parathyroid gland.



  • To perform this test, the patient should be fasting for 12 hours, but no drinking water.
  • The highest amount of pteratorum is at 2 am and its lowest value at 2 pm. Typically, sampling for this experiment takes place at 8am.
  • The specimen should be isolated in the shortest possible time and stored in the freezer.
  • The simultaneous measurement of parathormone and calcium and phosphorus in differential diagnosis is important.

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