Thyroid Gland Hormones

The Location and Function of the Thyroid Gland

  • The thyroid gland is the largest gland in the human neck
  • It is located at the front of the neck (anterior) under the muscle layers
  • The thyroid gland is placed in a way that it assimilates the shape of a butterfly. This is visualised as the left and right thyroid lobes (butterfly wings) which wrap around the trachea.
  • The thyroid gland is located just under the larynx.
  • The function of the thyroid gland is to regulate the body’s metabolism by taking iodine and converting it into two thyroid hormones called thyroxine (T4) and triiodothyronine (T3).
  • Thyroid cells are exclusive in that they are the only cells in the body capable of absorbing iodine.
  • Every cell in the body depends upon thyroid gland hormones for regulation of their metabolism.
  • The thyroid gland is under the control of the pituitary gland
  • More T4 than T3 is released by the thyroid gland, but it is turned into T3 by tissues in the body, using zinc and selenium-dependent enzymes.
thyroid gland hormones and their function

The thyroid gland hormones are as follows:

Triiodothyronine (T3)

Vital roles in the regulation of the body’s metabolic rate, and oxygen usage of most cells in the body. T3 regulates heart rate, muscle strength, digestion, brain development and bone maintenance. T3 levels are decreased by inadequate dietary iodine / selenium / zinc, by auto-immune damage to the thyroid gland or by obesity / recurrent dieting / mental or physical stress / inflammation (cause T4 to be converted to reverse T3 instead of T3). Increased Reverse T3 blocks and inactivates the T3 receptor.

Thyroxine (T4)

Thyroxine’s vital role is in heart function, metabolism, digestion, brain development, bone health and muscular strength. In the bloodstream thyroxine is converted into an active form of triiodothyronine.

Regulated by the Hypothalamus and Pituitary Gland


TSH (Thyroid-stimulating hormone) plays a part in the production of thyroxine and triiodthyronine by stimulating the thyroid gland.

Thyroid Gland Disease and Hormone Deficiency

  • Thyroid disease is fivefold more common in women, and up to 20% of 60+ yo women have some degree of lowered T3 levels (hypothyroidism).
  • Symptoms of hypothyroidism include fatigue, weakness, un-refreshing sleep, low body temperature, cold sensitivity, weight gain which can’t be lost, decreased intestinal movement (indigestion, nausea, vomiting, constipation), dry/course skin/hair, menstrual irregularities, depression, brain fog, poor memory.
  • Signs include increased Low Density Lipoprotein / blood pressure / homocysteine / C-Reactive Protein.
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