What The Thyroid Does As A Part Of Endocrine System

Thyroid In Endocrine System

The endocrine system is composed of many different glands, which the main function is to manufacture specific hormones. Hormones are chemical substances that transport a signal from one cell to another and are necessary for cellular communication and regulation.

Endocrine glands

  • Pituitary gland is located at the base of the brain and produces hormones that control the activities of numerous other glands.
  • Thyroid gland produces thyroid hormones that control metabolism, the body’s temperature, growth and development.
  • Parathyroid glands are connected to the thyroid and control the levels of calcium in the blood.
  • Pineal gland is located in the brain and responsible for release of melatonin.
  • Adrenal glands sit on top of the kidneys near the spine and produce over fifty hormones that help to cope with stress and regulate mineral, fluid and glucose balance.
  • Pancreas regulates blood sugar levels through insulin production and releases digestive enzymes.
  • Gonads, ovaries and testicles, regulate fertility and secondary sexual characteristics.

Endocrine Glands

What are hormones?

Most hormones are proteins made of tens to hundreds of amino acids. For example, modified molecules of amino acid tyrosine and several iodine atoms build thyroid hormones thyroxine (T4) and triiodothyronine (T3).

Other hormones are modified amino or fatty acids or derivatives of cholesterol, which is a precursor of most steroid hormones. The endocrine glands are interrelated and most hormones have another hormone that regulates its secretion.

Many hormones function as a part of a cascade, so that the target tissue is another endocrine gland. Classic examples of a cascade hormone production would be a Hypothalamic – Pituitary – Adrenal Axis and Hypothalamic – Pituitary – Thyroid Axis.


Hypothalamic – Pituitary – Thyroid Axis

In the case of the thyroid gland, hypothalamus located above the pituitary gland at the base of the brain, releases Thyrotrophine Releasing Hormone (TRH). TRH signals to the pituitary gland how much Thyrotrophine or thyroid stimulating hormone (TSH) to produce. The pituitary gland produces TSH to control the thyroid gland and keep thyroid hormones at the normal levels.  This cascade of hormonal reactions calls Hypothalamic – Pituitary – Thyroid Axis. 

The thyroid gland has receptor sites, which receive TSH. TSH links up with these receptors and then the cells are stimulated to produce and release two main thyroid hormones T4 and T3. These hormones have an effect on the function of target cells in other parts of the body.

The amount of TSH produced depends on body’s needs in thyroid hormones: the more thyroid hormones required, the more TSH produced by pituitary. Hypothalamus constantly monitors the levels of thyroid hormones in the bloodstream to maintain the correct balance.

When T4 and T3 levels in the blood are low, TRH and TSH increase and signal to the thyroid gland to produce more thyroid hormones. Once the thyroid hormones reach a normal level, feedback inhibition on the hypothalamus and pituitary gland keeps hormone levels from becoming too high.

Hormonal imbalances

Endocrine glands secrete hormones that perform specific functions by acting on target cells and interacting with other hormones via complex feedback system. When something disrupts the pathways then the endocrine system starts to malfunction and hormonal abnormalities occur. All endocrine disorders result from disruption of the normal feedback mechanisms.

Autoimmune diseases often cause hormone deficiency when specific antibodies destroy an endocrine gland. A healthy body normally produces antibodies to defend against invaders such as viruses and bacteria. In Hashimoto’s thyroiditis the antibodies attack the healthy cells and tissues of the thyroid gland and cause inflammation. Inflammatory process may result in thyroid gland destruction and thyroid hormone deficiency called hypothyroidism.

All hormones produced in the body are interconnected and affect the function of each other. Estrogen, progesterone and testosterone work together to keep the body functioning well and naturally start to decline when people reach their 40s and sometimes earlier. The levels of insulin and cortisol have a tendency to increase with the age and contribute to the aging process. Restoring hormones can have a profound impact on the physical and emotional well-being.

A malfunction of one of these hormones interferes with the function of the others. The combination of natural hormonal shifts and lifestyle factors may trigger multiple hormonal imbalances:

  • When thyroid hormone declines, the production of all the other hormones especially estrogen, progesterone, and androgens will be impacted, increasing the risk of fibroids and fibrocystic breast disease.
  • When cortisol levels are low, caused by adrenal insufficiency, the thyroid gland is less efficient at doing its job of increasing energy and metabolic activity.
  • When cortisol is high due to stress, it creates a thyroid hormone resistance. In this condition, thyroid hormone levels can be normal, but tissues fail to respond as efficiently to the thyroid signal and require more hormones to create the same effect. Hormone resistance due to high cortisol applies to all other hormones such as insulin, progesterone, estrogen and testosterone.
  • The combination of high cortisol levels and low thyroid levels cause weight gain despite of healthy diet and regular exercise.
  • Excess estrogen inhibits thyroid action and lowers the rate of metabolism. In the opposite case, progesterone supports thyroid function.
  • Low levels of estrogen, progesterone, or testosterone lead to erratic production of thyroid, insulin, and cortisol.

When the major hormones fall out of balance, with the time it may result in a serious health issues and an onset of degenerative diseases. Knowing what the major hormones do in the body and what happens when hormone deficiency occurs, helps to prevent diseases development and contributes to your overall health and well being.

There is a lot more to discover about hypothyroidism and Hashimoto’s thyroiditis, so sign up for Outsmart Disease Newsletters and get FREE e-mail course Nutritional guide for Hashimoto’s disease to learn more.

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About Marina Gutner, PhD

Marina Gutner, PhD, researcher, medical writer, thyroid blogger, founder and Admin of Outsmart Disease who writes about life-changing treatments for hypothyroidism, Hashimoto's thyroiditis and autoimmune disease and how to balance hormones in women