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The Thyroid Gland

The Thyroid Gland

Located in the base of the neck the thyroid gland is recognised by its butterfly like shape, with a lobe either side of the trachea. The gland regulates many vital body functions including:

  • Heart rate,
  • Central nervous system
  • Peripheral nervous system,
  • Respiration,
  • Body weight,
  • Muscle strength,
  • Body temperature,
  • Cholesterol levels,
  • Menstrual cycles.
As part of the endocrine system the thyroid gland produces, stores and releases hormones into the bloodstream. Using Iodine from the diet the thyroid gland produces 2 main hormones Triiodothyronine (T3) and Thyroxine (T4). The balance between these two hormones is regulated by the hypothalamus and pituitary gland to help ensure levels do not become too high or too low. Overall the level of these 2 hormones affect the bodies metabolic rate. However T4 can be considered relatively inactive, with 80% of T3 produced from the conversion of T4 in the liver or kidneys. The remaining 20% of T3 is produced in the thyroid gland. The thyroid gland is also recognised to produce calcitonin, a hormone involved in the regulation of calcium levels.


How the thyroid gland works

Thyrotrophin-releasing hormone (TRH) released from the hypothalamus and Thyroid-stimulating hormone (TSH) released by the pituitary gland are part of a feedback loop to regulate the levels of T4 and T3 in circulation. TRH signals to the pituitary to release TSH, this hormone may then stimulate the thyroid gland to release T4 and T3.

When T4 and T3 are detected at low levels in the blood the pituitary releases more TSH to compensate.

When T4 and T3 are detected at higher levels in the blood the pituitary gland is signalled to release less TSH.


Due to the fine balance between these hormones and their varied effect on cells within the body if levels are disrupted different physiological effects may be seen.

Hyperthyroidism is a condition caused by an overactive thyroid, this means the gland produces excessive amounts of thyroid hormone (t4 and T3). This in turn speeds up the body's metabolic processes and can cause symptoms such as: 

  • Anxiety, nervousness
  • Irritability, mood swings
  • Heat intolerance, sweating
  • Heart palpitations
  • Hand tremors
  • Hair loss
  • Missed or light menstrual cycles
  • Skin dryness
  • Trouble sleeping
  • Weight loss
  • Increased appetite
  • Increased bowel movements
The cause for this may be an autoimmune disorder Graves disease. This is a disease more often found in women that tends to runs in families. Whereby the body produces an antibody called TSI (thyroid stimulating immunoglobulin) which stimulates the gland to produce the hormones in excess. Alternatively it may be influenced by lumps or nodules on the gland seen as a goiter. Inflammation of the gland known as thyroiditis. Or over consumption of iodine from medication, food or supplements.

Diagnosis for hyperthyroidism can be carried out from measuring levels of T4 and T3 within the blood or ultrasound scans.

Following diagnosis treatment can include antithyroid medication that interfere with the production of thyroid hormones. Radioactive iodine therapy, that helps to damage cells within the thyroid. Or in rare cases surgery to remove the excess tissue or the organ completely. The treatment selected will depend upon the severity of the case and the underlying cause. Beta blockers can also be used alongside this, to help block the effects on tissues throughout the body. For instance helping to slow down heart rate and prevent hand tremors. 


Hypothyroidism is a condition caused by insufficient levels of thyroid hormone, reducing the body's metabolic processes. This is very common medical condition particularly within women causing symptoms such as:

  • Fatigue
  • Weakness
  • Depression
  • Weight gain
  • Cold intolerance
  • Muscle cramps, aches
  • Coarse, dry hair
  • Rough pale skin
  • Puffiness around the eyes
  • Constipation

This may be caused by inflammation of the thyroid gland leading to damage or death of the cells. An autoimmune disease called Hashimoto's thyroiditis is recognised to induce inflammation caused by the patients own immune system. The treatment of hyperthyroidism such as surgery of radioactive iodine treatment may also leads to hypothyroidism if too much of the gland is removed or too many cells destroyed. Alternatively the thyroid gland may be functioning correctly but the problem stems from the pituitary gland. If the pituitary gland is not producing enough TSH then the thyroid gland is not receiving enough signal to stimulate the release of T4 and T3. Treatment for hypothyroidism often involves medication to increase thyroid hormone levels. Treatment is essential as if low levels of thyroid hormone are detected in circulation this signals to the pituitary to release more TSH. If the thyroid gland is exposed to constant high levels of TSH this can lead to over stimulation, causing the gland to become enlarged and the formation of a goitre.