Thyroid hormones are chemical messengers produced by the thyroid gland, a butterfly-shaped organ located in the neck. The main thyroid hormones are:
1. Thyroxine (T4)
Contains four iodine atoms.
It is the primary hormone produced by the thyroid gland.
It is converted into the more active hormone T3 in the liver and other tissues.
2. Triiodothyronine (T3)
Contains three iodine atoms.
It is the active form of thyroid hormone that directly affects cells and metabolism.
3. Calcitonin
A hormone involved in calcium homeostasis, produced by the parafollicular (C-cells) of the thyroid gland.
It lowers blood calcium levels by inhibiting osteoclast activity in bones.
Importance of Thyroid Hormones
Regulation of Metabolism
T3 and T4 control the rate at which the body uses energy (basal metabolic rate).
They influence how fast calories are burned and how quickly nutrients are used.
Growth and Development
Essential for normal growth in children, including brain development and skeletal growth.
A deficiency in childhood can lead to cretinism (severe developmental delay).
Temperature Regulation
Help maintain body temperature by increasing the body’s heat production.
Cardiovascular Function
Increase heart rate and cardiac output.
Help maintain proper blood pressure.
Neurological Function
Important for proper brain development and mental alertness.
Imbalances can cause symptoms such as anxiety, depression, or mental fog.
Reproductive Health
Influence menstrual cycles and fertility.
Both hypothyroidism and hyperthyroidism can lead to irregular periods or infertility.
Digestive Function
Affect the speed of digestion; too much hormone may lead to diarrhea, too little to constipation.
Common Disorders
Hypothyroidism (low hormone levels): fatigue, weight gain, cold intolerance, depression.
Hyperthyroidism (high hormone levels): weight loss, rapid heartbeat, irritability, heat intolerance.
Goiter: enlargement of the thyroid, often due to iodine deficiency.
Thyroid Nodules/Cancer: abnormal growths in the gland.