Thyroid and Parathyroid hormones are part of your endocrine system. The Thyroid is a small
butterfly shaped gland at the base of the front of the neck. Most people have four pea-sized
parathyroid glands located behind their thyroid gland.
In order to make thyroid hormones, your thyroid gland needs iodine and water. Your thyroid gland
traps iodine and transforms it into thyroid hormones. If you have too little or too much iodine in
your body, it can affect the level of hormones your thyroid makes and releases and cause illness.
A full panel of Thyroid pathology includes TSH, T4, T3, RT3 and Thyroid Antibodies.
Thyroxine (T4)
Also known as Tetraiodothyronine. This is the main hormone released by the Thyroid Gland into the
bloodstream. It is a less active form of thyroid hormone and is converted into the more active T3.
Thyroxine regulates the basal metabolic rate, sensitivity to catecholamines, regulates protein
synthesis, heart, digestive function, muscle control, brain development and maintenance of bones.
Excessive amounts of T4 result in thyroid conditions such as hyperthyroidism and Grave’s Disease.
Too little production of T4 creates thyroid conditions such as hypothyroidism and Hashimoto’s
Thyroiditis. (1)
Triiodothyronine  (T3)
Triiodothyronine is the active form of the T4 hormone. Around 20% of T4 is secreted into the
bloodstream directly by the thyroid gland. The remaining 80% is produced from conversion of
thyroxine by organs such as the liver and kidneys. Similar to thyroxine, T3 affects almost every
physiological process in the body.
Reverse triiodothyronine RT3
Your thyroid makes very small amounts of RT3, which reverses the effects of T3. After its release
from the thyroid gland, T4 is converted to T3, which is active thyroid hormone, or to rT3, which is
considered an inactive form, and is incapable of the metabolic activity normally carried out by T3. In
some people with Thyroid conditions, the RT3 becomes dominant.
Researchers believe the body produces rT3 in times of severe illness or starvation.
Thyrotropin-releasing hormone (TRH), or Thyroid Stimulating Hormone (TSH)
Your hypothalamus releases TRH, which triggers your pituitary gland to release thyroid-stimulating
hormone (TSH), which stimulates your thyroid to release Thyroxine (T4) and triiodothyronine (T3).
Once your thyroid releases T4, it is transformed into T3 so that it can impact your cells and your
metabolism. In infants it is critical for brain development. A fetus will start to use its own thyroid at
around 12 weeks gestation, utilising the mothers hormones, until it produces enough of its thyroid
hormones at around 18-20 weeks. (2)
Calcitonin is made and released by your thyroid gland to help regulate calcium levels in your blood
(not bones) by decreasing it. Calcitonin opposes the actions of the parathyroid hormone, which is a
hormone that increases your blood calcium levels.
Parathyroid Hormone (PTH)
PTH is a hormone that your parathyroid glands make and release to control the level of calcium in
your blood, not your bones. PTH also helps control the levels of phosphorus and Vitamin D in your

blood and bones. PTH levels are mainly controlled by a feedback loop of calcium levels in your blood
to your parathyroid glands. Low calcium levels in your blood stimulate parathyroid hormone
release, whereas high calcium levels in your blood prevent your glands from releasing parathyroid
hormone. (3)
1. Thyroxine | You and Your Hormones from the Society for Endocrinology. (n.d.).
2. Professional, C. C. M. (n.d.-h). Thyroid hormone. Cleveland Clinic.
3. Professional, C. C. M. (n.d.-g). Parathyroid hormone. Cleveland Clinic.
Written by: Natalia Kay, Clinical Nutritionist for Pure Health Solutions