Thyroid Function

The thyroid gland is a small butterfly shaped gland located in the neck just below the Adam’s apple and above the collar bone. It sits in front of the trachea. The word thyroid is Greek for “shield shaped”.

The thyroid gland weighs approximately 20 grams. Each lobe is approximately 4 cm (1.6 inches) from top to bottom.

During certain conditions, such as iodine deficiency, the thyroid gland enlarges in order to capture more iodine from the blood to create thyroid hormones. The thyroid is supplied with blood through 4 major arteries. Under normal conditions these arteries carry the equivalent of the entire body’s supply of blood each hour.

Adjacent to each thyroid lobe is the laryngeal nerve which supplies the voice box and vocal cords. Because of this there is a risk of damage during thyroid surgeries.

Four parathyroid glands (near the thyroid) make parathyroid hormones (PTH). This causes the kidneys to retain calcium in the blood thus releasing phosphorus into the urine. PTH also increases the activation of Vit D which enhances the activity of Vit D & Calcium. Parathyroid glands are sometimes damaged in surgery or are accidentally removed leaving the patient to suffer from hypoparathyroidism for the rest of their life. This causes calcium levels to drop giving symptoms of muscle cramps & spasms, numbness and if severe, seizures.

Inside the thyroid are cells called follicular cells. They are arranged in ball shaped groups called follicles with the center (follicular lumen) containing stored thyroid hormone called a colloid. All of the thyroid follicles are contained in a fibrous capsule of the thyroid gland like bunches of grapes. The adjacent cells called parafollicular cells make additional hormones like calcitonin. The thyroid follicular cells have receptors (proteins) in the membrane for receiving hormones that control the thyroid like TSH (thyroid stimulating hormone – from the pituitary gland). TSH signals the NIS (sodium iodine symporters or pumps) to pull iodine into the cells to produce thyroid hormone.  TSH also signals the body to produce thyroglobulin which is used in the thyroid hormone creation process.