Structure and Function Thyroid and Parathyroid

The thyroid gland is located under the larynx in the neck and is the largest of all the endocrine glands. It has two wings (or lobes) joined by tissue called the isthmus that are wrapped around the trachea. The parathyroid glands are right behind the thyroid, with two on either side of the thyroid.

The thyroid gland is responsible for storing and making hormones that help regulate body temperature, blood pressure, heart rate, and how quickly food is turned into energy. The thyroid gland is made up of follicular and parafollicular epithelial cells that use iodine to secrete Triiodothyronine and Thyroxine, two hormones that are formed from the iodine and an amino acid called tyrosine . These hormones are responsible for stimulating all tissues in the body to make protein and increase oxygen used by the cells.

Triiodothyronine (referred to as T3 due to having 3 molecules of iodine attached to its molecular structure) makes up about 20% of all the hormones made by the thyroid, and is the most powerful even though it only has a lifespan of about 2 ½ days. It has an affect on almost every process in the body, and is needed by all organs and tissues (except for the testis and spleen) for energy and to increase oxygen. It forces the contractions of the heart, raises the heart rate, and impacts glucose metabolism.

Thyroxine (T4 – 4 iodine molecules are attached to its structure) is stored in between the thyroid cells in the follicle stems. T4 increases the activity and number of the mitochondria (energy generators) in the cells which increases the metabolic rate and revs the nervous system to increase activity of the endocrine system.

The production of both of these hormones are dictated by a hormone produced by the pituitary gland called TSH. The rate of production is related to the amount of TSH, if there is a higher number of the hormones active in the body, TSH production is less. If there is a low number present in the blood, the TSH is released to build the numbers back up.

The parathyroid glands are responsible for the amount of calcium in the blood due to the hormones parathormone and calcitonin. These hormones control calcium (which is needed for blood clotting, nerve functions, secretion of the glands, and muscle connections) and phosphate levels in the blood and help with bone formation. The calcitonin promotes cells called osteoblasts that are responsible for growing new bone, and hinders the osteoblasts that break down bone. The parathyroid secretions also affect how much calcium is saved by the kidneys and how much food is absorbed by the intestines.

The impact that these glands and the hormones they produce have on our bodies makes them vital to our health because of all the important functions they perform in regulating and protecting different substances that our bodies require to be healthy.  Thyroid conditions are serious illnesses that should be addressed as soon as possible.  Proper treatment can minimize the affects of these conditions, and allow a person to continue to live a healthy life. (2011) Thyroid Hormone Triiodothyronine Retrieved from

UMMC (2010) Endocrinology Health Guide The Thyroid Gland Retrieved from