The Parathyroid Gland By Jonah Carleton, & Elise Voorhis

Overview Thyroid Gland Parathyroid Gland Location Four rice grain sized glands located on/behind the thyroid gland Located in the center of the neck, at the back Behind the thyroid gland Top two are superior and bottom two are inferior Hormones Released Parathyroid Hormone (PTH) Function Stabilizes calcium and phosphorus levels PTH raises the level of calcium in the blood Breaks down bone, causing the release of calcium Not good for bones, but beneficial for other cells Makes it easier for body to absorb calcium from food Limits kidneys from excreting too much calcium Calcium not lost in urine Begins to produce calcitriol PTH decreases the level of phosphorus in the blood Calcitriol Helps the body absorb as much calcium as possible Regulated by Calcium Sensing Receptor (CaSR) The CaSR senses changes in blood calcium levels and releases PTH accordingly Thyroid Gland Parathyroid Gland

The Parathyroid Gland Operates in a Negative Feedback Loop Feedback loop for calcitonin and parathyroid hormone Calcitonin decreases blood calcium levels when they become too high Calcitonin is produced in the thyroid gland, but it is involved in a loop with PTH Parathyroid releases PTH when the blood calcium levels are too low Signaled by the Calcium Sensing Receptor (CaSR) Causes levels of calcium to increase Calcium taken out of the bones Increased PTH activates the vitamin D system (calcitriol system) Calcitriol is “active vitamin D” Vitamin D is converted into calcediol in the liver This calcediol is then turned into calcitriol in the kidneys This final transformation is regulated by PTH Parathyroid stops releasing PTH when the blood calcium levels are normal or too high Calcium signals to CaSR which conveys message to the Parathyroid

Hyperthyroidism Disease where a parathyroid is overactive and produces too much PTH Causes unusually high levels of calcium in the blood Due to overactive parathyroid Primary and Secondary forms Both usually cannot be prevented Vitamin D deficiency can lead to secondary hyperparathyroidism Too much calcium gets taken out of bones Weakens bones Can be either 1, 2, 3, or all 4 of the glands being hyperactive Very uncommon for 3 or 4 to by hyperactive (15-10%) Is more common as people get older Women are twice as likely to develop hyperparathyroidism as men Can be caused by overexposure of radiation Most cases sporadic 5% are inherited Is treated by surgery Enlargement of parathyroid gland called adenoma

Citations Campbell, Neil A., et al. Campbell Biology in Focus. Pearson Education Limited, 2017. “Parathyroid Glands: Function.” Function of the Parathyroid Glands, endocrinediseases.org/parathyroid/parathyroid_background.shtml. “Parathyroid Disorders.” Medlineplus, U.S. National Library of Medicine, medlineplus.gov/parathyroiddisorders.html. Kleerekoper, Michael. “About the Parathyroid Glands.” Empoweryourhealth, www.empoweryourhealth.org/endocrine- conditions/parathyroid. “Parathyroid Gland Introduction.” Parathyroid.com and Hyperparathyroidism, www.parathyroid.com/parathyroid.htm. Parathroid Gland - http://www.thyroidutah.com/thyroid-conditions/parathyroid-disorders/ Enlarged Gland -https://www.fairview.org/patient-education/40125 Feedback Loop- http://slideplayer.com/slide/3722522/