Parathyroid Glands
Anatomy: There are usually 4 parathyroid glands which consist of small epithelial bodies about 1-2 mm in length. Two glands are embedded in the cranial thyroid, the remaining 2 glands are located on the ventral trachea as near as the thoracic inlet in the connective tissue of the neck. They are difficult to find as they resemble small lymph nodes.
Secreting cells: These glands contain Chief (principal) cells.
Hormone: Parathyroid Hormone (PTH) aka Parathormone.
Target: PTH targets the bone tissue, kidneys and GIT.
Function: major regulator of the levels of calcium (Ca++), magnesium (Mg++) and phosphate (HPO) ions in the blood. Increase the number and activity of osteoclasts. The result is elevated bone reabsorption which releases ionic Ca++ and phosphates. Acts on the kidneys slowing the rate of Ca++ and Mg++ loss in urine. It also increases the loss of HPO in the urine and because of this it increases Ca++ and Mg++ in the blood. Promotes the formation of Calcitriol, the active form of vitamin D which increases the rate of Ca++, HPO, and Mg++ absorption from the GI tract into the blood.
Regulation: Blood calcium levels in a negative FB system. Low blood calcium levels stimulate PTH secretion which increases the level of Ca++ in the blood that does not involve the pituitary gland.
Clinical Disease: Vitamin D deficiency, Ca++ & P imbalance, hypocalcemia, Ricketts, osteomalacia
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