Parathyroid glands
These glands lie on either side of the thyroid gland and secrete the hormone /Janithonnone (Eig. 6.1). Secretion is dependent on the Ievelsof calcium in the blood - if levels are low.
calcium is resorbed from the bones and absorption of calcium from the intestine is increased I Eig. 6.2).Oversecretion (IijjperiMirtiiIiifroidisni) occurs in:
PriiiitiriJ hyperparathyroidism - due to neoplasia of the parathyroid glands. This causes bone resorption, bone weakness and pathological fractures.
Seeondary hy∣>erparat Iiyroidism - as seen in chronic renal failure. The Calciunvphosphate ratio in the blood is altered by impaired kidney function. This leads to increased output of parathormone and consequently increased resorption of bone in an effort to maintain bloιxl calcium levels. There is preferential resorption from the mandible and maxilla, producing a condition known as ‘rubber jaw’ - the jaw becomes pliable and fragile and the teeth mav fall out.
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NiilriHontd hyperparathyroidism - results from feeding low calcium diets, e.g. all meat diet. Parathormone is produced in an attempt to raise the blood calcium levels by bone resorption.