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What is partially embedded in the posterior surface of the lateral lobes of the thyroid gland, several small, round masses of tissue.
parathyroid glands
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What are the 2 types of epithelial cells in the parathyroid glands?
the more numerous are the chief (principal) cells
the other is the oxyphil cell
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What is the function of the chief cell of the parathyroid glands?
They produce parathyroid hormone PTH
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What is the function of the oxyphil cells of the parathyroid glands?
the function is not known
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What hormone is the major regulator of the levels of calcium (Ca2+), magnesium (Mg2+), and phosphate (HPO4,2-)ions in the blood?
parathyroid hormone (PTH)
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What is the specific action of PTH?
To increase the # and activity of osteoclasts
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What is the result when PTH increases the # & activity of osteoclasts?
elevated bone resorption, which releases ionic calcium and phosphates into the blood.
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PTH also acts on the....
Kidneys
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How does PTH act on the kidneys?
1. It slows the rate at which Ca2+ and MG2+ are lost from blood into the urine
2. it increases loss of HPO4,2- from blood into the urine
*Because more HOP4,2- is lost in the urine than is gained from the bones, PTH decreases blood HOP4,2- level and increases blood Ca2+ and Mg2+ levels.
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PTH also promotes the formation of the hormone _____ in the kidneys, the active form of vitamin D.
calcitriol
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The blood calcium level directly controls the secretion of both _____ and ____ hormone via negative feedback loops that do not involve the pituitary gland
calcitonin and parathyroid hormone
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What is the 6 steps of calcium level directly controlling the secretion of calcitonin and parathyroid hormone?
1. A higher than normal level of calcium ions in the blood stimulates parafollicular cells of the thyroid gland to release more calcitonin.
2. Calcitonin inhibits the activity of osteoclasts, thereby decreasing the blood Ca2+ level.
3. a lower than normal level of Ca2+ in the blood stimulates chief cells of the parathyroid gland to release more PTH
4. PTH promotes resorption of bone extracellular matrix, which releases Ca2+ into the blood and slows loss of Ca2+ in the urine, raising the blood level of Ca2+.
5. PTH also stimulates the kidneys to synthesize calcitriol, the active form of vitamin D.
6. Calcitriol stimulates increased absorption of Ca2+ from foods in the gastrointestinal tract, which helps increase the blood level of Ca2+.
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