Rav Endocrinology Parathroid Pth

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PTH, secreted by the parathyroid glands, has several actions, the most important of which is to prevent hypocalcemia.Parathyroid cells sense decreases in the level of serum ionized calcium via

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Parathyroid cells sense decreases in the level of serum ionized calcium via the calcium-sensing receptor, which lies in the cell membrane of parathyroid cells.

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Hypocalcemia leads to decreased

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Hypocalcemia leads to decreased binding of calcium to the calcium-sensing receptor, with resultant release of preformed PTH into the circulation.

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PTH increases the serum calcium level within minutes by

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PTH increases the serum calcium level within minutes by increasing renal and intestinal absorption of calcium and by rapidly mobilizing calcium and phosphate from bone (bone resorption).

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PTH enhances distal tubular calcium...

PTH also decreases

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PTH enhances distal tubular calcium reabsorption. PTH also decreases renal phosphate reabsorption and thus increases urine phosphate losses.

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Urine phosphate loss prevents the solubility product of calcium and phosphate from

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Urine phosphate loss prevents the solubility product of calcium and phosphate from being exceeded in serum as calcium levels rise in response to PTH

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PTH also increases the serum calcium level by upregulation of the 1α-hydroxylase enzyme, which stimulates

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PTH also increases the serum calcium level by upregulation of the 1α-hydroxylase enzyme, which stimulates conversion of vitamin D to its most active form, 1,25-dihydroxy vitamin D; this form of vitamin D increases the percentage of dietary calcium absorbed by the intestine.

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Vitamin D3 is derived from

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Vitamin D3 is derived from dietary sources and by skin exposure to ultraviolet light, which converts cholesterol precursors to vitamin D3, which in turn is converted in the liver to 25-hydroxy vitamin D. This form, in turn, subsequently undergoes 1α-hydroxylation in the proximal renal tubular cells to become 1,25-dihydroxy vitamin D. Measurement of serum 25-hydroxy vitamin D is the best indicator of total vitamin D body stores because of its long half-life.

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the best indicator of total vitamin D body

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Measurement of serum 25-hydroxy vitamin D is the best indicator of total vitamin D body stores because of its long half-life.

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Long-term increases in PTH secretion generally result in

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Long-term increases in PTH secretion generally result in bone resorption by inhibiting osteoblast function and promoting osteoclast activity.

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important regulators of bone growth and bone remodeling

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PTH and 1,25-dihydroxy vitamin D both function as important regulators of bone growth and bone remodeling.

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Testing of parathyroid function includes measuring

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Testing of parathyroid function includes measuring circulating intact PTH levels by radioimmunoassay.

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The most appropriate management for this patient’s severe osteoporosis his patient has adequate calcium and vitamin D intake; therefore, her bisphosphonate therapy is not working adequately.

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The most appropriate management for this patient’s severe osteoporosis is to discontinue the alendronate and start teriparatide (recombinant human parathyroid hormone [1-34]). This patient has adequate calcium and vitamin D intake; therefore, her bisphosphonate therapy is not working adequately. Teriparatide, one of the few available therapies that stimulates new bone formation, is given via daily subcutaneous injection for a recommended duration of 1 to 2 years. Teriparatide can significantly decrease the incidence of both vertebral and nonvertebral fracture

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Because animal studies have shown an increased risk of osteosarcoma, this agent teriparatide should be avoided in t

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Because animal studies have shown an increased risk of osteosarcoma, this agent should be avoided in patients with Paget disease of bone, previous radiation therapy involving the skeleton, or a history of skeletal cancer.

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Teriparatide should be considered in patients who are

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Teriparatide should be considered in patients who are intolerant of other medications, are not responding to first-line therapy, or have the greatest fracture risk. Trials, however, have shown no benefit of concurrent teriparatide and bisphosphonate therapy, so adding teriparatide to her current regimen is inappropriate.

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Serum calcium levels should be monitored in immobilized patients to check for the development of

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Objective:Diagnose hypercalcemia caused by immobilization.
Key Point

* Serum calcium levels should be monitored in immobilized patients to check for the development of hypercalcemia of immobilization, which is more likely to occur in patients with high bone turnover, such as young patients and patients with Paget disease.

This patient has hypercalcemia most likely