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What are the two main mineral constituents of bone?
What are the two main mineral constituents of bone?
What is the approximate percentage of calcium found in the human adult's bones?
What is the approximate percentage of calcium found in the human adult's bones?
98%
What is the primary function of osteoclasts?
What is the primary function of osteoclasts?
Where does the majority of calcium and phosphate absorption occur in the digestive system?
Where does the majority of calcium and phosphate absorption occur in the digestive system?
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The parathyroid hormone (PTH) directly stimulates osteoclasts, leading to bone resorption.
The parathyroid hormone (PTH) directly stimulates osteoclasts, leading to bone resorption.
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What is the primary function of vitamin D in relation to bone mineral homeostasis?
What is the primary function of vitamin D in relation to bone mineral homeostasis?
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What is the active metabolite of vitamin D?
What is the active metabolite of vitamin D?
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Which hormone is secreted by the parafollicular cells of the thyroid gland?
Which hormone is secreted by the parafollicular cells of the thyroid gland?
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What is the effect of calcitonin on osteoclast activity?
What is the effect of calcitonin on osteoclast activity?
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Glucocorticoids promote bone formation.
Glucocorticoids promote bone formation.
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Which of the following medications is primarily used to treat hypercalcemia of malignancy?
Which of the following medications is primarily used to treat hypercalcemia of malignancy?
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Denosumab acts by inhibiting the activity of parathyroid hormone (PTH).
Denosumab acts by inhibiting the activity of parathyroid hormone (PTH).
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What is the mechanism of action of cinacalcet, a calcimimetic drug?
What is the mechanism of action of cinacalcet, a calcimimetic drug?
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Thiazide diuretics promote calcium excretion in the kidneys.
Thiazide diuretics promote calcium excretion in the kidneys.
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Which of the following is not a potential adverse effect of fluoride treatment for osteoporosis?
Which of the following is not a potential adverse effect of fluoride treatment for osteoporosis?
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Strontium ranelate primarily works by promoting bone formation.
Strontium ranelate primarily works by promoting bone formation.
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In patients with chronic kidney disease (CKD), what is the primary reason for deficient 1,25(OH)2D production?
In patients with chronic kidney disease (CKD), what is the primary reason for deficient 1,25(OH)2D production?
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What is the primary characteristic differentiating idiopathic hypercalciuria from other types of hypercalcemia?
What is the primary characteristic differentiating idiopathic hypercalciuria from other types of hypercalcemia?
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In patients with nephrotic syndrome, what is the primary issue contributing to low vitamin D levels?
In patients with nephrotic syndrome, what is the primary issue contributing to low vitamin D levels?
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Paget's disease of bone is usually categorized as a systemic bone disorder affecting multiple bones simultaneously.
Paget's disease of bone is usually categorized as a systemic bone disorder affecting multiple bones simultaneously.
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What is the mechanism by which high levels of oxalate are absorbed in patients with enteric oxaluria?
What is the mechanism by which high levels of oxalate are absorbed in patients with enteric oxaluria?
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What is the most common treatment for Paget's disease?
What is the most common treatment for Paget's disease?
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Hypophosphatemia can be caused by increased levels of biologically active FGF23.
Hypophosphatemia can be caused by increased levels of biologically active FGF23.
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Which of the following is NOT a common symptom of hypocalcemia?
Which of the following is NOT a common symptom of hypocalcemia?
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In patients with osteitis fibrosa, the parathyroid hormone (PTH) is not acting on the kidneys.
In patients with osteitis fibrosa, the parathyroid hormone (PTH) is not acting on the kidneys.
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Which of the following is a common cause of hypercalcemia in chronic kidney disease (CKD)?
Which of the following is a common cause of hypercalcemia in chronic kidney disease (CKD)?
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Idiopathic infantile hypercalcemia is always a genetic disorder.
Idiopathic infantile hypercalcemia is always a genetic disorder.
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Which of the following medications is considered a treatment option for idiopathic hypercalciuria?
Which of the following medications is considered a treatment option for idiopathic hypercalciuria?
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Osteoporosis is always caused by low estrogen levels, primarily due to menopause.
Osteoporosis is always caused by low estrogen levels, primarily due to menopause.
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A patient presents with bone pain, increased alkaline phosphatase levels, and characteristic findings on radiologic imaging. What is the most likely diagnosis?
A patient presents with bone pain, increased alkaline phosphatase levels, and characteristic findings on radiologic imaging. What is the most likely diagnosis?
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What is the primary role of FGF23 in maintaining mineral homeostasis?
What is the primary role of FGF23 in maintaining mineral homeostasis?
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Study Notes
Bone Mineral Homeostasis
- Bone is the primary storage site for calcium and phosphorus
- Bone serves as structural support and site of hematopoiesis
- Calcium and phosphate are essential for cellular function
- Calcium and phosphate homeostasis is regulated by hormones
Principal Hormonal Regulators
-
Parathyroid Hormone (PTH):
- A single-chain peptide hormone (84 amino acids)
- Produced in the parathyroid gland
- Functions to increase serum calcium and decrease serum phosphate
- Stimulates osteoclast activity, increasing bone resorption
- Increases calcium and phosphate reabsorption in the kidneys
-
Vitamin D (1,25-dihydroxyvitamin D):
- Active metabolite of vitamin D
- Increases calcium absorption from the intestine and increases calcium reabsorption in the kidneys
Secondary Hormonal Regulators
-
Calcitonin:
- Secreted by the parafollicular cells of the thyroid gland
- Decreases serum calcium and phosphate by inhibiting osteoclast activity
-
Estrogens:
- Prevent accelerated bone loss and increase bone formation
- Important in preventing postmenopausal osteoporosis
Nonhormonal Agents Affecting Bone Mineral Homeostasis
-
Bisphosphonates:
- Inhibit hydroxyapatite crystal formation/dissolution
- Used to treat Paget's disease, hypercalcemia, and osteoporosis
- Common side effect: esophageal and gastric irritation
-
Denosumab:
- RANKL inhibitor
- Reduces bone resorption; used for osteoporosis and certain cancers
- Administered subcutaneously every 6 months
-
Calcimimetics (e.g., cinacalcet):
- Modulate the calcium-sensing receptor
- Inhibit Parathyroid hormone secretion, used for secondary hyperparathyroidism
Abnormal Serum Calcium & Phosphate Levels
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Hypercalcemia: High serum calcium
- Causes: Hyperparathyroidism, cancer, hypervitaminosis D, sarcoidosis, thyrotoxicosis
- Management: Saline diuresis, bisphosphonates, calcitonin, glucocorticoids
-
Hypocalcemia: Low serum calcium
- Causes: Hypoparathyroidism, vitamin D deficiency, malabsorption, medications
- Management: Calcium supplements, vitamin D, parathyroid hormone (PTH)
Abnormal Serum Calcium & Phosphate Levels continued
-
Hyperphosphatemia: High serum phosphate
- Causes: Renal failure, excessive phosphate intake
- Management: Phosphate binders, dialysis
-
Hypophosphatemia: Low serum phosphate
- Causes: Vitamin D deficiency, malnutrition, diuretics
- Management: Phosphate supplements
Other Disorders of Bone Mineral Homeostasis
- Paget's disease of bone: Uncontrolled osteoclastic bone resorption followed by disorganized bone formation
- Osteoporosis: Bone mineral density loss, leading to increased fracture risk
- Intestinal oxaluria: Elevated urine oxalate levels in patients with short bowel syndromes or fat malabsorption, potentially leading to calcium oxalate kidney stones.
Other Topics
- Vitamin D: Is a precursor to several biologically active metabolites. Converted in liver to 25-OH-D3, then to 1,25(OH)2D3 (calcitriol)
- FGF23: Inhibits 1,25-dihydroxyvitamin D3 production; increased levels in patients with chronic kidney disease, causing secondary hyperparathyroidism.
- Other substances (e.g. PTHrp, RANK, RANKL, osteocalcin, calcitonin) act in the complex process of bone mineral homeostasis.
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Description
This quiz covers the critical aspects of bone mineral homeostasis, focusing on the roles of calcium and phosphorus. It also explores the principal hormonal regulators such as Parathyroid Hormone and Vitamin D, as well as secondary regulators like Calcitonin. Understand how these hormones impact bone health and mineral balance in the body.
