Term
| Where do you get 1,25 DHCC from? |
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Definition
| It is a metabolite of vitamin D3. |
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Term
| What are the 2 main methods of acquiring vitamin D? |
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Definition
| Ingestion and production requiring cholesterol and UV radiation. |
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Term
| What enzyme in the kidney is responsible for turning 25 HCC into 1, 25 DHCC? |
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Definition
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Term
| What are the actions of 1, 25 DHCC? |
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Definition
1) It stimulates absorption of CA2+ from the intestine
2) It increases tubular reabsorption of Ca 2+ in the kidney
3) It promotes the action of PTH in bone. |
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Term
| How does 1, 25 DHCC work in the GI tract? |
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Definition
| It induces the production of intracellular Ca2+ binding proteins which buffer Ca2+. |
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Term
| Where is calcitonin synthesised? |
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Definition
| It is synthesised and secreted by the parafollicular cells (C cells) of the thyroid gland. |
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Term
| How does calcitonin work? |
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Definition
1) It acts to inhibit osteoclast motility and cell shape inactivating them. This causes a rapid fall in Ca2+ caused by the inhibition of bone resorption
2) Decreases tubular reabsorption of CA2+ in the kidney. |
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Term
| Describe the features of osteoporosis. |
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Definition
1) Reduced bone density and mass
2) Equal loss of mineral and organic matrix
3) Increased risk of fractures. |
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Term
| What is the pathogenesis of osteoporosis? |
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Definition
| Bone resorption exceeds formation. |
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Term
| What treatment options are available for osteoporosis? |
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Definition
1) Estrogen replacement
2) Anti-resorptive drugs (bisphosphinates, calcitonin etc.)
3) Replace sex steroids (androgens in men)
4) Calcium and vitamin D in the diet
5) Exercise
6) Reduce risk factors. |
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Term
| What is the cause of osteomalacia? |
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Definition
| Inadequate mineralisation of new bone matrix. |
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Term
| What is the most common cause of osteomalacia or rickets? |
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Definition
| Hypocalcaemia. Can be a metabolic issue (1, 25 DHCC inactive or cannot be produced). |
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Term
| What is vitamin D-dependant rickets type II? |
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Definition
| A mutation in the 1, 25 DHCC receptor. |
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Term
| What are the treatment options for osteomalacia? |
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Definition
1) Vitamin D analogs
2) Diet
3) Treat malabsorption. |
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Term
| What are the key symptoms of mild and moderate hypercalcaemia? |
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Definition
1) Mild hypercalcaemia may present without symptoms
2) Moderate hypercalcaemic patients usually present with symptoms of neuromuscular suppression. |
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Term
| What is primary hyperparathyroidism? |
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Definition
| Ca2+ homeostatic loss due to excessive PTH secretion. Excess PTH could be secreted from a benign parathyroid tumour (adenoma) or hyperplastic parathyroid tissue. |
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Term
| How can you treat hypercalcaemia? |
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Definition
1) Antiresorptive agents (bisphosphates and salmon calcitonin)
2) Surgery:
- Removal of the adenoma
- Removal of the majority of all 4 glands in hyperplasia. |
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