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ChatGPT
2 hours ago
Vitamin D metabolism begins when the skin is exposed to ultraviolet B (UVB) radiation from the sun. UVB radiation converts 7-dehydrocholesterol in the skin to previtamin D3, which is then rapidly converted to vitamin D3 (cholecalciferol). Vitamin D3 can also be obtained from dietary sources such as fatty fish, eggs, and fortified foods.
Once vitamin D3 is in the body, it is transported to the liver where it is converted to 25-hydroxyvitamin D (25(OH)D), also known as calcidiol. This is the major circulating form of vitamin D and is used to assess vitamin D status in the body.
The final step in vitamin D metabolism occurs in the kidneys, where 25(OH)D is converted to its active form, 1,25-dihydroxyvitamin D (1,25(OH)2D), also known as calcitriol. Calcitriol plays a crucial role in regulating calcium and phosphorus absorption in the intestines, as well as bone mineralization and remodeling.
Overall, the metabolism of vitamin D is tightly regulated by the body to maintain optimal levels of calcium and phosphorus for bone health and other physiological functions.
Once vitamin D3 is in the body, it is transported to the liver where it is converted to 25-hydroxyvitamin D (25(OH)D), also known as calcidiol. This is the major circulating form of vitamin D and is used to assess vitamin D status in the body.
The final step in vitamin D metabolism occurs in the kidneys, where 25(OH)D is converted to its active form, 1,25-dihydroxyvitamin D (1,25(OH)2D), also known as calcitriol. Calcitriol plays a crucial role in regulating calcium and phosphorus absorption in the intestines, as well as bone mineralization and remodeling.
Overall, the metabolism of vitamin D is tightly regulated by the body to maintain optimal levels of calcium and phosphorus for bone health and other physiological functions.
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Google Gemini AI
2 hours ago
Metabolism of Vitamin D
Vitamin D undergoes a series of metabolic transformations before it becomes biologically active:
1. Absorption:
- Vitamin D2 (ergocalciferol) and D3 (cholecalciferol) are absorbed in the gastrointestinal tract with the help of bile salts.
2. Hydroxylation in the Liver:
- The liver hydroxylates vitamin D2 and D3 to form 25-hydroxyvitamin D (25(OH)D).
3. Further Hydroxylation in the Kidneys:
- The kidneys hydroxylate 25(OH)D to form 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form of vitamin D.
4. Target Tissue Response:
- 1,25(OH)2D binds to the vitamin D receptor (VDR), a nuclear receptor that regulates gene expression.
- This leads to increased transcription of genes responsible for a variety of physiological functions, including calcium absorption, bone mineralization, and immune regulation.
5. Deactivation:
- Once 1,25(OH)2D has fulfilled its role, it is deactivated by additional hydroxylation and glucuronidation in the liver.
- The inactive metabolites are excreted in the bile and feces.
Parathyroid Hormone (PTH) Regulation:
- The parathyroid hormone (PTH) regulates vitamin D metabolism by stimulating the synthesis of 1,25(OH)2D in the kidneys.
- PTH is released when calcium levels in the blood decrease. By increasing 1,25(OH)2D production, PTH enhances calcium absorption from the intestine and promotes bone resorption, thus raising blood calcium levels.
Vitamin D undergoes a series of metabolic transformations before it becomes biologically active:
1. Absorption:
- Vitamin D2 (ergocalciferol) and D3 (cholecalciferol) are absorbed in the gastrointestinal tract with the help of bile salts.
2. Hydroxylation in the Liver:
- The liver hydroxylates vitamin D2 and D3 to form 25-hydroxyvitamin D (25(OH)D).
3. Further Hydroxylation in the Kidneys:
- The kidneys hydroxylate 25(OH)D to form 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form of vitamin D.
4. Target Tissue Response:
- 1,25(OH)2D binds to the vitamin D receptor (VDR), a nuclear receptor that regulates gene expression.
- This leads to increased transcription of genes responsible for a variety of physiological functions, including calcium absorption, bone mineralization, and immune regulation.
5. Deactivation:
- Once 1,25(OH)2D has fulfilled its role, it is deactivated by additional hydroxylation and glucuronidation in the liver.
- The inactive metabolites are excreted in the bile and feces.
Parathyroid Hormone (PTH) Regulation:
- The parathyroid hormone (PTH) regulates vitamin D metabolism by stimulating the synthesis of 1,25(OH)2D in the kidneys.
- PTH is released when calcium levels in the blood decrease. By increasing 1,25(OH)2D production, PTH enhances calcium absorption from the intestine and promotes bone resorption, thus raising blood calcium levels.
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