Vitamin D (calciferol): Sources, Synthesis, Metabolism, Functions, Deficiency || #Usmle biochemistry
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Vitamin D (calciferol): Sources, Synthesis, Metabolism, Functions, RDA, Regulation and Deficiency
Vitamin D (calciferol)
Characteristics
-------------------------
Active form: 1,25-dihydroxyvitamin D (1,25-(OH)2 D3, calcitriol)
Sources:
--------------
Ergocalciferol (vitamin D2): mushrooms, fortified foods (e.g., milk, breakfast cereals, formula), yeast (from ergosterol)
Cholecalciferol (vitamin D3)
Synthesized in the skin (stratum basale) when exposed to UV light
Fortified foods (e.g., milk, breakfast cereals, formula), fatty fish (liver), egg yolks
Vitamin D synthesis
--------------------------------
Liver: cholesterol → 7-dehydrocholesterol (provitamin D3)
Enzyme: cholesterol dehydrogenase
Skin
Storage of 7-dehydrocholesterol
Cleavage of 7-dehydrocholesterol via irradiation with UV light → cholecalciferol (in the stratum basale of the skin)
Liver: hydroxylation of cholecalciferol to 25-hydroxyvitamin D (25-OH D3, calcidiol; activated vitamin D2)
Kidneys: 1α-hydroxylase hydroxylates 25-hydroxyvitamin D → 1,25-dihydroxyvitamin D
Transport to target cells: vitamin D-binding protein (DBP)
Storage: mainly in adipose tissue as 25-hydroxycholecalciferol
Regulation of vitamin D synthesis: via regulation of 1α-hydroxylase activity in proximal convoluted tubule
↓ Calcium, ↓ phosphate, and ↑ PTH → ↑ 1α-hydroxylase activity → ↑ 1,25-dihydroxyvitamin D biosynthesis
↑ Calcium, ↑ phosphate, and ↑ 1,25-dihydroxyvitamin D → ↓ 1α-hydroxylase activity → ↓ 1,25-dihydroxyvitamin D biosynthesis
#vitamind #vitamindbiochemistry #vitamindsources #vitamindbenefits #vitamindsynthesis #vitamindfunctions #vitamindfoods #vitaminddosage #vitaminDrichfoods #vitamindfoods #vitaminDbiology #vitamindmetabolism #vitaminDusmle #vitamindvideo #vitamindlecture #vitamindanimation
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Vitamin D (calciferol): Sources, Synthesis, Metabolism, Functions, RDA, Regulation and Deficiency
Vitamin D (calciferol)
Characteristics
-------------------------
Active form: 1,25-dihydroxyvitamin D (1,25-(OH)2 D3, calcitriol)
Sources:
--------------
Ergocalciferol (vitamin D2): mushrooms, fortified foods (e.g., milk, breakfast cereals, formula), yeast (from ergosterol)
Cholecalciferol (vitamin D3)
Synthesized in the skin (stratum basale) when exposed to UV light
Fortified foods (e.g., milk, breakfast cereals, formula), fatty fish (liver), egg yolks
Vitamin D synthesis
--------------------------------
Liver: cholesterol → 7-dehydrocholesterol (provitamin D3)
Enzyme: cholesterol dehydrogenase
Skin
Storage of 7-dehydrocholesterol
Cleavage of 7-dehydrocholesterol via irradiation with UV light → cholecalciferol (in the stratum basale of the skin)
Liver: hydroxylation of cholecalciferol to 25-hydroxyvitamin D (25-OH D3, calcidiol; activated vitamin D2)
Kidneys: 1α-hydroxylase hydroxylates 25-hydroxyvitamin D → 1,25-dihydroxyvitamin D
Transport to target cells: vitamin D-binding protein (DBP)
Storage: mainly in adipose tissue as 25-hydroxycholecalciferol
Regulation of vitamin D synthesis: via regulation of 1α-hydroxylase activity in proximal convoluted tubule
↓ Calcium, ↓ phosphate, and ↑ PTH → ↑ 1α-hydroxylase activity → ↑ 1,25-dihydroxyvitamin D biosynthesis
↑ Calcium, ↑ phosphate, and ↑ 1,25-dihydroxyvitamin D → ↓ 1α-hydroxylase activity → ↓ 1,25-dihydroxyvitamin D biosynthesis
#vitamind #vitamindbiochemistry #vitamindsources #vitamindbenefits #vitamindsynthesis #vitamindfunctions #vitamindfoods #vitaminddosage #vitaminDrichfoods #vitamindfoods #vitaminDbiology #vitamindmetabolism #vitaminDusmle #vitamindvideo #vitamindlecture #vitamindanimation
4 سال پیش
در تاریخ 1399/01/25 منتشر شده
است.
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