Vitamin D Metabolism and Physiological Functions
Vitamin D Metabolism and Physiological Functions
The Life Cycle from Precursor to Active Form
🟢 Sources
☀️ Skin Synthesis
UVB (Ultraviolet B) Exposure
7-Dehydrocholesterol (Precursor)
→
Vitamin D₃ (Cholecalciferol)
🐟 Diet and Supplements
Intake of Vitamin D₂/D₃
Fish, Egg Yolk, Fortified Milk
→
Vitamin D
⬇️ Enters Bloodstream
🔄 Activation Pathway
🔬 Step 1: Liver
First Hydroxylation (25-Hydroxylase)
Vitamin D₃ $\to$ 25-Hydroxyvitamin D₃ (Calcidiol)
⬇️ Transport
💧 Step 2: Kidney
Second Hydroxylation (1α-Hydroxylase)
25-Hydroxyvitamin D₃ $\to$ 1,25(OH)₂D₃ (Active Form)
🌟 Functions of Active Vitamin D (1,25(OH)₂D₃)
🍽️
Intestine
Endocrine Action
↑ Calcium and Phosphate Absorption
🦴
Bone
Endocrine Action
↑ Bone Metabolism & Mineralization
🩸
Pancreas
Endocrine Action
↑ Insulin Secretion
🛡️
Cellular and Immune System
Autocrine & Paracrine Action
Regulates Proliferation, Differentiation, and Immunity
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