PTH-Vitamin D Axis

Increase PO4 - Phosphate (0.8-1.5 mmol/L**)** excretion (↓ in serum)
Increase Ca Calcium (2.2-2.5) reabsorption (↑ in serum)
Activate Calcitriol (1,25 VD) at the kidney → from 25-OH to 1,25-OH

Screenshot 2024-04-07 at 1.25.40 PM.png

Screenshot 2025-10-08 at 7.30.42 PM.png

<aside>

Calcitriol (1,25 VD) vs. PTH : Effect on PO4 and Ca

Ca (2+) → Net Increase with PTH (normal cases)

Molecule	PTH	Calcitriol (1,25 VD)
Kidney	↑ Ca re-absorption	↑ Ca
Intestine	NA	↑ Ca absorption
Bone	↑ Osteoclast, ↑ Ca	↑ Osteoclast, ↑ Ca

PO4 (3-) → Net decrease with PTH (normal cases)

Molecule	PTH	Calcitriol (1,25 VD)
Kidney	↓ PO4 (PTH dominant)	↑ PO4
Intestine	NA	↑ PO4 absorption
Bone	↑ Osteoclast, ↑ PO4	↑ Osteoclast, ↑ PO4
</aside>