Parathyroid hormone (PTH) plays a crucial role in activating vitamin D. In the kidneys, PTH stimulates the enzyme 1α-hydroxylase in the proximal tubules. This enzyme converts the inactive storage form of vitamin D, 25-hydroxyvitamin D (calcidiol), into the active hormonal form, 1,25-dihydroxyvitamin D (calcitriol). Calcitriol then acts on the intestines to increase the absorption of dietary calcium and phosphate, and on bone to work synergistically with PTH to mobilize calcium. This is a key part of PTH's strategy to raise blood calcium: it directly stimulates bone resorption and renal calcium reabsorption, and indirectly increases intestinal absorption via vitamin D activation. PTH also decreases phosphate reabsorption in the kidney, preventing hyperphosphatemia when calcium levels rise.

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Zambia

• Joseph Soko – 101 pts

• Visual Pathway Lesions
• Positive and Negative Symptoms
• Hallucinations and Delusions
• Antipsychotic Medications
• Emergency: Environmental Emergencies