Calcium and Phosphorus Homeostasis
Start with the big picture
Most body calcium and phosphate is stored in bone as hydroxyapatite, while circulating levels reflect a balance among absorption, kidney reabsorption or excretion, and bone remodeling. PTH increases renal calcium reabsorption and promotes phosphate loss, while stimulating calcitriol synthesis. Calcitriol enhances intestinal absorption of both minerals; FGF23 lowers phosphate by reducing renal reabsorption and calcitriol production. Calcitonin can reduce osteoclastic activity, with a minor acute effect on serum levels. Calcium is present in bound and ionized forms, and acid–base status can shift the ionized fraction. The lesson also connects magnesium status, dietary balance, and PTH signaling to mineral homeostasis.
What you'll learn
- Describe the distribution of calcium and phosphate between bone and other body compartments.
- Compare the effects of PTH, calcitriol, calcitonin, and FGF23 on mineral balance.
- Explain how intestinal absorption and renal handling contribute to calcium and phosphate homeostasis.
- Relate albumin binding, acid–base status, and magnesium to calcium regulation.
- Summarize how bone remodeling and feedback mechanisms integrate mineral control.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
