fosfatabsorpsjon

fosfatabsorpsjon refers to the biological process by which phosphate ions are taken up from the extracellular environment into cells, primarily occurring in the intestines, kidneys, and bone. In the small intestine, dietary phosphate is absorbed through both passive paracellular transport and active transcellular transport mediated by sodium‑dependent phosphate transporters (NaPi‑2b) found along the villi. The efficiency of intestinal absorption is influenced by dietary calcium, vitamin D status, and acid-base balance; for example, vitamin D upregulates NaPi‑2b expression, enhancing phosphate uptake.

In the kidneys, phosphaturic hormones such as parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) regulate phosphate reabsorption in the proximal tubule by modulating NaPi‑2a and NaPi‑2c transporters. When PTH or FGF23 levels rise, phosphate reabsorption decreases, promoting phosphaturia. This renal mechanism is critical for maintaining systemic phosphate homeostasis, which is essential for bone mineralization, energy metabolism, and cell signaling.

Phosphate homeostasis involves a tight feedback loop between intestinal absorption, renal excretion, and bone storage. Dysregulation can lead to disorders such as hypophosphatemia, osteomalacia, or hyperphosphatemia associated with renal disease and secondary hyperparathyroidism. Understanding fosfatabsorpsjon is therefore important for diagnosing and managing these conditions.