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- What are the differences between calcium and phosphate homeostasis?
The differences between calcium and phosphate homeostasis are enlisted in the
table given below.Parameters Calcium Phosphorous
Distribution
Bone 99 % 85 %
Non-osseous tissue <1 % 15 %
Extracellular: intracellular 10,000:1 1:1–2
Protein binding 50 % 12 %
Diurnal variation Almost nil Nadir between 0800 and 1100h
Influence of meal on serum level No change Decrease
Intestinal absorption Duodenum and
jejunumDuodenum and jejunumActive 70–90 % 20–30 %
Passive 8–20 % 60–70 %
Renal reabsorption
PCT 60–70 % 85 %
TALH 20 % Nil
DCT and CT 8–10 % 15 %
Key organs in homeostasis Bone and intestine Kidney
Prime hormonal regulator PTH and 1,25
(OH) 2 DPTH and FGF-23Bone mineralization Important Essential- What is the most important mineral for bone mineralization?
Bone mineralization is a coordinated process which involves deposition of cal-
cium, phosphate, and magnesium on matrix, laid down by osteoblasts. Optimal
levels of serum calcium, phosphate, PTH, 1,25(OH) 2 D, bone-specific alkaline
phosphatase, pH, and FGF-23 are required for bone mineralization. The solu-
bility product of calcium and phosphate is the major determinant of bone min-
eralization rather than the serum level of individual minerals, calcium, or
phosphate. Minor alterations in serum phosphate concentration lead to marked
variation in the solubility product, whereas minor alterations in serum calcium
do not significantly influence the same. Hence, the most important metabolite
for mineralization is phosphate not calcium. This is best evidenced in patients
with hypophosphatemic osteomalacia, who have impaired mineralization
despite normal serum calcium level.- What is FGF- 23?
FGF-23 is a 251 amino acid peptide predominantly secreted by osteocytes. It is
a major phosphatonin (possibly a misnomer as it is a phosphaturic hormone)5 Rickets–Osteomalacia