The unit of blood calcium and blood phosphorus is molar concentration (mol/L), the original unit is percent milligrams (mg/dl), the unit used for calcium and phosphorus product is percent milligrams, so it is necessary to convert the molar concentration to percent milligrams. The relationship between the two is: Calcium: 1mg/dl = 0.25mmol/L, i.e. 1mmol/L = 4mg/dl; Phosphorus: 1mg/dl = 0.3229mmol/L, i.e. 1mmol/L = 3.1mg/dl. Blood calcium refers to the calcium contained in the plasma, which is 9-11mg/dl on average. calcium) and nondiffusible calcium. Non-diffusible calcium refers to calcium bound to plasma proteins (mainly albumin). It does not readily cross capillary walls. Diffusible calcium is mainly free Ca2+ and a small amount of soluble calcium salts bound to citric acid or other acids (Table 12-1). Table 12-1 Content of various components of plasma calcium in normal subjects mg/100 ml Protein-bound calcium Citrate Other unspecified calcium Total mg equivalent/liter 4.56 0.17 0.32 9.93 % of total 2.28 0.08 0.16 4.96 Ca2+ 46.0 CaPO4 1.7 3.2 100.0 4.270.16 0.08 2.36 1.6 47.5 The main physiological role is played by free Ca2+, and there is a dynamic equilibrium between Ca2+ a protein-bound calcium and small-molecule-bound calcium in plasma. This balance is influenced by the plasma pH. When the blood is acidic, the concentration of free Ca2+ increases; conversely, when the blood is alkaline, the concentration of protein-bound calcium increases and the concentration of free Ca2+ decreases. Therefore, clinically, alkalosis is often accompanied by convulsions, which are associated with low blood calcium. In plasma, 80-85% of phosphorus is present in the form of HPO4. 15-20% is present in the form of H2PO4-, while the amount of PO43- is very small. The product of the two ([Ca] × [P]) is 30-40. When ([Ca] × [P]) > 40, calcium and phosphorus are deposited in bone tissue in the form of bone salts; if ([Ca] × [P]) < 35, it prevents bone calcification, and can even make bone salts dissolve, affecting the role of osteogenesis.