Factors Affecting Plasma Calcium Level

Factors affecting plasma calcium level are as follows:

  1. Amount of Ca absorbed from the gastrointestinal tract: This is influenced by many factors as given below:

  2. Parathyroid hormone: In addition to its effect of increase intestinal absorption of Ca, it also mobilizes one Ca++ and causes a marked hypercalcemia.

  3. Inverse relationship between plasma Ca and Inorganic P Levels: When plasma Ca rises, the plasma inorganic P level falls and vice versa. In this way, the product of serum Ca and inorganic P (both in mg per 100 ml) remains constant at 30 to 40 in the adult and 40 to 55 in children. Plasma Ca level falls in kidney disease due to reaction of phosphate which leads to a high plasma inorganic phosphate level.

  4. Serum protein level: Each gram of serum protein binds 0.84 mg of Ca. Thus a decrease in serum protein level (i.e. hypoproteinemia) will result in a decreased level of bound Ca and will also result in a lowered total serum Ca. Because the ionized serum Ca remains normal, therefore such a person will not suffer from tetany because it is only the ionized Ca which is physiologically active.

  5. Renal excretion: Normally only a small part of Ca lost from the body is excreted in urine. But if excessive amounts of Ca are administered, more Ca is excreted in urine. Renal loss of Ca is also increased if more Na+ is being excreted in urine, e.g. by diuretics.

  6. Calcitonin: It is a hormone which now called thyrocalcitonin as it is produced by the parafollicular cells (also called clear or C cells) of the thyroid gland. There is evidence that these cells are also present in the substance of the parathyroid glands. Its release increases in response to hypercalcemia. It tends to lower the serum Ca level as it antagonizes the action of the parathyroid hormone. Calcitonin decreases bone reabsorption and increases the deposition of Ca in bones. It is a polypeptide with 32 amino acids and has been synthesized. It has been successfully used in treating Paget’s disease of the bone.