Calcium Distribution:
The adult body has approximately 1200g of calcium 90% of it is combined as the salt to give hardness to the bones and teeth. The bones provide the hard framework for the body and they also furnish the reserves of calcium to the circulation to maintain the plasma level of calcium constant at all times.
The remaining 1% of the calcium in adults, which is about 10-12 g is distributed throughout the extracellular and intra-cellular fluids of the body.
Functions of Calcium:
Calcium is required for a number of important functions:
1. Activates a number of enzymes like pancreatic lipase, adenosine triphosohatase and some proteolytic enzymes.
2. Is required for the synthesis of acetylcholine, substance necessary for transmission of nerve impulses.
3. Increases the permeability of cell membranes, thus helping in the absorptive process.
4. Aids in the absorption of vitamin B12 from the ileum.
5. Regulates the contraction and relaxation of muscles, including the heart beat.
6. Catalyzes several steps in the clotting of blood. The blood coagulation protein prothrombin is converted from its inactive form to the active form thrombin which then catalyses the conversion of the next coagulation protein in the sequence.
Calcium Absorption:
Calcium absorption is favored by certain factors in the body and is hindered by certain factors.
Factors of Calcium Absorption:
1. Body need is the major factor governing the absorption of calcium. Healthy adults receiving a balanced diet absorb approximately 30-40% of their dietary calcium. At higher levels of intake, the proportion that is absorbed is lower. On the contrary, if the dietary supply of calcium is low, the body absorbs a high proportion of the intake.
During growth the absorption is increased to take care of increase in size and hardness of the bones. Thus, children absorb proportionally more calcium than adults. During pregnancy and lactation as well when body requirements are more absorption increases.
2. Vitamin D and parathyroid hormone also control calcium absorption. When the blood calcium level decreases, PTH is secreted. One of its functions is to stimulate the kidneys to synthesize calcitriol, the active form to vitamin D. This stimulates increased absorption from the intestines and together with PTH, enhances mobilization of the bone store of calcium.
3. An acid medium helps in the absorption of calcium because calcium salts become more soluble.
4. The presence of ascorbic acid and certain amino acids facilitate calcium absorption by increasing the solubility of calcium salts.
5. Lactose is known to enhance calcium absorption. Therefore, milk is the best source of calcium.