Calcium is the most abundant mineral in the human body. It is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust. Calcium is also the fifth most abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium and sulfate.
Sources of calcium:
• Milk
• Egg
• Fish
• Vegetables
• Wheat
• Rice
Normal value:
9-11mg/dl
Factors necessary for Absorption:
1. Calcium absorption increases by the following:
a. Vitamin D
b. Parathyroid hormone
c. Acidity
d. Aminoacids
2. Calcium absorption decreases by the following:
a. Phytic acid in cereals
b. Oxalates in leafy vegetables
c. Malabsorption syndrome
d. High phosphate content
Parathyroid hormone and Calcium:
Parathyroid hormone is secreted by the 4 parathyroid glands that is embedded in the thyroid tissue.
Formation:
• Pre pro PTH- 115 aminoacids
• Pro PTH- 90 aminoacids
• Mature PTH- 84aminoacids
Role of PTH in bones:
PTH causes demineralization or decalcification. Thus increases calcium level in blood.
Role of PTH in kidneys:
There is decreased renal excretion of calcium and increased excretion of phosphate.
Role of PTH in intestines:
PTH activates Vitamin D which indirectly increases calcium absorption from intestines.
Calcitonin and Calcium:
Calcitonin is secreted by the thyroid parafollicular cells. This hormone inhibits bone resorption and thus decreases phosphate level. In the kidneys it excretes phosphate and lowers plasma calcium level.
Regulation of blood calcium level:
When the plasma levels of calcium decreases it activates PTH gland to secrete PTH and thus increases the level in blood.
When the plasma levels of calcium increases it activates Thyroid cells to secrete Calcitonin and thus decreases the level in blood.
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