Structure:
Parathormone is a protein hormone secreted by the chief cells of the gland.
Function:
Parathormone is the most important regulator of blood Ca++; falling levels
promote secretion and elevated levels decrease secretion. Parathormone
acts on the bones to promote digestion of
the matrix for releasing calcium. In the kidneys,
PTH signals increased absorption of calcium from the blood, and in the
intestine, it signals for increased
absorption for dietary calcium. For this last capability, PTH increases
the kidney's metabolism of Vitamin D from the intestine, or that produced
by the skin, to calcitriol, a
Vitamin D3 product. With D3, the intestine is able to absorb more calcium.
