Calcium concentration in the blood must be maintained within tight limits. The parathyroid gland and the active form of vitamin D, calcitriol, work together to maintain these calcium levels. When the parathyroid gland senses that blood calcium is low, it releases parathyroid hormone, as diagrammed in Figure 9-3. The parathyroid hormone triggers the kidneys to release calcitriol and reabsorb more calcium to boost blood calcium levels. Kidney resorption is the quickest way to raise blood calcium levels. If more blood calcium is needed, the kidneys release more calcitriol, which causes increased absorption of calcium from the intestines.
If still more calcium is needed, calcitriol forces bones to give up some of their
Figure 9-3 Calcium regulation.
calcium into the bloodstream. Calcitriol removes calcium from bones by activating the osteoclast cells in the bones.
Calcium’s Roles in the Body
Calcium is needed by bones and teeth for strength.
Calcium enables muscle contraction.
Calcium helps the blood vessels relax and constrict.
Calcium is needed for nerve impulse transmission.
Calcium is used in the secretion of hormones such as insulin.
Calcium is needed by a number of proteins and enzymes.
The binding of calcium ions is required for blood clotting.
Adequate calcium may be helpful in reducing high blood pressure.
Calcium may help prevent intestinal cancer.
If still more calcium is needed, calcitriol forces bones to give up some of their
Figure 9-3 Calcium regulation.
calcium into the bloodstream. Calcitriol removes calcium from bones by activating the osteoclast cells in the bones.
Calcium’s Roles in the Body
Calcium is needed by bones and teeth for strength.
Calcium enables muscle contraction.
Calcium helps the blood vessels relax and constrict.
Calcium is needed for nerve impulse transmission.
Calcium is used in the secretion of hormones such as insulin.
Calcium is needed by a number of proteins and enzymes.
The binding of calcium ions is required for blood clotting.
Adequate calcium may be helpful in reducing high blood pressure.
Calcium may help prevent intestinal cancer.
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