Final answer:
When calcium intake is inadequate, the body maintains vital functions by pulling calcium from the bones. This process is part of calcium homeostasis, crucial for health, and regulated by vitamin D and hormones like PTH and calcitonin.
Step-by-step explanation:
If calcium intake is inadequate, calcium is pulled from the bones to support critical bodily functions such as blood coagulation, muscle contraction, nerve functioning, and maintaining bone strength. This process is part of calcium homeostasis, which is the maintenance of a steady level of calcium in the blood. The normal blood calcium level is about 10 mg/dL. When dietary calcium is lacking, the body will compensate by releasing calcium from the skeleton, which can weaken bones over time, potentially leading to conditions like osteoporosis.
Calcium homeostasis is regulated by hormones such as parathyroid hormone (PTH), vitamin D, and calcitonin, with coordination among the skeletal, endocrine, digestive, and urinary systems. Without sufficient vitamin D, calcium absorption through the intestines is compromised, leading to a higher demand for calcium from bone reserves.