The level of calcium in the blood determines which of 2 hormones gets released. This causes an increased absorption from the gut and an increase in bone resorption. Decreased HCL, oxalates, phytates, excess magnesium, and malabsorption are all factors which may decrease the absorption of calcium. Calcium ions add hardness to the bone matrix. Calcium aids transport across cell membranes.
Muscles require calcium to function in their contractility.
Without calcium the muscles tend to stay contracted. Calcium also regulates membrane stabilization. In addition, neurotransmitters at synaptic junctions are regulated by calcium. This may have effects on such conditions such as anxiety, insomnia and other stress conditions. Like striated muscle throughout the body, the heart requires calcium for proper contractility.