Functions of calcium for skeletal system and teeth:
- Stability of the skeletal system – in addition to the collagen matrix, calcium salts are the stabilizing factor of the skeletal system; calcium, together with inorganic phosphate in the form of hydroxyapatite, exerts support functions in bones and teeth and gives strength to the bone to maintain the body shape
- Storage function – calcium phosphate serves as a reservoir for the skeletal system to maintain a constant serum calcium concentration of 2.5 mmol/L (10 mg/dL) (range 2.25-2.75 mmol/L); in the event of inadequate dietary intake or severe renal losses of calcium and phosphate, the stored minerals are released from bone and mobilized into the extracellular space – to the detriment of bone stability – to prevent a drop in serum calcium concentration
Dissolved as well as free calcium is involved in the regulation of numerous intracellular and extracellular processes. In this context, extracellular calcium ensures the constant replenishment of calcium-dependent intracellular processes. Calcium enters cells by diffusion, by activation of slow calcium channels, and via a sodium-calcium exchange carrier, where it is bound by the regulatory protein calmodulin. As a calcium-calmodulin complex, the mineral is able to trigger cell-specific responses. The main focus is on the activation of kinases that phosphorylate one or more proteins or enzymes. The enzymes activated by kinases are in turn essential for important cellular metabolic processes. Kinases can also be activated indirectly by calcium. Via calcium-sensitive receptors on the cell surface of various organs, calcium can influence the stability or activity of numerous enzymes.
Calcium is a component of the following intracellular processes (free intracellular and cytosolic calcium, respectively):
- Muscle contraction-increasing the intracellular free calcium concentration from 10-7 to 10-6 to 10-5 mol/l results in the abolition of inhibition of actin-myosin binding by binding to troponin, leading to contraction of smooth and striated muscle cells; as calcium is rapidly removed from the cell by a calcium ATPase and a secondarily active sodium-calcium exchange carrier, the rapid switch between contraction and relaxation of muscle fibers occurs.
- Release of neurotransmitters, such as the amino acids glutamate, gamma-aminobutyric acid, and aspartate, and the monoamines norepinephrine, dopamine, serotonin, and octopamine.
- Hormone secretion
- Glandular secretion
- Ensuring cellular metabolism
- Cell differentiation and proliferation
- Expression of genes
- Visual process
- Glycogen metabolism
Calcium is a component of the following extracellular processes (free extracellular calcium):
- Cell-cell adhesion
- Cell membrane stabilization
- Ensuring gap junctions – channel-like connections between neighboring cells composed of a protein called connexin; they are essential for the exchange of low-molecular-weight signaling, nutrients, and vital substances and are essential for the regulation of growth and developmental processes
- Sealing of the epithelia (tissue structures) – in the intestine and vessels.
- Activation of the blood clotting cascade
- Nerve and muscle excitability