Electrolytes are charged minerals such as sodium, potassium, calcium, phosphate and magnesium that are vitally important for the body. Cells maintain an electrical potential; they are negatively charged relative to their surroundings. Signals can cause them to become transiently positive, or less negative, and thereby perform a function ascribed to the particular cell. Calcium plays vital roles in helping cells as well as proteins carry out their functions.
Calcium in the Body
Most of the calcium in the body is found in the bone. In the blood, calcium is found bound to protein and free in the blood fluid. The normal range for total calcium in the blood is about 9-10.5 mg/dL and the range for free calcium is about 4.5-5.6 mg/dL. Calcium is also found stored inside cells in special calcium-containing structures.
Neurotransmitter Release
Neurotransmitters are chemicals released by nerves that signal nearby cells. Calcium plays a vital role in neurotransmitter release. Neurotransmitters are found in spherical, or bag-like structures, called vesicles, near the end of a nerve process. A nerve linked to a voluntary skeletal muscle, such as the biceps, receives a message in the brain to contract. The message is communicated chemically. At the level of the nerve, special channels open to allow a small amount of sodium into the cell. This makes the cell more positive, and causes more sodium channels to open. This wave of sodium influx passes down the length of the nerve. When it reaches the end of the nerve, where the neurotransmitter is stored, it causes special calcium channels to open. This allows calcium to rush into the nerve. Proteins bound to the vesicles respond to the calcium by fusing with the end of the cell and releasing the neurotransmitter, which signals the muscle to contract.
Muscle Cells
The neurotransmitter released from nerves is called acetylcholine. When it binds to proteins on the muscle cells, it causes calcium levels inside the cell to rapidly increase. The calcium binds to special proteins inside the muscle cells that cause the muscle to contract. Once this occurs, the calcium levels are rapidly pumped out of the cell and the muscle is able to relax and repeat the cycle.
Blood Clotting
Free calcium in the blood is ionized, meaning it has an electrical charge. Calcium has a charge of +2. This means it can bind to negatively charged chemicals. When blood needs to clot, such as from damage to a blood vessel that is causing bleeding, negative charges on the blood vessel walls and blood clotting proteins are exposed. Calcium serves as a bridge, linking the negatively charged blood proteins together; this causes a chain of events that causes the blood to clot.
References
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci et al.; 17th Ed 2008
- "Physiology"; Linda S.Costanzo; 4th Ed 2008
- "Molecular Biology of the Cell"; Bruce Alberts et al.; 4th Ed 2002
