Calcium is used by almost every cell in your body. While most of the calcium your body has is stored in the bones and teeth, each cell has its own way of storing and releasing the calcium it needs when it needs it. Adults under the age of 50 should be getting 1,000 mg per day of calcium, while those 50 and over need 1,200 mg per day. Getting enough calcium assures that your cells can function properly.
Calcium is used inside the cardiac cells to help keep your heart in rhythm. Calcium is stored in the extracellular fluid of the cardiac cells. When your cardiac cells contract, resulting in a heart beat, the calcium outside of your cells flows inward helping to depolarize the cells, because calcium is a positively charged ion. When your cardiac cells reach a zero pole, or 0 mV, the cells contract in rhythm and produce a heart beat. This whole process is not achievable without the presence of calcium.
Your muscle cells also contract with the assistance of calcium. The sarcoplasmic reticulum of your muscle cells stores calcium and releases it when stimulated by the nervous system, which is calling on your muscle to contract. Calcium is essential in a muscular contraction because it helps facilitate the binding of actin and myosin, the two myofilaments responsible for contracting the muscle. Inside each muscle fiber, these two myofilaments are next to one another. Myosin must attach to actin to grab hold of and move the muscle fiber. However, a molecule called tropomyosin blocks the binding site during rest. When the muscle is stimulated to move, the calcium releases and attaches to troponin which in turn changes the shape of tropomyosin and exposes the binding site, allowing for a contraction to take place.
Calcium is also useful for non-muscular cells. According to a report published in "Bioessays" in November 1990, non-muscular cells contain calcium within the endoplasmic reticulum. This report states that many calcium storage proteins have been found in the endoplasmic reticulum of cells, including calreticulun. Its proposed that calcium aids cells in intracellular communication.
Your bones store 99 percent of the calcium that is inside your body, according to the National Osteoporosis Foundation. Your body uses your skeletal system as a calcium savings account. Your cells need constant access to calcium, which is available in the blood. Blood calcium is regulated by hormones sensitive to the amount of calcium in your blood. If there is not enough calcium inside the blood, your body may call upon the calcium inside your bones, especially if your dietary calcium is lacking. If your body continuously takes calcium from your bones, you risk having weak bones, a condition known as osteoporosis.