Definition. The normal concentration of sodium in the blood plasma is 136-145 mM. Hyponatremia occurs when sodium falls below 130 mM. Plasma sodium levels of 125 mM or less are dangerous and can result in seizures and coma. Description. Sodium is an atom, or ion, that carries a single positive charge.
reef1. 1  a ridge of rocks or sand, often of coral debris, at or near the surface of the water. 2  Mining. a lode or vein.
1 Coral reefs are large marine structures that generally form in shallow waters. 2  Coral reefs can be hundreds or even thousands of miles long (see lower photo right). 3  Coral reefs are built by innumerable tiny, wormlike animals living in colonies. 4  These animals are known as polyps (pronunciation: PAWL-ips).