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.
Most marine life is found on the reef slope. Fringing reefs are the most common type of coral reef. A barrier reef is separated from the shore by a lagoon. The reef forms a barrier between the coast and the open ocean or sea. Some barrier reefs consist of chains of smaller reefs separated by narrow waterways.