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.
An atoll is a roughly circular (annular) oceanic reef system surrounding a large (and often deep) central lagoon. IndoPacific atolls. In the South Pacific, most atolls occur in mid-ocean. Examples of this reef type are common in French Polynesia, the Caroline and Marshall Islands, Micronesia, and the Cook Islands.