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.
Great Barrier Reef. n. 1. (Placename) a coral reef in the Coral Sea, off the NE coast of Australia, extending for about 2000 km (1250 miles) from the Torres Strait along the coast of Queensland; the largest coral reef in the world.reat Barrier Reef-the largest coral reef in the world; in the Coral Sea off the northeastern coast of Australia.