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: The Great Barrier Reef is a large and vast coral reef: at  2000km long, it is the largest coral reef in the world.   Barrier: The Great Barrier Reef is a barrier reef. A barrier reef  is one which runs parallel to the shore, separated by a channel of  water.  Great: The Great Barrier Reef is a large and vast coral reef: at  2000km long, it is the largest coral reef in the world.   Barrier: The Great Barrier Reef is a barrier reef. A barrier reef  is one which runs parallel to the shore, separated by a channel of  water.