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.
Coral reefs are solid, long-lasting structures. Their solidity is due to the fact that they are formed by the hard parts of the animal skeletons. Their longevity is due to their ability to resist shocks even after the death of organisms (cf. the high-rising primaeval reefs). The interstices are sealed and soldered by sediments and coral secretions.