Orthopedic surgeons receive 5 or more extra years of training after school. 1  They specialize in the care of disorders of the bones, muscles, tendons, and ligaments. They are trained to manage joint problems with both operative and non-operative techniques.
What the Immune System Does. The immune (pronounced: ih-MYOON) system, which is made up of special cells, proteins, tissues, and organs, defends people against germs and microorganisms every day. In most cases, the immune system does a great job of keeping people healthy and preventing infections.
Living organisms are composed primarily of carbon, oxygen, and hydrogen. Other elements in living matter include calcium, nitrogen, phosphorus, potassium, and trace amounts of other elements. Water is made up of hydrogen and oxygen. The oceans also contain salt, made up of sodium and chlorine. The atmosphere is mostly made up of the element nitrogen, existing in diatomic form (N2). It also includes oxygen, carbon (in carbon dioxide) and a small amount of other elements.