An element is a pure substance that is made from a single type of atom. Elements are the building blocks for all the rest of the matter in the world. Examples of elements include iron, oxygen, hydrogen, gold, and helium.
Since the initial discovery that the adult brain contains stem cells that generate new neurons, an important question in neurobiology has been whether or not this adult neurogenesis is functionally important.
The most common (and probably the most studied) source for adult stem cells is the bone marrow, which contains two types: hematopoietic (blood forming cells) and mesenchymal stem cells. Of particular interest in orthopaedic research are bone marrow stromal cells.he stem cells may then be separated from other cells in the marrow and grown or expanded in the laboratory. This may take from 7 to 21 days. When stem cells are placed in a specific tissue environment, such as bone, they become activated.