Adult stem cells are found in tissues that are already developed.
Adult stem cells can be isolated from tissues including brain. Mostly it is isolated from bone marrow, which is located in the center of some of the bones.
There are different stem cells found in bone marrow.
Hematopoietic stem cells forms the blood
Endothelial stem cells forms the vascular system (arteries and veins)
Mesenchymal stem cells form the bone, cartilage, muscle, fat and fibroblasts.
Stem cell plasticity theory suggests that the adult stem cells can form different stem cell types. Cells from the bone marrow can form blood forming cells and also can regenerate damaged livers, kidneys, hearts, lungs and other organs.
Adult stem cells exist in certain mature tissues and supply the tissue with replacement cells throughout life.
Compared to embryonic stem cells, which can make replacement cells for any tissue, adult stem cells are normally dedicated to making the cells for one particular tissue.