The formed elements: these are blood cells and cell derivatives. All the formed elements are originally derived from a pleuripotential (multiple potential) stem cell known as a hemocytoblast. These cells are derived from mesenchyme cells which give rise to other types of connective tissue as well. Pleuripotential stem cells are also known as colony forming units (CFU) because their presence in marrow and other locations permits the formation of all types of blood cells.