Final answer:
Hematopoietic stem cells found in the bone marrow differentiate through hematopoiesis to produce all formed elements of the blood. These stem cells are part of a hierarchal system originating from embryonic hemangioblasts. Myeloid stem cells, in particular, give rise to erythrocytes, platelets, monocytes, and certain leukocytes.
Step-by-step explanation:
The cells that give rise to all the formed elements of the blood derived from mesenchyme are known as hematopoietic stem cells (HSCs). These stem cells originate in the bone marrow and undergo a process known as hematopoiesis. Hematopoietic stem cells differentiate to give rise to two distinct lineages: myeloid and lymphoid stem cells. The myeloid stem cells are responsible for the production of most formed elements, including erythrocytes, megakaryocytes (which produce platelets), and a myeloblast lineage that gives rise to monocytes and three forms of granular leukocytes: neutrophils, eosinophils, and basophils. The lymphoid stem cells, on the other hand, give rise to various types of lymphocytes, which are part of the body's immune system.
These stem cells can be traced back to hemangioblasts, embryonic stem cells that appear in the mesoderm and give rise to both angioblasts and pluripotent stem cells. These pluripotent stem cells, found in regions known as blood islands, later differentiate into the various formed elements of blood during fetal development. Furthermore, in cases where there is bone marrow failure due to diseases like bone cancer, the liver and spleen can continue to generate formed elements through a process referred to as extramedullary hemopoiesis.