Final answer:
Hematopoiesis is the blood cell formation process that starts in the embryo's yolk sac and progresses to the spleen and liver, before finally occurring predominantly in the red bone marrow. The liver and spleen can compensate for bone marrow dysfunction through extramedullary hemopoiesis. Hematopoietic stem cells in the red bone marrow are essential for producing all blood cells.
Step-by-step explanation:
Hematopoiesis is the process of blood cell formations which occur in various locations at different developmental stages in life. Initially, in the embryo, blood cells are created in the yolk sac. As the embryo develops, this function transfers to the spleen, liver, and eventually to the bone marrow. The red bone marrow is where hematopoiesis predominates, consisting of a loose collection of cells that generate red blood cells, white blood cells, and platelets. In contrast, the yellow bone marrow serves largely as a site of energy storage comprised primarily of fat cells.
In adulthood, the liver and spleen can engage in a backup form of hematopoiesis known as extramedullary hemopoiesis, especially in cases where diseases compromise the function of the bone marrow. It's also important to note that all formed elements of blood arise from hematopoietic stem cells located within the red bone marrow. These stem cells differentiate into various cell types including the myeloid lineage which gives rise to most blood cells, and the lymphoid lineage which develops into B cells, T cells, and NK cells.