Final answer:
B cells are maintained by replacement from the bone marrow, while T cells are maintained by self-renewal. Blood cells differentiate from hematopoietic stem cells in the bone marrow.
Step-by-step explanation:
In contrast to B cells, whose numbers are maintained by replacement from the bone marrow, T cells are maintained by a self-renewal process. Hematopoietic stem cells in the bone marrow differentiate into various blood cells, including B cells, which mature in the bone marrow, and T cell progenitors, which migrate to the thymus for maturation. The self-renewing hematopoietic stem cells follow a hierarchy, beginning from totipotent stem cells and narrowing down to specialized cells such as hematopoietic stem cells, which are the source of all formed elements in the blood.