Final answer:
All circulating red blood cells in an adult originate from the red bone marrow, which is the primary site for hematopoiesis postnatally. Red bone marrow also produces lymphocytes, with B cells maturing there and T cells maturing in the thymus.
Step-by-step explanation:
All the circulating red blood cells in an adult originate in the C) red bone marrow. Hematopoiesis, the process by which blood cells are formed, occurs primarily in red bone marrow. Throughout life, red bone marrow is responsible for the production of red blood cells, which are critical for transporting oxygen to tissues throughout the body.
While in embryonic development, other organs such as the spleen, lymph nodes, and liver have roles in hematopoiesis, it is the red bone marrow that takes over this function as the primary site postnatal. Not to be confused with yellow bone marrow, which serves as energy storage, red bone marrow provides the environment for stem cells to develop into red blood cells and other components of the blood.
The lymphocytes, part of the white blood cells, are also produced in the red bone marrow. B cells mature within the red bone marrow, earning their name 'B' for 'bone marrow,' while T cells migrate to the thymus where they mature, thus named 'T' for 'thymus'.