Where are blood cells mostly manufactured?

Answer 1

All blood cells development are initiated in the bone marrow but might complete its development in other areas of the body. All of red blood cell development takes place in the bone marrow, but a critical growth factor EPO (Erythropoietin) is made in the kidney and sent to the bone marrow.

White blood cells come in a bunch of different types, T cells, B cells, and Macrophages. T cell development begins in the bone marrow, but its maturation is completed in the thymus gland (think T cells, T-hymus). B cell development begins in the bone marrow as well but then moves to a other parts of the body to complete its maturation, such as the spleen, lymph nodes, or gut lymphatic nodules. Macrophages begin their development in the bone marrow as well and then can go to a variety of places to become tissue specific macrophages. The lungs, brain, liver, and skin all have separate tissue specific macrophages.

Platelets are the last type of blood cell or blood element (does not contain a nucleus, as does RBC). Platelets are formed from megakaryocytes, which are large cells in the bone marrow. Megakaryocytes then bud off part of its long processes, which become circulating platelets.

I hope this answers your question on the location of blood cells manufacturing. As you can see majority of the process occurs in the bone marrow.