Where does blood come from?

Blood in the human body is produced from hematopoietic stem cells in the bone marrow, which generate blood cells such as plasma, platelets, and white blood cells.

Bone marrow is a soft, sponge-like substance typically located in the central part of human skeletal tissue. Hematopoietic stem cells in the bone marrow produce approximately 95% of the body's blood cells, while other blood-forming organs include the spleen and liver. In adults, most bone marrow is found in the bones of the pelvis, chest, and spine, such as the hip bones, ribs, and vertebrae. Human blood cells are formed through stages of proliferation and differentiation from hematopoietic stem cells in the bone marrow, ultimately developing into red blood cells, white blood cells, and platelets.

Human blood consists of various cellular components including plasma, red blood cells, white blood cells, and platelets. Plasma accounts for about 55%, red blood cells about 44%, and the remaining components include white blood cells, platelets, and other substances. Blood not only helps transport oxygen and nutrients for circulation and absorption throughout the body's systems and tissues, but also aids in promoting the metabolism and elimination of waste products within the body.