Blood bone marrow in a process called hematopoiesis, which includes erythropoiesis, the production of red blood cells; and myelopoiesis, the production of white blood cells and platelets. During childhood, almost every human bone produces red blood cells; as adults, red blood cell production is limited to the larger bones: the bodies of the vertebrae, the breastbone (sternum), the ribcage, the pelvic bones, and the bones of the upper arms and legs. In addition, during childhood, the thymus gland, found in the mediastinum, is an important source of T lymphocytes. The proteinaceous component of blood (including clotting proteins) is produced predominantly by
Fatty streak developed countries have fatty streaks, with coronary fatty streaks beginning in adolescence. Fatty streak A fatty streak is the first grossly visible (visible to the naked eye) lesion in the development of atherosclerosis. It appears as an irregular yellow-white discoloration on the luminal surface of an artery. It consists of aggregates of foam cells, which are lipoprotein-loaded macrophages, located in the intima, the innermost layer of the artery, beneath the endothelial cells that layer the lumina through which blood flows. Fatty streaks may also include T cells, aggregated platelets, and smooth muscle cells. It is the precursor lesion of atheromas