<unk> s <unk> s) are the<unk> <unk> s that give rise to other blood<unk> s. This process is called haematopoiesis. In vertebrates, the very first definitive<unk> s arise from the ventral endothelial wall of the embryonic aorta within the (midgestational) aorta-gonad-mesonephros region, through a process known as endothelial-to-hematopoietic transition. In adults, haematopoiesis occurs in the red bone marrow, in the core of most bones. The red bone marrow is derived from the layer of the embryo called the mesoderm. Haematopoiesis is the process by which all mature blood<unk> s are produced. It must balance enormous production needs (the average person produces more than 500 billion blood<unk> s every day) with the need to regulate the number of each blood<unk>  type in the circulation. In vertebrates, the vast majority of hematopoiesis occurs in the bone marrow and is derived from a limited number of<unk> s that are multipotent and capable of extensive self-renewal.<unk> s give rise to different types of blood<unk> s, in lines called myeloid and lymphoid. Myeloid and lymphoid lineages both are involved in dendritic<unk>  formation. Myeloid<unk> s include monocytes, macrophages, neutrophils, basophils, eosinophils, erythrocytes, and megakaryocytes to platelets. Lymphoid<unk> s include T<unk> s, B<unk> s, natural killer<unk> s, and innate lymphoid<unk> s. The definition of<unk>  has developed since<unk> s were first discovered in 1961. The<unk>  tissue contains<unk> s with long-term and short-term regeneration capacities and committed multipotent, oligopotent, and unipotent progenitors.<unk> s constitute 1:10,000 of<unk> s in myeloid tissue.<unk>  transplants are used in the treatment of cancers and other immune system disorders.
Hematopoietic stem cell
Lymphoblast
Stem cell
Progenitor cell
Megakaryocyte–erythroid progenitor cell
Thymocyte
Monocyte
Dendritic cell