Problem description:
Do red blood cells have nuclei? Are they totipotent?
Analysis:
Mammalian red blood cells have no nucleus and lose totipotency. Other animals also have it.
Hematopoietic stem cells are also called pluripotent stem cells. It is a group of primitive hematopoietic cells existing in hematopoietic tissue. It can also be said that it is the primitive cell of all blood cells (mostly immune cells). Hematopoietic stem cells are directionally differentiated and proliferated into different blood cell lines and further produce blood cells. Human hematopoietic stem cells first appeared in the yolk sac of the second to third week of embryonic age, and moved to the liver and spleen in the early embryo (second to third month), and moved from the liver and spleen to the bone marrow in the fifth month. From the end of embryo to birth, bone marrow becomes the main source of hematopoietic stem cells. It has multipotentiality, that is, it has two functions: self-replication and differentiation. In embryos and rapidly regenerated bone marrow, hematopoietic stem cells are mostly in the proliferation cycle; In normal bone marrow, most of them are at rest stage (G0 stage). When the body needs it, one part differentiates and matures, and the other part differentiates and proliferates, so as to keep the number of hematopoietic stem cells relatively stable. Hematopoietic stem cells further differentiate into directional stem cells of different blood cell lines. Directed stem cells are mostly in the proliferation cycle, and further differentiate into blood cell lines of various systems, such as red blood cell line, granulocyte line, mononuclear-phagocytic cell line, megakaryocyte line, lymphocyte line and so on. Lymphocytes differentiated from hematopoietic stem cells have two developmental pathways. One is that they differentiate and mature into thymus-dependent lymphocytes, that is, T cells, under the action of thymus and the catalysis of thymosin. The other is not affected by thymus, but by bursa of fabricius (birds) or cystic organs (mammals), and differentiates into cyst-dependent lymphocytes or bone marrow-dependent lymphocytes, that is, B cells. T cells and B cells induce cellular immunity and humoral immunity respectively. If hematopoietic stem cells are lacking in the body, it will cause serious immune deficiency.
Generally speaking, hematopoietic stem cells → red blood cells → red blood cells.