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When bone marrow develops, it eventually assumes the task of forming most of the blood cells for the entire organism. [3] However, maturation, activation, and some proliferation of lymphoid cells occurs in the spleen, thymus, and lymph nodes. In children, haematopoiesis occurs in the marrow of the long bones such as the femur and tibia.
This process indicates that, subsequent to bone marrow transplantation, symmetrical cell divisions into two daughter hematopoietic stem cells must occur. Stem cell self-renewal is thought to occur in the stem cell niche in the bone marrow, and it is reasonable to assume that key signals present in this niche will be important in self-renewal. [2]
In postnatal birds and mammals (including humans), this usually occurs within the red bone marrow. [2] In the early fetus, erythropoiesis takes place in the mesodermal cells of the yolk sac. By the third or fourth month, erythropoiesis moves to the liver. [3] After seven months, erythropoiesis occurs in the bone marrow.
That bone marrow is a priming site for T-cell responses to blood-borne antigens was first described in 2003. [13] Mature circulating naïve T cells home to bone marrow sinuses after they have passed through arteries and arterioles. [14] They transmigrate sinus endothelium and enter the parenchyma which contains dendritic cells (DCs).
When bone marrow develops, it eventually assumes the task of forming most of the blood cells for the entire organism. [3] However, maturation, activation, and some proliferation of lymphoid cells occurs in the spleen, thymus, and lymph nodes. In children, haematopoiesis occurs in the marrow of the long bones such as the femur and tibia.
The function or significance of mitosis, is the maintenance of the chromosomal set; each formed cell receives chromosomes that are alike in composition and equal in number to the chromosomes of the parent cell. Mitosis occurs in the following circumstances: Development and growth: The number of cells within an organism increases by mitosis.
These cells descend from the primitive reticulum cells, which are found in the stroma of the marrow. There is also an intermediate phase between the myeloblast and these primitive reticulum cells, namely the hemocytoblast. At this time several developing blood cell lines are available, like erythropoiesis and thrombopoiesis.
The number of chondrocyte cells created and their maturation process can be influenced by multiple different genes and proteins. Two proteins, bone morphogenetic protein 4 (BMP-4) and fibroblast growth factor 2 (FGF2) have been seen to influence the amount of differentiation into chondrocytes. [ 4 ]