What is bone marrow?

Bone marrow exists in the bone marrow cavities of long bones (such as humerus and femur) and flat bones (such as ilium). It is a spongy tissue, accounting for about 4%-6% of body weight, and it is the largest hematopoietic organ in human body. Bone marrow is divided into red bone marrow and yellow bone marrow. The bone marrow that can produce blood cells is red and is called red bone marrow. Red bone marrow is mainly distributed in flat bone, irregular bone and cancellous bone with long epiphysis, and its hematopoietic function is active. There are only a few immature blood cells in yellow bone marrow, so it still maintains hematopoietic potential and can be transformed into red bone marrow for hematopoiesis when the body needs it. In fetuses and infants, bone marrow is red bone marrow. Fat tissue has appeared in the bone marrow cavity of long bones since about 5 years old. With the increase of age, fat fills all the bone marrow cavities of long bones (light yellow, called yellow bone marrow), and finally almost only flat bones and long epiphyses have red bone marrow. This change may be due to the fact that adults do not need all bone marrow cavity hematopoiesis, and some bone marrow cavity hematopoiesis is enough to supplement the needed blood cells. When the body is severely ischemic, part of the yellow bone marrow can be transformed into red bone marrow, and the hematopoietic capacity of bone marrow is significantly improved-the highest hematopoietic capacity can reach 9 times that of normal hematopoiesis. In other words, if only110 bone marrow is preserved, normal hematopoietic function can be completed. In this sense, a small number of bone marrow donor people have no effect on the body.