Red bone marrow is the bone marrow of the human body with hematopoietic function. It is called red bone marrow because it contains a large number of red blood cells and is red in color. In infants and young children, most of the body’s bone marrow is red, indicating that infants and young children have a strong hematopoietic function. As they grow older, the red marrow becomes less and less, and some areas become fatty, giving rise to yellow marrow red. Red bone marrow is mainly seen in the ends of long bones, flat bones or irregular bones; for the elderly, due to the decline of hematopoietic function, the parts of red bone marrow will become less and less, and yellow bone marrow will become more and more, indicating that the hematopoietic function of bone marrow is gradually declining. However, when there is acute blood loss, such as hemorrhoid bleeding or gastrointestinal bleeding, some yellow bone marrow will become red bone marrow and perform hematopoietic function, so human bone marrow has a strong compensatory function.