Bone marrow is a spongy substance found in the center of the bones. It manufactures bone marrow stem cells and other substances, which in turn produce blood cells. Each type of blood cell made by the bone marrow has an important job. Red blood cells carry oxygen to tissues in the body. Platelets stop bleeding by helping blood clot. White blood cells fight infections. Red blood cells (RBCs) These are referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek erythros for "red" and kytos for "hollow vessel", translated as "cell" in modern usage, are the most common type of blood cell and the vertebrate's principal means of delivering oxygen to the body tissues via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or in fish, and release it into tissues while squeezing through the body's capillaries. The cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red colour of the cells and the blood. Each human red blood cell contains approximately 270 million of these hemoglobin molecules. The cell membrane is composed of proteins and lipids, and this structure provides properties essential for physiological cell function such as deformability and stability while traversing the circulatory system and specifically the capillary network. In humans, mature red blood cells are flexible and oval biconcave disks. They lack a cell nucleus and most organelles, to accommodate maximum space for hemoglobin; they can be viewed as sacks of hemoglobin, with a plasma membrane as the sack. The cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages. Each circulation takes about 60 seconds. Approximately 84% of the cells in the human body are 20–30 trillion red blood cells. Nearly half of the blood's volume (40% to 45%) is red blood cells. White Blood Cells Three very important types of white blood cells are essential to the proper functioning of the body's immune system, which fights infection: Neutrophils and Macrophages-These white blood cells fight bacterial and fungal infections by "eating" germs. Lymphocytes-These white blood cells fight bacterial, viral and fungal infections. T lymphocytes, also called T cells, attack viruses and other germs. T cells from the donor also can attack the recipient resulting in a reaction called graft versus host disease. T cells from the recipient can reject the donor bone marrow cell resulting in graft failure. B lymphocytes make antibodies which help destroy germs in our body. Another source of bone marrow stem cells is the blood that circulates in the veins and arteries of all normal people. These stem cells are known as peripheral blood stem cells (PBSC). Patients recovering from chemotherapy and healthy people who are treated with certain drugs that stimulate the growth of the bone marrow have relatively large numbers of PBSC in their blood. The PBSC can be collected and used in certain situations as a source of stem cells for transplantation. Submit Your Manuscript at https://www.imedpub.com/submissions/anatomical-science-research.html or mail us to anatomicalsci@scholarlymed.com Regards Jacqueline Managing Editor Journal of Anatomical Science and Research.