Blood formation in the human body is truly a remarkable process. Blood cells do not form in the bloodstream itself, but in certain areas of the body where bone marrow is present. Where bone marrow is and blood formation takes place depends on whether you are a child or an adult. The first place of blood formation is in the embryo's yolk sac. This is a membranous sac attached to the embryo in-utero where it functions in embryo nutrition. As the embryo grows and ages, the liver takes up some of the responsibility of blood cell formation, usually around twelve to sixteen weeks of gestation. Eventually just before birth, the process of blood formation is taken over by the marrow, the same marrow used to replace cells for adults. During infancy and childhood all bone marrow is red bone marrow, but as one gets older, less blood cell production is needed and some of the red marrow turns to fat.
Red bone marrow is found in adults in flat and irregular bones, such as those in our ribs, scalp and pelvis. In addition to this, lymphatic tissue, tissue found in the spleen, thymus and lymph nodes contribute to the production of our blood cells. All of our red blood cells and most of our white, as well as our necessary blood clotting platelets are produced by the bone marrow. Special white blood cells known as lymphocytes are produced by the spleen, thymus and lymph nodes, while monocytes, another type of white blood cell are produced both by these organs, but also by the liver. Platelets are produced from giant megakaryocytes, in the bone marrow. All blood cells originate from precursors in the bone marrow, known as stem cells.
Normally the bone marrow produces about one pint of blood from the bone marrow weekly, with about one percent of what's needed produced per day. This percentage helps to keep the balance between what is needed to be produced and what is lost daily in aged cells. Red marrow is one of the largest and most active organs of the human body, about the size of the liver in overall but distributed throughout the body.
The human diet is very important in the maintenance of blood cell production, in particular for red blood cell production. With the many quirky diets around, some people do not get the sufficient nutrition needed for red blood cell production and maintenance. Protein, Vitamins B6 and B 12, Folate, Vitamin C, and Iron are all essential nutrients required in the upkeep of red blood cells. Certain disease conditions can trigger the production of new cells by stimulating the hormone Erythropoietin, which in turn stimulates the production of new cells. Erhthropoietin is secreted by the kidneys in response to anoxia, a decrease in oxygen (the red blood cells carry oxygen throughout the body), which triggers the production of the newly needed cells.
The process of blood formation in the body is rather complex and its importance is obvious. Without this complex production and maintenance system, we would not exist.