The hematologic system is made up of the blood, the spleen, bone marrow, and the liver. Hematology is a branch of medicine concerning the study of blood, the blood forming organs, and blood diseases. The hematopoietic system is not fully developed at birth, and the normal hematologic values of newborns and infants differ as compared to older children and adults. The principal component of the hematologic system is the blood. Plasma is a fluid made up of 90% of water, in which blood is suspended. Plasma allows blood cells to travel through vessels, in the water it contains. Plasma is also made up of minerals, nutrients, and electrolytes. Anemia is a condition in which reduced hematocrit or hemoglobin levels lead to diminished oxygen-carrying capacity that does not optimally meet the metabolic demands of the body. Anemia is not a specific disease entity but is a condition caused by various underlying pathologic processes.