Blood Disorders

The blood is a type of body fluid that delivers necessary substances such as nutrients and oxygen and excludes metabolic waste products. In vertebrates including humans, blood is composed of blood cells suspended in plasma. Plasma, which constitutes 55% of blood fluid, is mostly water and contains proteins, glucose, mineral ions, hormones, carbon dioxide, and blood cells themselves. The blood cells which are mainly derived from hematopoietic stem cells in bone marrow are composed of red blood cells (RBCs/erythrocytes), white blood cells (WBCs/leukocytes), and platelets. RBCs are the most abundant cells among them which contain hemoglobin, an iron-containing protein, to facilitate oxygen transport. Vertebrate blood is bright red when its hemoglobin is oxygenated and dark red when it is deoxygenated. WBCs have nuclei, which distinguishes them from RBCs and platelets. WBCs can be divided into neutrophils, eosinophils, basophils, lymphocytes, and monocytes according to their physical and functional characteristics. Platelets are derived from the megakaryocytes of the bone marrow, and then enter the circulation. Circulating inactivated platelets are biconvex discoid structures, whereas activated platelets have cell membrane projections covering their surfaces. Platelets are only found in mammal.