Blood is a type of connective tissue with a liquid extra cellular matrix called plasma. Plasma constitutes around 50-60 percent of the blood while the formed elements suspended in the plasma constitute the other 40-50 percent of whole blood. The formed elements consist of platelets, leukocytes or white blood cells, and erythrocytes or red blood cells. 90 percent of plasma is made up of water which acts as a solvent for a wide variety of substances such as dissolved gases, organic nutrients, plasma proteins, inorganic ions, nitrogenous wastes (urea in humans), and hormones. Dissolved gases include oxygen, carbon dioxide, and nitrogen. Organic nutrients include glucose, fats, phospholipids, amino acids, lactic acid, and cholesterol. Plasma proteins such as fibrinogen, the albumins, and the globulins are synthesized in the liver and lymphoid tissues. Plasma proteins help maintain the proper water balance between the blood and the cells of the body's tissues by determining the correct osmotic pressure of the plasma. The plasma proteins also help maintain the proper viscosity of the blood. Maintenance of homeostasis or the equilibrium of inorganic ion concentrations in the plasma is crucial to the normal functioning of the body and is regulated by the kidneys and certain hormones.
Platelets, cell fragments formed by megakaryocytes in red bone marrow, are involved in the clotting of blood. When platelets hit damaged tissue, they release thromboplastin which, in the presence of ions, converts the plasma protein prothrombin into thrombin. Thrombin, then, converts the plasma protein
