<unk>  is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells.<unk>  is composed of<unk>  cells suspended in<unk>  plasma. Plasma, which constitutes 55% of<unk>  fluid, is mostly water (92% by volume), and contains proteins, glucose, mineral ions, hormones, carbon dioxide (plasma being the main medium for excretory product transportation), and<unk>  cells themselves. Albumin is the main protein in plasma, and it functions to regulate the colloidal osmotic pressure of<unk> . The<unk>  cells are mainly red<unk>  cells (also called RBCs or erythrocytes), white<unk>  cells (also called WBCs or leukocytes) and platelets (also called thrombocytes). The most abundant cells in vertebrate<unk>  are red<unk>  cells. These contain hemoglobin, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas and greatly increasing its solubility in<unk> . In contrast, carbon dioxide is mostly transported extracellularly as bicarbonate ion transported in plasma. Vertebrate<unk>  is bright red when its hemoglobin is oxygenated and dark red when it is deoxygenated. Some animals, such as crustaceans and mollusks, use hemocyanin to carry oxygen, instead of hemoglobin. Insects and some mollusks use a fluid called hemolymph instead of<unk> , the difference being that hemolymph is not contained in a closed circulatory system. In most insects, this<unk> " does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough for their tracheal system to suffice for supplying oxygen. Jawed vertebrates have an adaptive immune system, based largely on white<unk>  cells. White<unk>  cells help to resist infections and parasites. Platelets are important in the clotting of<unk> . Arthropods, using hemolymph, have hemocytes as part of their immune system.<unk>  is circulated around the body through<unk>  vessels by the pumping action of the heart. In animals with lungs, arterial<unk>  carries oxygen from inhaled air to the tissues of the body, and venous<unk>  carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled. Medical terms related to<unk>  often begin with hemo- or hemato- (also spelled haemo- and haemato-) from the Greek word (haima) for<unk> ". In terms of anatomy and histology,<unk>  is considered a specialized form of connective tissue, given its origin in the bones and the presence of potential molecular fibers in the form of fibrinogen.
Blood
Serum 
Body fluid
Venous blood
Urine
Cord blood
Feces
Arterial blood