In humans, blood is pumped from the strong left ventricle of the heart through arteries to peripheral tissues and returns to the right atrium of the heart through veins. Fibrin from the coagulation cascade creates a mesh over the platelet plug.īlood is circulated around the body through blood vessels by the pumping action of the heart. 200,000–500,000 thrombocytes: Also called platelets, they take part in blood clotting ( coagulation).The cancer of leukocytes is called leukemia. 4,000–11,000 leukocytes: White blood cells are part of the body's immune system they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents ( pathogens) and foreign substances.The combined surface area of all red blood cells of the human body would be roughly 2,000 times as great as the body's exterior surface. The proportion of blood occupied by red blood cells is referred to as the hematocrit, and is normally about 45%. The red blood cells (together with endothelial vessel cells and other cells) are also marked by glycoproteins that define the different blood types. Mature red blood cells lack a nucleus and organelles in mammals. 4.7 to 6.1 million (male), 4.2 to 5.4 million (female) erythrocytes: Red blood cells contain the blood's hemoglobin and distribute oxygen.In terms of anatomy and histology, blood 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.Ī scanning electron microscope (SEM) image of a normal red blood cell (left), a platelet (middle), and a white blood cell (right) Medical terms related to blood often begin with hemo- or hemato- ( also spelled haemo- and haemato-) from the Greek word αἷμα ( haima) for "blood". In animals with lungs, arterial blood carries oxygen from inhaled air to the tissues of the body, and venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled. Arthropods, using hemolymph, have hemocytes as part of their immune system.īlood is circulated around the body through blood vessels by the pumping action of the heart. Platelets are important in the clotting of blood. White blood cells help to resist infections and parasites. Jawed vertebrates have an adaptive immune system, based largely on white blood cells. In most insects, this "blood" does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough for their tracheal system to suffice for supplying oxygen. Insects and some mollusks use a fluid called hemolymph instead of blood, the difference being that hemolymph is not contained in a closed circulatory system. Some animals, such as crustaceans and mollusks, use hemocyanin to carry oxygen, instead of hemoglobin.
Vertebrate blood is bright red when its hemoglobin is oxygenated and dark red when it is deoxygenated. In contrast, carbon dioxide is mostly transported extracellularly as bicarbonate ion transported in plasma. These contain hemoglobin, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas and greatly increasing its solubility in blood. The most abundant cells in vertebrate blood are red blood cells. The blood cells are mainly red blood cells (also called RBCs or erythrocytes), white blood cells (also called WBCs or leukocytes) and platelets (also called thrombocytes). Albumin is the main protein in plasma, and it functions to regulate the colloidal osmotic pressure of blood. Plasma, which constitutes 55% of blood 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 blood cells themselves.
In vertebrates, it is composed of blood cells suspended in blood plasma. Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells.