There are approximately 25 trillion red blood cells in the five liters of blood in the human body, which could carry up to 25 sextillion (25 × 1021) molecules of oxygen in the body at any time. Each hemoglobin molecule binds four oxygen molecules so that each red blood cell carries one billion molecules of oxygen. Hemoglobin is packed into red blood cells at a rate of about 250 million molecules of hemoglobin per cell. The principal job of this protein is to carry oxygen, but it also transports carbon dioxide as well. The red coloring of blood comes from the iron-containing protein hemoglobin. In mammals, red blood cells are small biconcave cells that at maturity do not contain a nucleus or mitochondria and are only 7–8 µm in size. Red blood cells, or erythrocytes (erythro- = “red” -cyte = “cell”), are specialized cells that circulate through the body delivering oxygen to cells they are formed from stem cells in the bone marrow. Platelets form clots that prevent blood loss after injury. White blood cells-including neutrophils, monocytes, lymphocytes, eosinophils, and basophils-are involved in the immune response. Red blood cells deliver oxygen to the cells and remove carbon dioxide. The cells and cellular components of human blood are shown. Each of these blood components plays specific roles in maintaining the health of the body. The three main types of cells in human blood are red blood cells, also called erythrocytes, white blood cells, or leukocytes, and platelets, or thrombocytes. Blood plays a protective role by transporting clotting factors and platelets to prevent blood loss and transporting disease-fighting agents to sites of infection.īlood is actually a term used to describe the liquid that moves through the vessels and includes plasma (the liquid portion, which contains water, proteins, salts, lipids, and glucose) and the different types of cells found in the plasma. Blood supports growth by distributing nutrients and hormones, and by removing waste. Blood helps maintain the body’s systems in working order by stabilizing pH, temperature, proper amounts of water, salts and nutrients, and by eliminating excess heat. What exactly is blood, and what does it do? Blood, like the human blood illustrated in Figure 1 is important for regulation of the body’s systems and homeostasis. Most of us have suffered a cut or a scraped knee and have seen our own blood. 2.3 Components of the Blood The Role of Blood in the Body
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