328 Anatomy & Physiology Essentials Copyright Goodheart-Willcox Co., Inc. Recycling also occurs through hemolysis, or the rupture of RBCs. This occurs when RBCs approach the end of their 120-day life span. Hemolysis can also result from RBC disorders caused by antibodies, infections, or blood transfusion complications. With the exception of the hemoglobin molecules, the RBC membrane breaks down easily. For a hemo- globin molecule to be recycled, it must first be separated into its two parts—globin and heme. The globin protein is further broken down into amino acids that are later used to make new proteins. The heme is broken down into iron and bilirubin, a waste product. The iron is stored in the liver or spleen until the bone marrow needs it to manufacture new RBCs. The bilirubin is excreted by the liver into bile. Most of the bile is transported to the gallbladder, travels through the intestines, and is reabsorbed in the distal ileum. It then is transported to the liver through the portal circulation. Some bile is excreted in the feces. Leukocytes White blood cells (WBCs), or leukocytes, serve as the body’s infection fighters they play an important role in immune response. At any given time, blood and stimulate RBC production. If an excess of RBCs is produced, polycythemia can develop. Polycythemia is discussed later in this chapter. Iron, folic acid, vitamin B12, and protein are needed for RBC production, as well as for red bone marrow. People who are anemic, and potentially those who have an iron-deficient diet, lack enough iron to properly form the heme component of hemoglobin. The result is iron-deficient anemia, which is discussed later in this chapter. Phagocytosis and Hemolysis Red blood cells have the remarkable ability to bend, twist, and turn, allowing them to fit into capillaries half their size. All of these contortions take their toll on the RBC, quickly causing its membrane to become ragged. The ragged membrane, coupled with the lack of a nucleus, seals the fate of the RBC: death by phagocytosis. Phagocytosis is the process by which macrophages in the liver and spleen envelop, digest, and recycle old RBCs and other types of cells. Macrophages are cells that play a major role in immune system function. Chapter 13 discusses macrophages, phagocytes, and phagocytosis in more detail. Increased RBCs Erythropoiesis (increased RBC production) EPO stimulates Red bone marrow Kidney secretes erythropoietin Conditions that cause low oxygen levels in blood C $6=4=01 1A:9 e C &3 onic obstructive lung disease C (8/ eased O2 intake by tissues © Body Scientific International Figure 11.6 The blood works with the endocrine system to release erythropoietin, which stimulates red blood cell production. Ch11.indd 328 5/3/2019 9:44:33 AM