Chapter 18 - Section 18.2 - Erythrocytes - Before You Go On - Page 684: 11

When a red blood cell (RBC) reaches the end of its lifespan, it undergoes a process called senescence. During this process, the RBC becomes less functional and is eventually removed from circulation by the body's immune and phagocytic systems. Here's what happens to each component of an RBC and its hemoglobin when it dies and disintegrates: 1. **Cell Membrane and Cytoplasm:** - As an RBC ages, its cell membrane becomes less flexible and more rigid due to changes in the lipid composition. - The cytoplasm loses some of its elasticity, making the cell less able to squeeze through small capillaries. - These changes can lead to the RBC becoming trapped in small blood vessels, particularly in the spleen. 2. **Hemoglobin:** - Hemoglobin within the RBC is broken down into its constituent parts: heme and globin. - The iron ion at the center of the heme group is an essential component of hemoglobin that can be recycled. - The heme group is broken down into biliverdin, which is then converted into bilirubin, a waste product. - Bilirubin is transported to the liver, where it is conjugated (chemically modified) and eventually excreted into bile. 3. **Iron Recycling:** - Iron released from the breakdown of hemoglobin can be recycled and used for the synthesis of new hemoglobin or stored in the body's iron reserves. - Iron not immediately needed for hemoglobin synthesis is stored in the liver, spleen, and bone marrow as ferritin and hemosiderin. 4. **Globin:** - The globin protein chains are broken down into amino acids, which can be reused by the body for various processes. 5. **Phagocytosis and Disposal:** - Senescent RBCs are recognized and engulfed by phagocytic cells, primarily macrophages, located mainly in the spleen and liver. - This process, known as phagocytosis, involves the removal of the cell's membrane and the digestion of its components. - The heme groups' iron is extracted and recycled, while the rest of the heme molecule is converted into biliverdin and bilirubin. - The globin protein is broken down into amino acids and can be used for various cellular processes. 6. **Bilirubin Clearance:** - Bilirubin, a product of heme breakdown, is transported to the liver and conjugated to make it water-soluble. - Conjugated bilirubin is then excreted into bile, which is eventually released into the small intestine. - Bilirubin is further metabolized by gut bacteria and can contribute to the color of feces. In summary, when an RBC dies and disintegrates, its components are broken down and recycled. Hemoglobin is dismantled into heme and globin. The iron is reused or stored, while the rest of the heme molecule is converted and eventually excreted. Globin is broken down into amino acids. The process involves phagocytosis by macrophages, which play a critical role in removing senescent RBCs from circulation and ensuring the recycling of their components.

When a red blood cell (RBC) reaches the end of its lifespan, it undergoes a process called senescence. During this process, the RBC becomes less functional and is eventually removed from circulation by the body's immune and phagocytic systems. Here's what happens to each component of an RBC and its hemoglobin when it dies and disintegrates: 1. **Cell Membrane and Cytoplasm:** - As an RBC ages, its cell membrane becomes less flexible and more rigid due to changes in the lipid composition. - The cytoplasm loses some of its elasticity, making the cell less able to squeeze through small capillaries. - These changes can lead to the RBC becoming trapped in small blood vessels, particularly in the spleen. 2. **Hemoglobin:** - Hemoglobin within the RBC is broken down into its constituent parts: heme and globin. - The iron ion at the center of the heme group is an essential component of hemoglobin that can be recycled. - The heme group is broken down into biliverdin, which is then converted into bilirubin, a waste product. - Bilirubin is transported to the liver, where it is conjugated (chemically modified) and eventually excreted into bile. 3. **Iron Recycling:** - Iron released from the breakdown of hemoglobin can be recycled and used for the synthesis of new hemoglobin or stored in the body's iron reserves. - Iron not immediately needed for hemoglobin synthesis is stored in the liver, spleen, and bone marrow as ferritin and hemosiderin. 4. **Globin:** - The globin protein chains are broken down into amino acids, which can be reused by the body for various processes. 5. **Phagocytosis and Disposal:** - Senescent RBCs are recognized and engulfed by phagocytic cells, primarily macrophages, located mainly in the spleen and liver. - This process, known as phagocytosis, involves the removal of the cell's membrane and the digestion of its components. - The heme groups' iron is extracted and recycled, while the rest of the heme molecule is converted into biliverdin and bilirubin. - The globin protein is broken down into amino acids and can be used for various cellular processes. 6. **Bilirubin Clearance:** - Bilirubin, a product of heme breakdown, is transported to the liver and conjugated to make it water-soluble. - Conjugated bilirubin is then excreted into bile, which is eventually released into the small intestine. - Bilirubin is further metabolized by gut bacteria and can contribute to the color of feces. In summary, when an RBC dies and disintegrates, its components are broken down and recycled. Hemoglobin is dismantled into heme and globin. The iron is reused or stored, while the rest of the heme molecule is converted and eventually excreted. Globin is broken down into amino acids. The process involves phagocytosis by macrophages, which play a critical role in removing senescent RBCs from circulation and ensuring the recycling of their components.