Red blood cells, also known as erythrocytes, are unique compared to other cells in that they lack a nucleus. During their development, red blood cells undergo a process called enucleation, where they expel their nucleus to maximize space for hemoglobin, the protein responsible for transporting oxygen. This adaptation allows red blood cells to carry more oxygen and improves their flexibility to navigate through blood vessels.
Without a nucleus, red blood cells cannot divide or repair themselves, which is why they have a limited lifespan of about 120 days. After this period, they are typically removed by the spleen and liver, and new red blood cells are produced in the bone marrow. The absence of a nucleus is a defining characteristic that plays a crucial role in their primary function — efficient oxygen transport throughout the body.