Red blood cells (RBCs) have

Mature mammalian red blood cells (RBCs), or erythrocytes, are specialized for oxygen transport. During their maturation process from reticulocytes, they undergo significant structural changes, including the ejection or degradation of internal organelles [1]. In humans and other mammals, mature RBCs lack a nucleus, which provides more space for hemoglobin molecules and increases oxygen-carrying capacity [2]. Additionally, they lack mitochondria, which prevents the cell from consuming the oxygen it transports for its own metabolic respiration. Instead, RBCs generate energy through anaerobic glycolysis in the cytoplasm. Other organelles, such as the endoplasmic reticulum and ribosomes, are also removed during the final stages of maturation to optimize the cell's biconcave shape and flexibility for circulating through narrow capillaries [3]. Therefore, mature RBCs contain no nucleus, no mitochondria, and no endoplasmic reticulum.

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC8959883/
2. [2] https://www.ncbi.nlm.nih.gov/books/NBK2263/
3. [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC8953437/