The correct option is 120 days.
Explanation
Red Blood Cells (RBCs), or erythrocytes, are the formed elements of blood responsible for the transport of respiratory gases (oxygen and carbon dioxide). In mammals, mature RBCs are enucleated (lack a nucleus) to accommodate maximum hemoglobin.
Detailed Analysis:
- Lifespan: The average lifespan of a human red blood cell is approximately 120 days.
- Production and Destruction: RBCs are formed in the red bone marrow through a process known as erythropoiesis. After circulating for about four months, their cell membranes become fragile.
- Graveyard of RBCs: Old and damaged RBCs are removed from the circulation and destroyed by macrophages, primarily in the spleen (often called the "graveyard of RBCs") and the liver. The iron component of hemoglobin is conserved and recycled.
Key Takeaway: Human erythrocytes circulate for approximately 120 days before being destroyed in the spleen.