All red blood cells (erythrocytes) in a healthy adult originate in the:

• A. Spleen
• B. Red bone marrow
• C. Thymus
• D. Liver

Answer: (B)

Verified step by step guidance

1. Understand the function of red blood cells (erythrocytes): they are responsible for carrying oxygen throughout the body using hemoglobin.
2. Recall the process of hematopoiesis, which is the formation of blood cells, including red blood cells.
3. Identify the primary site of hematopoiesis in a healthy adult, which is the red bone marrow found within certain bones.
4. Recognize that other organs like the spleen, thymus, and liver have different roles: the spleen filters blood and recycles old red blood cells, the thymus is involved in T-cell maturation, and the liver has various metabolic functions but does not produce red blood cells in adults.
5. Conclude that all red blood cells in a healthy adult originate from the red bone marrow, making it the correct answer.