Final answer:
The smaller size of older spherocytes is mainly due to the loss of membrane blebs, not decreased hemoglobin production or changes in cell flexibility. This process is a result of the natural aging of the cells, where parts of the cell membrane are progressively lost.
Step-by-step explanation:
The smaller size of older spherocytes is attributed to the loss of membrane blebs over time. As spherocytes age, they lose parts of their cell membrane, which leads to a decrease in cell size. This natural attrition process over the lifespan of a spherocyte results in progressively smaller cells.
Unlike conditions such as sickle cell anemia, where abnormal hemoglobin called hemoglobin S causes erythrocytes to assume a sickle shape and obstruct capillaries, the size reduction in spherocytes is due to physical membrane loss rather than changes in hemoglobin production or cell flexibility. Erythrocytes are normally biconcave disks, providing a high surface area to volume ratio which is critical for gas exchange and enables them to traverse the narrow capillaries without issue.
Structural proteins like spectrin provide the necessary flexibility for these maneuvers. The loss of cell membrane components in spherocytes, however, does not affect hemoglobin production or the surface area to volume ratio in a way that could lead to smaller erythrocyte size.