The mature erythrocyte looks like a flexible biconcave cell of a discoid shape, 7-8.5 µm in diameter, and thick 7.5 nm.
The membrane is permeable to oxygen, carbodioxide, water, urea, nitrogen, glucose, chloride, HCO3 - and OH- ions. Increasing CO2 in blood facilitates the entrance of chloride ions, which withdraws water provoking the change in the shape of the cell.
Erythrocyte does not have nucleus and mitochondria.
It contains a significant quantity of enzymes. The only source of energy is glucose that is subjected to the process of glycolysis after entering the cell. All biochemical processes in the erythrocyte are poorly regulated, so a disturbance at a certain point quickly leads to cell death. Glucose degradation is achieved 90% by the anaerobic Embden-Meyerhoff pathway and 10% by the pentose-phosphatic cycle.
The aging of the erythrocyte is related to the membrane destruction and irreversible denaturation of enzymes (protein denaturation).
Erythrocytes degradation is a consequence of “aging”, i.e., the loss of enzymes involved in glycolysis.
Decomposition of old erythrocytes follows this scenario;

• fragmentation,
• osmosis,
• erythrophagocytosis,
• cytolysis by complement, and
• hemoglobin denaturation.

In normal conditions aged erythrocytes are mostly ingested and degraded in the cells of histiomonocytic system in the bone marrow, spleen, and liver.