Red Blood Cells

Hemoglobin is also involved in regulating blood flow and blood pressure via the release of nitric oxide which causes vasodilation that improves blood flow and enhances oxygen delivery.
Red blood cells also contain carbonic anhydrase which catalyzes the conversion of carbon dioxide and water to carbonic acid. This compound transports about 70% oc carbon dioxide in the plasma. It is also a buffer.

Red blood cells live for only about 120 days. Dead cells are removed from the circulation by the spleen and liver.
Breakdown products from the cells are recycled and reused.