Why red blood cells do not contain vessels?

Red blood cells, unlike most other cells in the body, do not contain a nucleus or any other organelles, including blood vessels. This allows them to have a greater surface area for oxygen exchange and more room to carry hemoglobin, the molecule responsible for transporting oxygen in the bloodstream. Without a nucleus or organelles, red blood cells also lack the machinery needed to repair themselves, so they have a relatively short lifespan of about 120 days, after which they are removed and replaced by new red blood cells produced in the bone marrow.