Red blood cells, also known as erythrocytes, are specialized cells in the blood responsible for transporting oxygen from the lungs to the body's tissues. They contain a protein called hemoglobin, which binds to oxygen and gives blood its red color. These cells are produced in the bone marrow and have a lifespan of about 120 days. Once red blood cells reach the end of their life cycle, they are removed from circulation by the spleen and liver. The body continuously produces new red blood cells to maintain healthy oxygen levels. A deficiency in red blood cells can lead to conditions like anemia, which can cause fatigue and weakness.