Red blood cells, also known as erythrocytes, are the most common cells in human blood and play an essential role in the transportation of oxygen in the body. These small, disc-shaped cells contain the red blood pigment haemoglobin, which is responsible for binding and transporting oxygen from the lungs to the tissues. Red blood cells are produced in the bone marrow and have a lifespan of around 120 days. After that, they are broken down in the spleen and liver and their components are recycled. A healthy human body produces millions of new red blood cells every day to meet oxygen transportation needs. A normal healthy adult has about 20-30 trillion red blood cells in the bloodstream, which are constantly kept in balance to ensure optimal oxygen supply to organs and tissues. A lack of red blood cells can lead to anemia, while an excessive number of red blood cells can lead to an overproduction of blood cells. Overall, red blood cells are a vital component of the blood, supplying the body with oxygen and thus enabling the organism to survive and function normally.