Red blood cells are blood components that transport oxygen throughout the body. Learn about blood orange inside structure, function, and related disorders.

Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in “Kaplan AP Biology” and “The Internet for Cellular and Molecular Biologists. Red blood cells, also called erythrocytes, are the most abundant cell type in the blood. Other major blood components include plasma, white blood cells, and platelets.

A red blood cell has what is known as a biconcave shape. Both sides of the cell’s surface curve inward like the interior of a sphere. This shape aids in a red blood cell’s ability to maneuver through tiny blood vessels to deliver oxygen to organs and tissues. Red blood cells are also important in determining human blood type. Blood type is determined by the presence or absence of certain identifiers on the surface of red blood cells.

Erythrocytes have a large surface for gas exchange and high elasticity to navigate through capillary vessels. Red blood cells have a unique structure. Their flexible disc shape helps to increase the surface area-to-volume ratio of these extremely small cells. This enables oxygen and carbon dioxide to diffuse across the red blood cell’s plasma membrane more readily. Unlike other cells of the body, mature red blood cells do not contain a nucleus, mitochondria, or ribosomes. The absence of these cell structures leaves room for the hundreds of millions of hemoglobin molecules found in red blood cells.

A mutation in the hemoglobin gene can result in the development of sickle-shaped cells and lead to sickle cell disorder. Bone marrow is where blood cell production takes place. Red blood cells are derived from stem cells in red bone marrow. New red blood cell production, also called erythropoiesis, is triggered by low levels of oxygen in the blood. Low oxygen levels can occur for various reasons including blood loss, presence in high altitude, exercise, bone marrow damage, and low hemoglobin levels. When the kidneys detect low oxygen levels, they produce and release a hormone called erythropoietin.

Erythropoietin stimulates the production of red blood cells by red bone marrow. As more red blood cells enter blood circulation, oxygen levels in the blood and tissues increase. When the kidneys sense the increase in oxygen levels in the blood, they slow the release of erythropoietin. Red blood cells circulate on average for about four months.