Which type of blood cell carries oxygen around the body?

Red blood cells carry oxygen around the body. They do this using hemoglobin, an iron-containing protein that binds oxygen in the lungs and releases it to tissues as blood moves through tiny capillaries.

Red blood cells, also called erythrocytes, are made in the bone marrow. Mature human red blood cells lack a nucleus, leaving more internal space for hemoglobin and helping the cells bend as they pass through narrow vessels. Their flexible, disc-like shape also gives them a large surface area for gas exchange.

A typical red blood cell circulates for about 120 days before being removed mainly by the spleen and liver. The body continually replaces them, and the hormone erythropoietin helps stimulate production when oxygen levels are low.

A common mix-up is assuming that plasma carries most oxygen or that white blood cells perform this job. Plasma transports some dissolved oxygen, but hemoglobin inside red blood cells carries the overwhelming majority. Red blood cells also help transport carbon dioxide back toward the lungs.