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Red blood cell

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Red blood cells (also known as RBCs, red blood corpuscles or erythrocytes) are cells in the blood which transport oxygen.[1][2] Red blood cells are very large in number; in women, there are 4.8 million red blood cells per microliter of blood. In men, there are 5.4 million red blood cells per microliter of blood.[3] Red blood cells are red because they have haemoglobin in them.


The most important function of red blood cells is the transport of oxygen. The haemoglobin absorbs oxygen in the lungs, travels through blood vessels and brings oxygen to all other cells via the heart. Since the blood cells go through both the lungs (to collect oxygen), through the heart (to be pumped around the rest of the body to give all cells oxygen) and back to the heart to be re-pumped to the lungs (to again collect oxygen), it is said that the blood in your body travels in a double circuit, going through your heart twice before it completes one full of the body.

A fact which makes mammalian red blood cells different to all other cells is that, when they are mature, red blood cells do not have a nucleus. All other vertebrates have red cells with nuclei.

Red blood cells are doughnut-shaped, but without the hole. This shape is called a bi-concave disc. However, hereditary diseases such as sickle-cell disease can cause them to change shapes and stop blood flow in capillaries and veins. Plasma is got from whole blood. To prevent clotting, an anticoagulant (such as citrate) is added to the blood immediately after it is taken.


Mammalian RBCs are unique among vertebrates as they are non-nucleated cells in their mature form. These cells have nuclei during development, but push them out as they mature. This gives more space for haemoglobin. Mammalian RBCs also lose all other cellular organelles such as their mitochondria, Golgi apparatus and endoplasmic reticulum.

As a result of not having mitochondria, the cells use none of the oxygen they carry. Instead they produce the energy carrier ATP. Because of the lack of nuclei and organelles, mature red blood cells do not contain DNA and cannot synthesize any RNA. They cannot divide, and have limited repair capabilities.[4] This also makes sure no virus can target mammalian red blood cells.[5]


  1. Bradfield, Phil; Potter, Steve (2009). Edexcel IGCSE Biology Student Book. Pearson Education. ISBN 9780435966881 .
  2. Liang, Barbara. "General Anatomy & Physiology: Red Blood Cells". Wisc-Online. Retrieved 2011-03-22.
  4. Kabanova S. et al 2009. "Gene expression analysis of human red blood cells". International Journal of Medical Sciences 6 (4): 156–9. PMC 2677714 . PMID 19421340 .
  5. Zimmer, Carl (2007-03-27). "Scientists explore ways to lure viruses to their death". The New York Times. Retrieved 2013-03-26.

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