Red blood cells

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Red blood cells, also known as erythrocytes, are the most common type of cell in the blood. There are approximately 5 million red blood cells in one microliter of blood. Whereas in the same volume of blood there are 4000-11,000 leukocytes and 150,000-450,000 platelets. A red blood cell's main function is to transport oxygen from the lungs to cells and carbon dioxide from the cells to the lungs.



Red Blood Cells are flattened circular disks with a small inner bi-concave structure. Mature red blood cells do not have a nucleus, nor do they contain many of the other organelles you would expect to find in a cell, allowing them to pick up and transport more oxygen in the blood. Their ability to carry oxygen efficiently is due to the presence of a protein, called haemoglobin, that can take several different forms in humans. These forms depend on the phases of the life of an organism. For example, fetal haemoglobin takes a different form to adult haemoglobin. It has a higher affinity for oxygen than adult haemoglobin, due to lesser oxygen being present in the Placenta. It is due to the haemoglobin that the cells take on their red colour.

Erythrocytes are non-covalently bound, tetrameric, iron-containing metalloproteins. They consist of four globular globin subunits. An iron (Fe) atom is located at the centre and is responsible for their oxygen affinity[1]. Structural proteins support the plasma membrane of the red blood cell by forming a network comprising of actin filaments and microtubules. This gives the cell its bi-concave structure[2].

Adult Haemoglobin (Hb A) - Consists of two alpha subunits and two beta subunits.

Foetal Haemoglobin (Hb F) - Consists of two alpha subunits and two gamma subunits. These are present in neonates up to the age of one[3].


Erythrocytes are oxygen transporting cells found in mammals and other organisms. They travel through links in the body which are known as blood vessels. These vessels keep the contents enclosed from the extracellular environment. However, they do allow for the diffusion of gases between erythrocyte and cell for the removal of waste gas/metabolites such as carbon dioxide from the cell. Inward diffusion also occurs for transport of oxygen for aerobic respiration in cells. The increasing acidity/decreasing pH in the cells results in a conformational change in the structure of the erythrocytes causing a dissociation from the oxygen and transport into the cell, and for waste products to be uptaken or dissolved in the plasma which carries them through the vascular passageways. This process is known as gaseous exchange. The vascular compartmentation allows oxygen to be transported around even the largest organisms body to every individual cell. This means that organisms don't rely on simple diffusion of oxygen as this would be very inefficient in large organisms due to the large surface area.

Erythrocytes can take two physical forms; oxygenated, which appears red, and deoxygenated, which appears a dark reddish-brown.

The erythrocytes become oxygenated within the lungs where gaseous exchange occurs between the alveoli and the passing erythrocytes. This process can be obstructed in particular diseases such as cystic fibrosis (CF) or Chronic Obstructive Pulmonary Disease (COPD).


Anaemia is an example of a condition where an individual does not have enough red blood cells. It can also manifest itself if there is insufficient haemoglobin within the red blood cells. Individuals who are anaemic will often experience symptoms such as fatigue, headaches, shortness of breath and dizziness. Some may have iron-deficient anaemia where the individual will experience similar symptoms due to the fact that they do not have enough iron in their body[4]. Treatment of anaemia can be simple, such as taking iron tablets daily[5].


  2. Hardin.J, Bertoni.G, Kleinsmith.J.L, Becker's World of the Cell. 8th Ed.San Francisco. 2012
  3. J. C. White and G. H. Beaven, FOETAL HAEMOGLOBIN (15), Medical School of London.
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