Red blood cells

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Structure

Red blood cell, or to give then their proper name - Erythrocytes, appear to be flattened circular discs with a small inner concave within the structure. However, this can be affected by a rare but well documentated disease known as sickle cell aneamia [1].

Red blood cells are high oxygen affinity haemoglobin containing structres that can take several different forms in humans depending on the phase of life of the human. For example, foetal haemoglobin takes a different form to adult human haemoglobin and has a higher affinity for oxygen than adult haemoglobin due to less oxygen bieng contained by erythrocytes in the placenta so have to bind oxygen with a greater affinity than Hb A.

Erythrocytes are non-covalently bound, tetrameric, iron containing metalloproteins. They consist of four globular globin sub units. An iron (Fe) atom is located at the centre of a porphyrin cyclic structure and is where the affinity for the oxygen is obtained [2].

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

Foetal Haemoglobin (Hb F) - Consists of two alpha sunits and two gamma sub units. These is present in neonates up to the age of around one year [3].

Function

Red Blood Cells, also known as Erythrocytes, are oxygen transporting cells in mammals and other organisms. They travel through different transport links through the body known as vessels. These vessels keep them enclosed from the extracellular environment but allow for the diffusion of gases between erythrocyte and cell for removal of waste gas/metabolites such as carbon dioxide from the cell and 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 to the cell and for waste products to be uptaken or dissolved in the plasma which carries them through 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, which would be very unefficient 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 red blood cells. This process can be obstructed in particular diseases such as cystic fibrosis (CF).

References

  1. http://www.sanquin.nl/Sanquin-eng/sqn_products_Blood.nsf/All/Erythrocytes.html
  2. http://www.ebi.ac.uk/interpro/potm/2005_10/Page1.htm
  3. J. C. White & G. H. Beaven, FOETAL HAEMOGLOBIN (15), Medical School of London.

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