Red blood cells

Structure

Red Blood Cells, also known as Erythrocytes, are flattened circular disks with a small inner concave structure. They 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 life of an organism. For example, foetal 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 sub units. An iron (Fe) atom is located at the centre and is responsible for their oxygen affinity .

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 are present in neonates up to the age of one .

Function

Erythrocytes are oxygen transporting cells found in mammals and other organisms. They travel through different transport links through the body 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 red blood cells. This process can be obstructed in particular diseases such as cystic fibrosis (CF).

Disease

Anaemia is a 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 the do not have enough iron in their body.