Your red blood cells

Your red blood cells are the some of the most important transporters in your body.  They bring oxygen to all the cells in your body and take away the carbon dioxide waste products.  But how do they do this? 

When you breathe in, the oxygen from the air is passed from your alveoli, the tiny air sacs in your lungs that look like bunches of grapes, to your red blood cells.  The alveoli are covered in capillaries, tiny, tiny and very thin blood vessels.  Your red blood cells pass through your capillaries one red blood cell at a time.  This allows the oxygen in your alveoli to pass through the wall of the very thin capillary and into the red blood cell.  At the same time, any carbon dioxide waste product that the red blood cell is carrying passes through the wall of the capillary and into your alveoli where it is just removed the next time you breathe out.  There are millions of red blood cells in every drop of your blood, so there is always lots of oxygen and carbon dioxide being exchanged.  It’s simple, and very clever!      

Your red blood cells have a chemical called haemoglobin that actually carries the oxygen around your body.  Haemoglobin contains iron and is what turns your blood a bright red colour when it is carrying oxygen.  When you red blood cells are not carrying oxygen but are carrying carbon dioxide, your blood is a dark purple or even blue colour!  You can see this in some of your veins through your skin but as soon as your blood meets the air, the oxygen that is in the air turns it bright red.  That’s why if you ever have a cut, your blood is bright red!   

Red blood cells have a funny shape – they are a biconcave disc, that is, they look kind of like a flat donut but without the hope in the middle.  They are very flexible and can change shape very easily so they can squeeze through your very tiny capillaries.  Red blood cells are made in the middle of your bones, in your bone marrow.  They stay alive in your body, bringing oxygen to your cells by travelling around your circulatory system, for about four months.  They then die off and are replaced by new ones so that you only have the very best cells working for you all the time! 

Did you know…?

Red blood cells are the most common of all your blood cells.  They make up about 40% of your blood!

Haemoglobin makes up about one third (that’s 33%!) of your red blood cells!