Red blood cells, also called erythrocytes, are blood cells that carry oxygen from the lungs to body tissues and help return carbon dioxide to the lungs. They contain haemoglobin, an iron-containing protein that binds oxygen and gives blood its red colour.
Red blood cells are one of the main cellular components measured in a full blood count. Too few, too many or poorly functioning red blood cells can point to blood loss, anaemia, dehydration, bone marrow disease, inherited blood disorders or other medical conditions.
Structure
Mature human red blood cells are small, flexible cells with a biconcave disc shape. This shape gives a large surface area for gas exchange and helps the cells squeeze through narrow capillaries.
Unlike most human cells, mature red blood cells do not have a nucleus. They also lose many organelles during development. This leaves more internal space for haemoglobin, but it also means the cells cannot divide or repair themselves in the same way as nucleated cells.
Haemoglobin and Gas Transport
Haemoglobin binds oxygen in the lungs and releases it in tissues where oxygen pressure is lower. Red blood cells also carry some carbon dioxide back towards the lungs, directly and through their role in blood chemistry.
The number of red blood cells, the amount of haemoglobin and the ability of haemoglobin to bind oxygen all affect oxygen delivery. This is why anaemia can cause tiredness, breathlessness, dizziness, chest symptoms or reduced exercise tolerance.
Production
Red blood cell production is called erythropoiesis. It takes place mainly in the bone marrow. Stem cells develop through immature stages, lose their nuclei, enter the blood as reticulocytes and then mature into red blood cells.
The hormone erythropoietin, produced mainly by the kidneys, helps regulate production. When oxygen delivery is low, erythropoietin signalling can increase red blood cell production, provided the bone marrow has enough iron, vitamin B12, folate and other support.
Lifespan and Recycling
Human red blood cells usually circulate for about 120 days. Older or damaged cells are removed mostly by macrophages in the spleen, liver and bone marrow.
The body recycles much of the iron from haemoglobin for new red blood cells. Other haemoglobin components are broken down and processed, including through bilirubin metabolism.
Blood Tests
Common measurements include red blood cell count, haemoglobin, haematocrit, mean corpuscular volume and reticulocyte count. The NHS notes that normal red blood cell count ranges vary between hospital laboratories.
These tests are interpreted with symptoms, medical history and other results. A single value rarely explains the whole clinical picture.
Disorders
Red blood cell disorders include:
- Anaemia, where red blood cells or haemoglobin are too low for normal oxygen delivery.
- Iron deficiency anaemia, often linked to blood loss, low intake, pregnancy or absorption problems.
- Sickle cell disease, an inherited haemoglobin disorder that can make red blood cells rigid and sickle-shaped.
- Thalassaemia, inherited disorders affecting haemoglobin production.
- Polycythaemia, where the body has too many red blood cells.
- Haemolytic disorders, where red blood cells are destroyed too quickly.
Transfusion
Red cells can be transfused when a person needs improved oxygen-carrying capacity, such as after major blood loss or in some forms of severe anaemia. NHS guidance explains that red cells, platelets and plasma can be given as different blood components depending on what the patient needs.
See Also
References
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