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'''Red blood cells''', also called '''erythrocytes''', are blood cells that carry oxygen from the lungs to body tissues and help carry carbon dioxide back towards the lungs. They are the most numerous cells in human blood and are essential for normal oxygen delivery.
	'''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\|haemoglobin]], an iron-containing protein that binds oxygen and gives blood its red colour.

Red blood cells are specialised for transport. In humans they are small, flexible, biconcave discs with no nucleus. Their shape gives them a large surface area and helps them squeeze through tiny blood vessels.
	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 ==	== Structure ==
Mature human red blood cells do not contain a nucleus or most internal organelles. This leaves more internal space for haemoglobin, the iron-containing protein that binds oxygen. Haemoglobin also gives blood its red colour.
	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.

The biconcave shape is important. It helps red blood cells pass through capillaries and improves gas exchange. Their membrane is flexible, but it can be damaged by inherited conditions, immune attack, infection, toxins, or mechanical stress.
	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.

== Function ==
The main function of a red blood cell is gas transport. In the lungs, oxygen binds to haemoglobin. In body tissues, where oxygen levels are lower, haemoglobin releases oxygen so cells can use it in metabolism.
	== 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.

Red blood cells also help carry carbon dioxide away from tissues. Some carbon dioxide binds to haemoglobin, but much of it is carried in the blood as bicarbonate after conversion by enzymes inside red blood cells. This means red blood cells also help maintain blood acidity within a narrow range.
	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 ==	== Production ==
Red blood cell production is called erythropoiesis. It takes place mainly in the bone marrow. The process begins with blood-forming stem cells and passes through several immature stages before reticulocytes enter the bloodstream and mature.
	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.

Erythropoietin, often shortened to EPO, is a hormone that stimulates red blood cell production. The kidneys produce more erythropoietin when oxygen delivery is low. Merck Manual states that red blood cell production also needs enough iron, vitamin B12, folate, and haem.
	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 ==	== Lifespan and Recycling ==
A typical human red blood cell circulates for about 120 days. Old or damaged cells are removed mainly by macrophages in the spleen, liver, and bone marrow. Useful material is recycled. Iron from haemoglobin can be stored and reused to make new red blood cells.
	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.

This recycling is constant because the body makes and removes large numbers of red blood cells every day. Problems with production, destruction, or blood loss can quickly affect oxygen delivery.
	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 ==	== Blood Tests ==
Red blood cells are measured in common blood tests. A full blood count may include red blood cell count, haemoglobin concentration, haematocrit, mean cell volume, and other indices. These results help clinicians assess anaemia, blood loss, dehydration, inflammation, kidney disease, nutritional deficiency, inherited blood disorders, and bone marrow problems.

Laboratory values need clinical context. A single abnormal result can have several possible causes, and normal ranges can differ by age, sex, pregnancy, altitude, laboratory method, and medical history.

== Related Conditions ==
Red blood cell problems include:
	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.

* [[Anemia\|Anaemia]], where the blood has too little haemoglobin or too few effective red blood cells.
* Iron-deficiency anaemia, often linked to blood loss, diet, pregnancy, absorption problems, or inflammation.
* Sickle cell disease, where abnormal haemoglobin can make red blood cells rigid and sickle-shaped.
* [[Thalassemia\|Thalassaemia]], a group of inherited disorders affecting haemoglobin production.
* Haemolysis, where red blood cells are destroyed too quickly.
* Polycythaemia, where red blood cell mass is abnormally high.
	These tests are interpreted with symptoms, medical history and other results. A single value rarely explains the whole clinical picture.

Kidney disease can contribute to anaemia because damaged kidneys may not make enough erythropoietin. The National Heart, Lung, and Blood Institute notes this relationship in its patient information on iron-deficiency anaemia and related causes.
	== Disorders ==
	Red blood cell disorders include:

== Terminology ==
The word erythrocyte comes from Greek roots meaning red cell. In everyday language, red blood cell is clearer. In medical writing, RBC is often used as an abbreviation.
	* '''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.

The protein name is written '''haemoglobin''' in British English and '''hemoglobin''' in American English. Both refer to the same oxygen-binding protein.
	== 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 ==	== See Also ==
* [[Anemia]]
* [[Hemoglobin]]
* [[Thalassemia]]
* [[Virus]]
	* [[White_Blood_Cells]]
	* [[Platelets]]
	* [[Anaemia]]
	* [[Sickle_Cell_Disease]]

== References ==	== References ==
	* [https://www.nhs.uk/tests-and-treatments/red-blood-count/ NHS: Red blood cell count]
	* [https://www.blood.co.uk/news-and-campaigns/the-donor/latest-stories/functions-of-blood-transport-around-the-body/ NHS Blood Donation: Functions of blood]
* [https://www.ncbi.nlm.nih.gov/books/NBK539702/ NCBI Bookshelf: Histology, Red Blood Cell]	* [https://www.ncbi.nlm.nih.gov/books/NBK539702/ NCBI Bookshelf: Histology, Red Blood Cell]
* [https://www.merckmanuals.com/professional/hematology-and-oncology/approach-to-the-patient-with-anemia/red-blood-cell-production Merck Manual Professional Edition: Red Blood Cell Production]
* [https://www.nhlbi.nih.gov/health/anemia/iron-deficiency-anemia NHLBI: Iron-Deficiency Anemia]
	* [https://medlineplus.gov/lab-tests/red-blood-cell-rbc-count/ MedlinePlus: Red blood cell count]
	* [https://www.nhs.uk/tests-and-treatments/blood-transfusion/ NHS: Blood transfusion]

[[Category:Medicine]]
[[Category:Biology]]	[[Category:Biology]]
[[Category:Blood]]
	[[Category:Medicine]]