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WonderBody fact

A red blood cell circulates for about 100 to 120 days, carrying oxygen from the lungs to the body. Worn-out cells are then removed and broken down, and the bone marrow makes about 2.4 million new ones every second to replace them.

Human biology

Health

The story behind the card

An adult has roughly 20 to 30 trillion red blood cells. As they mature in the bone marrow, they push out their nucleus and most of their inner machinery to make room for haemoglobin, the iron-rich protein that carries oxygen. Without a nucleus a cell cannot make new proteins or repair itself, so it slowly wears out. Old cells are swallowed by large immune cells called macrophages, mainly in the spleen and liver. The iron goes back to the bone marrow to build new cells, and the rest of the haem, the iron-holding part of haemoglobin, is turned into bilirubin, a yellow pigment that the liver releases in bile. The lifespan was first measured in 1919 by the British-born American pathologist Winifred Ashby, who tracked transfused blood cells and showed they could survive for about 110 days, far longer than the two or three weeks then assumed.

Türkçe oku
Bir alyuvar, yani kırmızı kan hücresi, akciğerlerden aldığı oksijeni vücuda taşıyarak 100-120 gün kadar dolaşır. Yıpranan hücreler kandan ayıklanıp parçalanır; kemik iliği de yerlerini doldurmak için her saniye yaklaşık 2,4 milyon yeni alyuvar üretir.

Yetişkin bir insanda kabaca 20 ila 30 trilyon alyuvar bulunur. Alyuvarlar kemik iliğinde olgunlaşır. Bu sırada çekirdeklerini ve iç yapılarının çoğunu atarak oksijeni taşıyan demirli protein hemoglobine yer açarlar. Çekirdeği olmayan hücre yeni protein üretemez, kendini onaramaz; bu yüzden zamanla yıpranır. Yaşlanan alyuvarları, çoğunlukla dalakta ve karaciğerde, makrofaj denen büyük bağışıklık hücreleri yutar. Demir kemik iliğine geri döner ve yeni hücrelerde kullanılır. Hemoglobinin demir taşıyan “hem” kısmının geri kalanı ise bilirubine dönüşür; bilirubin, karaciğerin safrayla dışarı attığı sarı bir pigmenttir. Alyuvarların ömrünü ilk kez 1919'da İngiliz asıllı Amerikalı patolog Winifred Ashby ölçtü. Nakledilen kan hücrelerini izleyerek bu hücrelerin yaklaşık 110 gün yaşayabildiğini gösterdi; o dönemde ömürlerinin iki üç hafta olduğu sanılıyordu.

Sources and further reading

Background reading: Red blood cell
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