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Wikipedia states that a cell is

the basic structural, functional and biological unit of all known living organisms. Cells are the smallest unit of life that can replicate independently.

It then goes on to state that

All cells (except red blood cells which lack a cell nucleus and most organelles to accommodate maximum space for hemoglobin) possess DNA.

Then why are red blood cells still considered cells, while they can't replicate? Is the definition on Wikipedia just a bad definition? Or are red blood cells wrongly considered cells, but remain so for historical reasons? Or are they considered cells for some other reason, such as this answer which states that red blood cells do contain a nucleus at some point?

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  • $\begingroup$ that's why they are referred to as corpuscles $\endgroup$
    – WYSIWYG
    Commented May 10, 2014 at 7:07
  • $\begingroup$ Many fully differentiated cells can't replicate: neurons, for example. $\endgroup$
    – Alan Boyd
    Commented May 10, 2014 at 12:10
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    $\begingroup$ Animals such as birds and amphibians have nucleated red blood cells... $\endgroup$
    – PlaysDice
    Commented May 10, 2014 at 12:33
  • $\begingroup$ The most prominent other non-nucleated corupscules are platelets. If you consider why they aren't called "cells", you'd arrive at the conclusion that it's something to do with one RBC originating from one precursor by eliminating its nucleus, rather than one precursor producing lots of non-nucleated membrane bubbles (i.e. megakaryocytes). Then again, jargon calls platelets thrombo-"cytes" ;) $\endgroup$
    – Armatus
    Commented May 11, 2014 at 13:13

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A very good question, and it is most likely because of the last option. It had a nucleus for part of its life. After the RBC jettisons its nucleus, it still remains very metabolically active for approximately 3 months. It maintains its cell membrane integrity, it metabolizes glucose, it interacts constantly with its environment, numerous cellular functions and structure remain intact... It is extremely specialized for a primary purpose, and no longer requires the nucleus to provide more proteins. It has limited capacity to heal from injury, so it has a limited life span.

Speculation: I wonder if it might lose the nucleus early on so that when it is destroyed in the spleen at the end of its life as RBCs are, the spleen macrophages are not overwhelmed with additional processing of nucleic acids? Macrophage type cells are already working hard in there to clear infectious agents and some immune cells from the blood.

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    $\begingroup$ I'd say it's much more likely eliminated simply to free up the space. The nucleus is a massive organelle and takes away lots of space the cell could fill up with haemoglobin. $\endgroup$
    – Armatus
    Commented May 11, 2014 at 13:09
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    $\begingroup$ I definitely agree with @Armatus about space being the likeliest explanation for the early loss of the nucleus. Also keep in mind that the total "nuclear flux" (and the processing load of the waste from that flux) would be the same whether the nuclei were lost early or lost late $\endgroup$
    – tel
    Commented Nov 10, 2015 at 19:34

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