Editing Red blood cell (section)

===Mammals===
[[Image:Gray453.png|thumb|300px|Typical mammalian red blood cells: (a) seen from surface; (b) in profile, forming rouleaux; (c) rendered spherical by water; (d) rendered crenate (shrunken and spiky) by salt. (c) and (d) do not normally occur in the body. The last two shapes are due to water being transported into, and out of, the cells, by [[osmosis]].]]

The red blood cells of [[mammal]]s are typically shaped as biconcave disks: flattened and depressed in the center, with a [[dumbbell]]-shaped cross section, and a [[torus]]-shaped rim on the edge of the disk. This shape allows for a high surface-area-to-volume (SA/V) ratio to facilitate diffusion of gases.<ref>{{Cite web|url=https://www.bbc.co.uk/education/guides/ztp9q6f/revision/2|title=BBC Bitesize – GCSE Biology – Blood – Revision 2|website=www.bbc.co.uk|language=en-GB|access-date=26 November 2017}}</ref> However, there are some exceptions concerning shape in the [[artiodactyl]] order (even-toed [[ungulates]] including cattle, deer, and their relatives), which displays a wide variety of bizarre red blood cell morphologies: small and highly ovaloid cells in [[llama]]s and camels (family [[Camelidae]]), tiny spherical cells in mouse deer (family [[Tragulidae]]), and cells which assume fusiform, lanceolate, crescentic, and irregularly polygonal and other angular forms in red deer and wapiti (family [[Cervidae]]). Members of this order have clearly evolved a mode of red blood cell development substantially different from the mammalian norm.<ref name="Gulliver1875" /><ref name="The bigger the C-value, the larger">{{cite journal | vauthors = Gregory TR | title = The bigger the C-value, the larger the cell: genome size and red blood cell size in vertebrates | journal = Blood Cells, Molecules & Diseases | volume = 27 | issue = 5 | pages = 830–843 | year = 2001 | pmid = 11783946 | doi = 10.1006/bcmd.2001.0457 | citeseerx = 10.1.1.22.9555 }}</ref> Overall, mammalian red blood cells are remarkably flexible and deformable so as to squeeze through tiny [[capillary|capillaries]], as well as to maximize their apposing surface by assuming a cigar shape, where they efficiently release their oxygen load.<ref>{{cite journal | vauthors = Goodman SR, Kurdia A, Ammann L, Kakhniashvili D, Daescu O | title = The human red blood cell proteome and interactome | journal = Experimental Biology and Medicine | volume = 232 | issue = 11 | pages = 1391–1408 | date = December 2007 | pmid = 18040063 | doi = 10.3181/0706-MR-156 | s2cid = 32326166 }}</ref>

Red blood cells in mammals are unique amongst vertebrates as they do not have nuclei when mature. They do have nuclei during early phases of [[erythropoiesis]], but extrude them during development as they mature; this provides more space for hemoglobin.  The red blood cells without nuclei, called [[reticulocytes]], subsequently lose all other cellular [[organelle]]s such as their [[mitochondrion|mitochondria]], [[Golgi apparatus]] and [[endoplasmic reticulum]].

The [[spleen]] acts as a reservoir of red blood cells, but this effect is somewhat limited in humans. In some other mammals such as dogs and horses, the spleen sequesters large numbers of red blood cells, which are dumped into the blood during times of exertion stress, yielding a higher oxygen transport capacity.

[[Image:Red White Blood cells.jpg|thumb|200px|Scanning electron micrograph of blood cells. From left to right: human red blood cell, [[Platelet|thrombocyte]] (platelet), [[leukocyte]].]]