Red blood cell: Difference between revisions

{{Use dmy dates|date=December 2020}}

{{Infobox cell

| Name = Red blood cells

| Latin=

| Image2 =

| Caption2 =

| Function = [[Oxygen]] transport

}}

 

The [[cytoplasm]] of a red blood cell is rich in [[hemoglobin]], an [[iron]]-containing [[biomolecule]] that can bind oxygen and is responsible for the red color of the cells and the blood. Each human red blood cell contains approximately 270&nbsp;million hemoglobin molecules.<ref>{{cite journal | vauthors = D'Alessandro A, Dzieciatkowska M, Nemkov T, Hansen KC | title = Red blood cell proteomics update: is there more to discover? | journal = Blood Transfusion = Trasfusione del Sangue | volume = 15 | issue = 2 | pages = 182–187 | date = March 2017 | pmid = 28263177 | pmc = 5336341 | doi = 10.2450/2017.0293-16 }}</ref> The [[cell membrane]] is composed of [[proteins]] and [[lipids]], and this structure provides properties essential for physiological [[Cell (biology)|cell]] function such as [[erythrocyte deformability|deformability]] and [[erythrocyte fragility|stability]] of the blood cell while traversing the circulatory system and specifically the [[capillary]] network.

In humans, mature red blood cells are flexible [[biconcave disk]]s. They lack a [[cell nucleus]] (which is expelled during [[Erythropoiesis|development]]) and [[organelle]]s, to accommodate maximum space for hemoglobin; they can be viewed as sacks of hemoglobin, with a [[lipid bilayer|plasma membrane]] as the sack. Approximately 2.4&nbsp;million new erythrocytes are produced per second in human adults.<ref name="Sackmann">[[Erich Sackmann]], ''Biological Membranes Architecture and Function.'', Handbook of Biological Physics, (ed. R.Lipowsky and E.Sackmann, vol.1, Elsevier, 1995</ref> The cells develop in the [[bone marrow]] and circulate for about 100–120 days in the body before their components are recycled by [[macrophage]]s. Each circulation takes about 60 seconds (one minute).<ref name="Blom20032">{{cite book|url=https://books.google.com/books?id=CJ4c6gbewfQC&pg=PA27|title=Monitoring of Respiration and Circulation|year= 2003|publisher=CRC Press|isbn=978-0-203-50328-7|page=27| vauthors = Blom JA }}</ref> Approximately 84% of the cells in the human body are the 20–30&nbsp;trillion red blood cells.<ref>{{cite journal | vauthors = Hatton IA, Galbraith ED, Merleau NS, Miettinen TP, Smith BM, Shander JA | title = The human cell count and size distribution | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 120 | issue = 39 | pages = e2303077120 | date = September 2023 | pmid = 37722043 | pmc = 10523466 | doi = 10.1073/pnas.2303077120 | bibcode = 2023PNAS..12003077H }}</ref><ref>{{cite journal | vauthors = Sender R, Fuchs S, Milo R | title = Revised Estimates for the Number of Human and Bacteria Cells in the Body | journal = PLOS Biology | volume = 14 | issue = 8 | pages = e1002533 | date = August 2016 | pmid = 27541692 | pmc = 4991899 | doi = 10.1371/journal.pbio.1002533 | doi-access = free }}</ref><ref name="dean">{{Cite book| vauthors = Dean L | url=https://www.ncbi.nlm.nih.gov/books/NBK2261/?depth=2| title = Blood Groups and Red Cell Antigens|date=2005|publisher=National Center for Biotechnology Information (US)}}</ref><ref name="pierige">{{cite journal | vauthors = Pierigè F, Serafini S, Rossi L, Magnani M | title = Cell-based drug delivery | journal = Advanced Drug Delivery Reviews | volume = 60 | issue = 2 | pages = 286–295 | date = January 2008 | pmid = 17997501 | doi = 10.1016/j.addr.2007.08.029 }}</ref> Nearly half of the blood's volume ([[hematocrit|40% to 45%]]) is red blood cells.

 

 

== Structure ==

[[Image:Erytrocyte deoxy to oxy v0.7.gif|thumb|200px|Animation of a typical human red blood cell cycle in the circulatory system. This animation occurs at a faster rate (~20 seconds of the average 60-second cycle) and shows the red blood cell deforming as it enters capillaries, as well as the bars changing color as the cell alternates in states of oxygenation along the circulatory system.]]

 

 

Adult humans have roughly 20–30&nbsp;trillion red blood cells at any given time, constituting approximately 70% of all cells by number.<ref>{{cite journal | vauthors = Bianconi E, Piovesan A, Facchin F, Beraudi A, Casadei R, Frabetti F, Vitale L, Pelleri MC, Tassani S, Piva F, Perez-Amodio S, Strippoli P, Canaider S | display-authors = 6 | title = An estimation of the number of cells in the human body | journal = Annals of Human Biology | volume = 40 | issue = 6 | pages = 463–471 | date = 1 November 2013 | pmid = 23829164 | doi = 10.3109/03014460.2013.807878 | s2cid = 16247166 | doi-access = free | hdl = 11585/152451 }}</ref> Women have about 4–5&nbsp;million red blood cells per microliter (cubic millimeter) of blood and men about 5–6&nbsp;million; [[Effects of high altitude on humans#Acclimatization|people living at high altitudes]] with low oxygen tension will have more. Red blood cells are thus much more common than the other blood particles: there are about 4,000–11,000 [[white blood cells]] and about 150,000–400,000 [[platelet]]s per microliter.

==Microstructure==

===Nucleus===

 

The elimination of the nucleus in vertebrate red blood cells has been offered as an explanation for the subsequent [[C-value enigma|accumulation of non-coding DNA in the genome]].<ref name="The bigger the C-value, the larger"/> The argument runs as follows: Efficient gas transport requires red blood cells to pass through very narrow capillaries, and this constrains their size. In the absence of nuclear elimination, the accumulation of repeat sequences is constrained by the volume occupied by the nucleus, which increases with genome size.