Editing Haematopoiesis (section)

==Location==
{{main|Haematopoietic system}}
[[Image:Hematopoesis EN.svg|thumb|350px|Sites of haematopoiesis (human) in pre- and postnatal periods]]
In developing embryos, blood formation occurs in aggregates of blood cells in the yolk sac, called [[blood islands]]. As development progresses, blood formation occurs in the [[spleen]], [[liver]] and [[lymph nodes]].<ref name="Embrio_Hematopoiesis">{{Cite journal |last=Singh |first=Ranbir |last2=Soman-Faulkner |first2=Kristina |last3=Sugumar |first3=Kavin |year=2022 |title=Embryology, Hematopoiesis |url=https://www.ncbi.nlm.nih.gov/books/NBK544245/ |publisher=StatPearls |pmid=31334965 |access-date=4 September 2022 |website=NCBI}}</ref> When [[bone marrow]] develops, it eventually assumes the task of forming most of the blood cells for the entire organism.<ref name="Birbrair n/a–n/a"/> However, maturation, activation, and some proliferation of lymphoid cells occurs in the spleen, [[thymus]], and lymph nodes. In children, haematopoiesis occurs in the marrow of the long bones such as the femur and tibia. In adults, it occurs mainly in the pelvis, cranium, vertebrae, and sternum.<ref>{{Cite journal |vauthors=Fernández KS, de Alarcón PA |date=Dec 2013 |title=Development of the hematopoietic system and disorders of hematopoiesis that present during infancy and early childhood. |url=https://www.sciencedirect.com/science/article/abs/pii/S0031395513001132 |journal=Pediatric Clinics of North America |volume=60 |issue=6 |pages=1273–89 |doi=10.1016/j.pcl.2013.08.002 |pmid=24237971 |url-access=limited}}</ref>

===Extramedullary===
In some cases, the liver, thymus, and spleen may resume their haematopoietic function, if necessary. This is called ''[[extramedullary hematopoiesis|extramedullary haematopoiesis]]''. It may cause these organs to increase in size substantially. During fetal development, since bones and thus the bone marrow develop later, the liver functions as the main haematopoietic organ. Therefore, the liver is enlarged during development.<ref>{{Cite journal |vauthors=Georgiades CS, Neyman EG, Francis IR, Sneider MB, Fishman EK |date=Nov 2002 |title=Typical and atypical presentations of extramedullary hemopoiesis. |journal=AJR. American Journal of Roentgenology |volume=179 |issue=5 |pages=1239–43 |doi=10.2214/ajr.179.5.1791239 |pmid=12388506 |doi-access=free}}</ref> Extramedullary haematopoiesis and myelopoiesis may supply [[leukocytes]] in [[cardiovascular disease]] and inflammation during adulthood.<ref>{{Cite journal |last=Swirski |first=Filip K. |last2=Libby |first2=Peter |last3=Aikawa |first3=Elena |last4=Alcaide |first4=Pilar |last5=Luscinskas |first5=F. William |last6=Weissleder |first6=Ralph |last7=Pittet |first7=Mikael J. |date=2 January 2007 |title=Ly-6Chi monocytes dominate hypercholesterolemia-associated monocytosis and give rise to macrophages in atheromata |journal=Journal of Clinical Investigation |volume=117 |issue=1 |pages=195–205 |doi=10.1172/JCI29950 |pmc=1716211 |pmid=17200719 |doi-access=free}}</ref><ref>{{Cite journal |vauthors=Swirski FK, Nahrendorf M, Etzrodt M, Wildgruber M, Cortez-Retamozo V, Panizzi P, Figueiredo JL, Kohler RH, Chudnovskiy A, Waterman P, Aikawa E, Mempel TR, Libby P, Weissleder R, Pittet MJ |date=30 July 2009 |title=Identification of Splenic Reservoir Monocytes and Their Deployment to Inflammatory Sites |journal=Science |volume=325 |issue=5940 |pages=612–616 |bibcode=2009Sci...325..612S |doi=10.1126/science.1175202 |pmc=2803111 |pmid=19644120}}</ref> Splenic [[macrophages]] and [[adhesion molecules]] may be involved in regulation of extramedullary myeloid cell generation in [[cardiovascular disease]].<ref>{{Cite journal |last=Dutta |first=P |last2=Hoyer |first2=FF |last3=Grigoryeva |first3=LS |last4=Sager |first4=HB |last5=Leuschner |first5=F |last6=Courties |first6=G |last7=Borodovsky |first7=A |last8=Novobrantseva |first8=T |last9=Ruda |first9=VM |last10=Fitzgerald |first10=K |last11=Iwamoto |first11=Y |last12=Wojtkiewicz |first12=G |last13=Sun |first13=Y |last14=Da Silva |first14=N |last15=Libby |first15=P |date=6 April 2015 |title=Macrophages retain hematopoietic stem cells in the spleen via VCAM-1. |journal=The Journal of Experimental Medicine |volume=212 |issue=4 |pages=497–512 |doi=10.1084/jem.20141642 |pmc=4387283 |pmid=25800955 |doi-access=free |first17=FK |last18=Weissleder |first18=R |last19=Nahrendorf |first19=M |last17=Swirski |first16=DG |last16=Anderson}}</ref><ref>{{Cite journal |last=Dutta |first=P |last2=Hoyer |first2=FF |last3=Sun |first3=Y |last4=Iwamoto |first4=Y |last5=Tricot |first5=B |last6=Weissleder |first6=R |last7=Magnani |first7=JL |last8=Swirski |first8=FK |last9=Nahrendorf |first9=M |date=September 2016 |title=E-Selectin Inhibition Mitigates Splenic HSC Activation and Myelopoiesis in Hypercholesterolemic Mice With Myocardial Infarction. |journal=Arteriosclerosis, Thrombosis, and Vascular Biology |volume=36 |issue=9 |pages=1802–8 |doi=10.1161/ATVBAHA.116.307519 |pmc=5001901 |pmid=27470513 |doi-access=free}}</ref>