Editing Capillary (section)

== History ==
A 13th century [[Commentary on Anatomy in Avicenna's Canon|manuscript by Ibn Nafis]] contains the earliest known description of capillaries. The manuscript records Ibn Nafis' prediction of the existence of the capillaries which he described as perceptible passages (''manafidh'') between pulmonary artery and pulmonary vein. These passages would later be identified by [[Marcello Malpighi]] as capillaries. He further states that the heart's two main chambers (right and left ventricles) are separate and that blood cannot pass through the (interventricular) septum.<ref>{{Cite journal |last=West |first=John B. |date=2008 |title=Ibn al-Nafis, the pulmonary circulation, and the Islamic Golden Age |journal=Journal of Applied Physiology |language=en |volume=105 |issue=6 |pages=1877–1880 |doi=10.1152/japplphysiol.91171.2008 |issn=8750-7587 |pmc=2612469 |pmid=18845773}}</ref><ref>{{Cite journal |last=Aloud |first=Abdurahim |date=2017-01-16 |title=Ibn al-Nafis and the discovery of the pulmonary circulation |url=https://pulmonarychronicles.com/index.php/pulmonarychronicles/article/view/377/823 |journal=The Southwest Respiratory and Critical Care Chronicles |language=en |volume=5 |issue=17 |pages=71–73 |doi=10.12746/swrccc2017.0517.229 |issn=2325-9205}}</ref>

[[William Harvey]] did not explicitly predict the existence of capillaries, but he saw the need for some sort of connection between the arterial and venous systems. In 1653, he wrote, "...the blood doth enter into every member through the arteries, and does return by the veins, and that the veins are the vessels and ways by which the blood is returned to the heart itself; and that the blood in the members and extremities does pass from the arteries into the veins (either mediately by an anastomosis, or immediately through the porosities of the flesh, or both ways) as before it did in the heart and thorax out of the veins, into the arteries..."<ref>{{cite book|last1=Harvey|first1=William|title=On the motion of the Heart and Blood in Animals|date=1653|pages=59–60|url=http://hos.ou.edu/galleries//17thCentury/Harvey/1653/|archive-url=https://web.archive.org/web/20111201202313/http://hos.ou.edu/galleries//17thCentury/Harvey/1653/ |archive-date=1 December 2011 }}</ref>

[[Marcello Malpighi]] was the first to observe directly and correctly describe capillaries, discovering them in a frog's lung 8 years later, in 1661.<ref>{{cite book | title = Blood Vessels | last = Cliff|first= Walter John | date = 1976 | publisher = Cambridge University Press | page = 14|isbn=9780835773287}}</ref>

[[August Krogh]] discovered how capillaries provide nutrients to animal tissue. For his work he was awarded the 1920 [[Nobel Prize in Physiology or Medicine]].<ref>{{cite web|url=https://www.nobelprize.org/prizes/medicine/1920/krogh/biographical/|title=August Krogh|date=July 2023}}</ref> His 1922 estimate that total length of capillaries in a human body is as long as 100,000 km, had been widely adopted by textbooks and other secondary sources. This estimate was based on figures he gathered from "an extraordinarily large person".<ref name=":0">{{Cite web |last=Poole |first=David C |last2=Kano |first2=Yutaka |last3=Shunsaku |first3=Koga |last4=Musch |first4=Timothy I |title=August Krogh: Muscle capillary function and oxygen delivery |url=https://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC7867635&blobtype=pdf |access-date=2024-10-30 |page=8}}</ref> More recent estimates give a number between 9,000 and 19,000 km.<ref>{{Cite web |last=Kurzgesagt |title=Sources - 100K Blood Vessels |url=https://sites.google.com/view/sources-100k-blood-vessels |access-date=2024-10-29 |website=sites.google.com |language=en-US}}</ref><ref name=":0" />