{{Short description|Inner layer of blood vessel}} {{No footnotes|article|date=May 2015}} {{Infobox anatomy | Name = Tunica intima | Latin = tunica intima | Greek = | Image = File:Blausen 0055 ArteryWallStructure.png | Caption = | Width = | Image2 = Gray448.png | Caption2 = Transverse section through a small [[artery]] and [[vein]] of the [[mucous membrane]] of the [[epiglottis]] of a child. (Tunica intima is at "e".) | Precursor = | System = | Artery = | Vein = | Nerve = | Lymph = | part_of = Wall of [[blood vessel]]s }} The '''tunica intima''' ([[Neo-Latin]] "inner coat"), or '''intima''' for short, is the innermost [[tunica (biology)|tunica]] (layer) of an [[artery]] or [[vein]]. It is made up of one layer of [[endothelium|endothelial cell]]s (and macrophages in areas of disturbed blood flow),<ref name=":0">{{Cite journal |last1=Scipione |first1=Corey A. |last2=Hyduk |first2=Sharon J. |last3=Polenz |first3=Chanele K. |last4=Cybulsky |first4=Myron I. |date=December 2023 |title=Unveiling the Hidden Landscape of Arterial Diseases at Single-Cell Resolution |url=https://linkinghub.elsevier.com/retrieve/pii/S0828282X2301663X |journal=Canadian Journal of Cardiology |language=en |volume=39 |issue=12 |pages=1781–1794 |doi=10.1016/j.cjca.2023.09.009|pmid=37716639 |url-access=subscription }}</ref><ref>{{Cite journal |last1=Scipione |first1=Corey A. |last2=Cybulsky |first2=Myron I. |date=October 2022 |title=Early atherogenesis: new insights from new approaches |journal=Current Opinion in Lipidology |language=en |volume=33 |issue=5 |pages=271–276 |doi=10.1097/MOL.0000000000000843 |issn=0957-9672 |pmc=9594136 |pmid=35979994}}</ref> and is supported by an [[internal elastic lamina]]. The endothelial cells are in direct contact with the [[blood flow]].
The three layers of a blood vessel are an inner layer (the tunica intima), a middle layer (the [[tunica media]]), and an outer layer (the [[tunica externa]]).
In [[dissection]], the inner coat (tunica intima) can be separated from the middle (tunica media) by a little maceration, or it may be stripped off in small pieces; but, because of its friability, it cannot be separated as a complete membrane. It is a fine, transparent, colorless structure which is highly elastic, and, after death, is commonly corrugated into longitudinal wrinkles.
==Structure== The structure of the tunica intima depends on the blood vessel type.<ref name=sp>{{Cite web|last1=Steve|first1=Paxton|last2=Michelle|first2=Peckham|last3=Adele|first3=Knibbs|date=2003|title=The Leeds Histology Guide|url=https://www.histology.leeds.ac.uk/circulatory/arteries.php|language=en}}</ref>
'''[[Elastic artery|Elastic arteries]]''' – A single layer of [[Endothelium|endothelial]] and a supporting layer of [[elastin]]-rich [[collagen]]. The layer also contains [[fibroblast]]s, immune cells and [[Smooth muscle|smooth muscle cells]].<ref name=":0" />
'''[[Distributing artery|Muscular arteries]]''' – [[Endothelium|Endothelial]] cells
'''[[Arteriole]]s''' – A single layer of [[Endothelium|endothelial]] cells
'''[[Vein]]s''' – [[Endothelium|Endothelial]] cells<ref name=sp/> The inner coat consists of:
# A layer of pavement [[endothelium]], the cells of which are polygonal, oval, or fusiform, and have very distinct round or oval nuclei. This endothelium is brought into view most distinctly by staining with [[silver nitrate]]. # A subendothelial layer, consisting of delicate connective tissue with branched cells lying in the interspaces of the tissue; in arteries of less than 2 mm in diameter the subendothelial layer consists of a single stratum of [[stellate cells]], and the [[connective tissue]] is only largely developed in vessels of a considerable size.{{Citation needed|date=May 2017}} # An elastic or [[fenestra]]ted layer, which consists of a membrane containing a network of elastic fibers, having principally a longitudinal direction, and in which, under the microscope, small elongated apertures or perforations may be seen, giving it a fenestrated appearance. It was therefore called by Henle the ''fenestrated membrane''. This membrane forms the chief thickness of the inner coat, and can be separated into several layers, some of which present the appearance of a network of longitudinal elastic fibers, and others a more membranous character, marked by pale lines having a longitudinal direction. In minute arteries the fenestrated membrane is a very thin layer; but in the larger arteries, and especially in the [[aorta]], it has a considerable thickness.
==Function== Endothelium had been seen to be simply the boundary between the blood in the lumen and the walls of the vessels. However, endothelium has been shown to release local chemicals called [[endothelin]]s which are powerful [[vasoconstrictor]]s.<ref name="Haryono">{{cite journal |last1=Haryono |first1=A |last2=Ramadhiani |first2=R |last3=Ryanto |first3=GRT |last4=Emoto |first4=N |title=Endothelin and the Cardiovascular System: The Long Journey and Where We Are Going. |journal=Biology |date=16 May 2022 |volume=11 |issue=5 |page=759 |doi=10.3390/biology11050759 |pmid=35625487|pmc=9138590 |doi-access=free }}</ref> Endothelins help to regulate capillary exchange and alter blood flow by their constriction of the smooth muscle in the walls. Vasoconstriction increases [[blood pressure]], and its [[overexpression]] can contribute to [[hypertension]] and [[cardiovascular disease]].<ref name="Openstax Anatomy & Physiology attribution">{{CC-notice|cc=by4|url=https://openstax.org/books/anatomy-and-physiology/pages/20-1-structure-and-function-of-blood-vessels}} {{cite book|last1=Betts|first1=J Gordon|last2=Desaix|first2=Peter|last3=Johnson|first3=Eddie|last4=Johnson|first4=Jody E|last5=Korol|first5=Oksana|last6=Kruse|first6=Dean|last7=Poe|first7=Brandon|last8=Wise|first8=James|last9=Womble|first9=Mark D|last10=Young|first10=Kelly A|title=Anatomy & Physiology|location=Houston|publisher=OpenStax CNX|isbn=978-1-947172-04-3|date=June 8, 2023|at=20.1 Structure and function of blood vessels}}</ref>
==Additional images== <gallery> Image:Illu vein.jpg|Vein Image:Calcificatio atherosclerotica.jpg|Microphotography of arterial wall with calcified (violet colour) atherosclerotic plaque (H&E stain) </gallery>
== References == {{Gray's}} {{Reflist}}
== External links == * {{OklahomaHistology|66_02}} – "Aorta" * {{UCDavisOrganology|Circulatory/vessels/vessels7/vessels2}} — "Bird, vessels (LM, High)" * [http://biology.about.com/library/organs/heart/bltunica3.htm Image at About.com]
{{Arteries and veins}} {{Portal bar|Anatomy}} {{Authority control}}
[[Category:Arteries]] [[Category:Cardiovascular system anatomy]]