tunica externa
{{Short description|Outer layer of blood vessel}}
{{Infobox anatomy
| Name = Tunica externa
| Latin = tunica externa, tunica adventitia
| Image = Blausen 0055 ArteryWallStructure.png
| Width = 250
| Caption =
| Image2 = Illu artery.jpg
| Caption2 = Section of a medium-sized artery.
| Precursor =
| System =
| Artery =
| Vein =
| part_of = Wall of blood vessels
| Nerve =
| Lymph =
}}
The tunica externa (Neo-Latin "outer coat"), also known as the tunica adventitia (Neo-Latin "additional coat"),{{Citation|last=Maleszewski|first=J. J.|title=Chapter 1 - Anatomic Considerations and Examination of Cardiovascular Specimens (Excluding Devices)|date=2016-01-01|url=http://www.sciencedirect.com/science/article/pii/B978012420219100001X|work=Cardiovascular Pathology (Fourth Edition)|pages=1–56|editor-last=Buja|editor-first=L. Maximilian|place=San Diego|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-420219-1.00001-x|isbn=978-0-12-420219-1|access-date=2020-12-29|last2=Lai|first2=C. K.|last3=Veinot|first3=J. P.|editor2-last=Butany|editor2-first=Jagdish|url-access=subscription}} is the outermost tunica (layer) of a blood vessel, surrounding the tunica media. It is mainly composed of collagen and, in arteries, is supported by external elastic lamina. The collagen serves to anchor the blood vessel to nearby organs, giving it stability.
The three layers of the blood vessels are: an inner tunica intima, a middle tunica media, and an outer tunica externa.
Structure
The tunica externa is made from collagen and elastic fibers in a loose connective tissue. This is secreted by fibroblasts.{{Citation|last=Hunt|first=J. M.|title=Pulmonary Hypertension/Pulmonary Arterial Hypertension|date=2014-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780123864567053065|work=Pathobiology of Human Disease|pages=2625–2635|editor-last=McManus|editor-first=Linda M.|place=San Diego|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-386456-7.05306-5|isbn=978-0-12-386457-4|access-date=2020-12-29|last2=Graham|first2=B. B.|editor2-last=Mitchell|editor2-first=Richard N.|url-access=subscription}} This is normally the thickest tunic in veins and may be thicker than the tunica media in some larger arteries. The outer layers of the tunica externa are not distinct but rather blend with the surrounding connective tissue outside the vessel, helping to hold the vessel in relative position.{{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}}
Function
The tunica externa provides basic structural support to blood vessels. It prevents vessels from expanding too much from internal blood pressure, particularly arteries. It is also relevant in controlling vascular flow in the lungs.
Clinical significance
A common pathological disorder concerning the tunica externa is scurvy, also known as vitamin C deficiency. Scurvy occurs because vitamin C is essential for the synthesis of collagen, and without it, the faulty collagen cannot maintain the vein walls and rupture, leading to a multitude of problems.{{cn|date=July 2024}}
Additional images
File:Gray448.png|Transverse section through a small artery and vein of the mucous membrane of the epiglottis of a child. (Tunica adventitia is at 'a'.)
File:Calcificatio atherosclerotica.jpg|Microphotography of arterial wall with calcified (violet colour) atherosclerotic plaque (H&E stain)
See also
References
{{Gray's}}
{{Reflist}}
External links
- {{UCDavisOrganology|Circulatory/vessels/vessels7/vessels4}} - "Bird, vessels (LM, High)"
{{Cardiovascular system}}
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