# Tunica intima

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Inner layer of blood vessel

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Tunica intima Transverse section through a small artery and vein of the mucous membrane of the epiglottis of a child. (Tunica intima is at "e".) Details Part of Wall of blood vessels Identifiers Latin tunica intima MeSH D017539 TA98 A12.0.00.018 TA2 3922 TH H3.09.02.0.01003 FMA 55589 Anatomical terminology [edit on Wikidata]

The **tunica intima** ([Neo-Latin](/source/Neo-Latin) "inner coat"), or **intima** for short, is the innermost [tunica](/source/Tunica_(biology)) (layer) of an [artery](/source/Artery) or [vein](/source/Vein). It is made up of one layer of [endothelial cells](/source/Endothelium) (and macrophages in areas of disturbed blood flow),[1][2] and is supported by an [internal elastic lamina](/source/Internal_elastic_lamina). The endothelial cells are in direct contact with the [blood flow](/source/Blood_flow).

The three layers of a blood vessel are an inner layer (the tunica intima), a middle layer (the [tunica media](/source/Tunica_media)), and an outer layer (the [tunica externa](/source/Tunica_externa)).

In [dissection](/source/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.[3]

**[Elastic arteries](/source/Elastic_artery)** – A single layer of [endothelial](/source/Endothelium) and a supporting layer of [elastin](/source/Elastin)-rich [collagen](/source/Collagen). The layer also contains [fibroblasts](/source/Fibroblast), immune cells and [smooth muscle cells](/source/Smooth_muscle).[1]

**[Muscular arteries](/source/Distributing_artery)** – [Endothelial](/source/Endothelium) cells

**[Arterioles](/source/Arteriole)** – A single layer of [endothelial](/source/Endothelium) cells

**[Veins](/source/Vein)** – [Endothelial](/source/Endothelium) cells[3]

The inner coat consists of:

1. A layer of pavement [endothelium](/source/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](/source/Silver_nitrate).

1. 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](/source/Stellate_cells), and the [connective tissue](/source/Connective_tissue) is only largely developed in vessels of a considerable size.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

1. An elastic or [fenestrated](/source/Fenestra) 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](/source/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 [endothelins](/source/Endothelin) which are powerful [vasoconstrictors](/source/Vasoconstrictor).[4] Endothelins help to regulate capillary exchange and alter blood flow by their constriction of the smooth muscle in the walls. Vasoconstriction increases [blood pressure](/source/Blood_pressure), and its [overexpression](/source/Overexpression) can contribute to [hypertension](/source/Hypertension) and [cardiovascular disease](/source/Cardiovascular_disease).[5]

## Additional images

		- Vein

		- Microphotography of arterial wall with calcified (violet colour) atherosclerotic plaque (H&E stain)

## References

*This article incorporates text in the [public domain](/source/Public_domain) from [page 498](https://archive.org/stream/anatomyofhumanbo1918gray#page/498/mode/2up) of the 20th edition of* [Gray's Anatomy](/source/Gray's_Anatomy) *(1918)*

1. ^ [***a***](#cite_ref-:0_1-0) [***b***](#cite_ref-:0_1-1) Scipione, Corey A.; Hyduk, Sharon J.; Polenz, Chanele K.; Cybulsky, Myron I. (December 2023). ["Unveiling the Hidden Landscape of Arterial Diseases at Single-Cell Resolution"](https://linkinghub.elsevier.com/retrieve/pii/S0828282X2301663X). *Canadian Journal of Cardiology*. **39** (12): 1781–1794. [doi](/source/Doi_(identifier)):[10.1016/j.cjca.2023.09.009](https://doi.org/10.1016%2Fj.cjca.2023.09.009). [PMID](/source/PMID_(identifier)) [37716639](https://pubmed.ncbi.nlm.nih.gov/37716639).

1. **[^](#cite_ref-2)** Scipione, Corey A.; Cybulsky, Myron I. (October 2022). ["Early atherogenesis: new insights from new approaches"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9594136). *Current Opinion in Lipidology*. **33** (5): 271–276. [doi](/source/Doi_(identifier)):[10.1097/MOL.0000000000000843](https://doi.org/10.1097%2FMOL.0000000000000843). [ISSN](/source/ISSN_(identifier)) [0957-9672](https://search.worldcat.org/issn/0957-9672). [PMC](/source/PMC_(identifier)) [9594136](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9594136). [PMID](/source/PMID_(identifier)) [35979994](https://pubmed.ncbi.nlm.nih.gov/35979994).

1. ^ [***a***](#cite_ref-sp_3-0) [***b***](#cite_ref-sp_3-1) Steve, Paxton; Michelle, Peckham; Adele, Knibbs (2003). ["The Leeds Histology Guide"](https://www.histology.leeds.ac.uk/circulatory/arteries.php).

1. **[^](#cite_ref-Haryono_4-0)** Haryono, A; Ramadhiani, R; Ryanto, GRT; Emoto, N (16 May 2022). ["Endothelin and the Cardiovascular System: The Long Journey and Where We Are Going"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9138590). *Biology*. **11** (5): 759. [doi](/source/Doi_(identifier)):[10.3390/biology11050759](https://doi.org/10.3390%2Fbiology11050759). [PMC](/source/PMC_(identifier)) [9138590](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9138590). [PMID](/source/PMID_(identifier)) [35625487](https://pubmed.ncbi.nlm.nih.gov/35625487).

1. **[^](#cite_ref-Openstax_Anatomy_&_Physiology_attribution_5-0)** *This article incorporates [text](https://openstax.org/books/anatomy-and-physiology/pages/20-1-structure-and-function-of-blood-vessels) available under the [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/) license.* Betts, J Gordon; Desaix, Peter; Johnson, Eddie; Johnson, Jody E; Korol, Oksana; Kruse, Dean; Poe, Brandon; Wise, James; Womble, Mark D; Young, Kelly A (June 8, 2023). *Anatomy & Physiology*. Houston: OpenStax CNX. 20.1 Structure and function of blood vessels. [ISBN](/source/ISBN_(identifier)) [978-1-947172-04-3](https://en.wikipedia.org/wiki/Special:BookSources/978-1-947172-04-3).

## External links

- [Histology image: 66_02](http://www.ouhsc.edu/histology/Glass%20slides/66_02.jpg) at the University of Oklahoma Health Sciences Center – "Aorta"

- [Anatomy photo: Circulatory/vessels/vessels7/vessels2](https://web.archive.org/web/20081020010317/http://trc.ucdavis.edu/mjguinan/apc100/modules/Circulatory/vessels/vessels7/vessels2.html) - Comparative Organology at University of California, Davis — "Bird, vessels (LM, High)"

- [Image at About.com](http://biology.about.com/library/organs/heart/bltunica3.htm)

v t e Arteries and veins Vessels Arteries Nutrient artery Arteriole Metarteriole Elastic artery Capillaries Types Continuous Fenestrated Sinusoidal Precapillary sphincter Precapillary resistance Veins Vena comitans Superficial vein Deep vein Perforator vein Emissary veins Venous plexus Venule Lymph Lymphatic vessel Lymph Lymph capillary Circulatory system Systemic Left heart → Aorta → Arteries → Arterioles → Capillaries → Venules → Veins → Vena cava → (Right heart) Pulmonary Right heart → Pulmonary arteries → Lungs → Pulmonary vein → (Left heart) Microanatomy Microvessel Microcirculation Tunica intima Endothelium Internal elastic lamina Tunica media Tunica externa Vasa vasorum Vasa nervorum Vascular nerves Rete mirabile Circulatory anastomosis

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