Tunica intima

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Tunica intima
Blausen 0055 ArteryWallStructure.png
Gray448.png
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 ofWall 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

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

Contents

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. [3]

Elastic arteries – A single layer of endothelial and a supporting layer of elastin-rich collagen. The layer also contains fibroblasts, immune cells and smooth muscle cells. [1]

Muscular arteries Endothelial cells

Arterioles – A single layer of endothelial cells

Veins Endothelial cells [3]

The inner coat consists of:

  1. 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.
  2. 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 ]
  3. An elastic or fenestrated 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 endothelins which are powerful vasoconstrictors. [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, and its overexpression can contribute to hypertension and cardiovascular disease. [5]

Additional images

Related Research Articles

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The aorta is the main and largest artery in the human body, originating from the left ventricle of the heart, branching upwards immediately after, and extending down to the abdomen, where it splits at the aortic bifurcation into two smaller arteries. The aorta distributes oxygenated blood to all parts of the body through the systemic circulation.

<span class="mw-page-title-main">Artery</span> Blood vessels that carry blood away from the heart

An artery is a blood vessel in humans and most other animals that takes oxygenated blood away from the heart in the systemic circulation to one or more parts of the body. Exceptions that carry deoxygenated blood are the pulmonary arteries in the pulmonary circulation that carry blood to the lungs for oxygenation, and the umbilical arteries in the fetal circulation that carry deoxygenated blood to the placenta. It consists of a multi-layered artery wall wrapped into a tube-shaped channel.

<span class="mw-page-title-main">Blood vessel</span> Tubular structure of circulatory system

Blood vessels are the structures of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away from the tissues. Blood vessels are needed to sustain life, because all of the body's tissues rely on their functionality.

<span class="mw-page-title-main">Vein</span> Blood vessels that carry blood towards the heart

Veins are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and fetal circulations which carry oxygenated blood to the heart. In the systemic circulation, arteries carry oxygenated blood away from the heart, and veins return deoxygenated blood to the heart, in the deep veins.

<span class="mw-page-title-main">Capillary</span> Smallest type of blood vessel

A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the site of the exchange of many substances from the surrounding interstitial fluid, and they convey blood from the smallest branches of the arteries (arterioles) to those of the veins (venules). Other substances which cross capillaries include water, oxygen, carbon dioxide, urea, glucose, uric acid, lactic acid and creatinine. Lymph capillaries connect with larger lymph vessels to drain lymphatic fluid collected in microcirculation.

<span class="mw-page-title-main">Circulatory system</span> Organ system for circulating blood in animals

The circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, that consists of the heart and blood vessels. The circulatory system has two divisions, a systemic circulation or circuit, and a pulmonary circulation or circuit. Some sources use the terms cardiovascular system and vascular system interchangeably with circulatory system.

<span class="mw-page-title-main">Thrombus</span> Blood clot

A thrombus, colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cross-linked fibrin protein. The substance making up a thrombus is sometimes called cruor. A thrombus is a healthy response to injury intended to stop and prevent further bleeding, but can be harmful in thrombosis, when a clot obstructs blood flow through a healthy blood vessel in the circulatory system.

<span class="mw-page-title-main">Endothelium</span> Layer of cells that line the inner surface of blood vessels

The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall. Endothelial cells form the barrier between vessels and tissue and control the flow of substances and fluid into and out of a tissue.

<span class="mw-page-title-main">Venule</span> Very small blood vessel in the microcirculation

A venule is a very small vein in the microcirculation that allows blood to return from the capillary beds to drain into the venous system via increasingly larger veins. Post-capillary venules are the smallest of the veins with a diameter of between 10 and 30 micrometres (μm). When the post-capillary venules increase in diameter to 50μm they can incorporate smooth muscle and are known as muscular venules. Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules. Many venules unite to form a vein.

<span class="mw-page-title-main">Atheroma</span> Accumulation of degenerative material in the inner layer of artery walls

An atheroma, or atheromatous plaque, is an abnormal accumulation of material in the inner layer of an arterial wall.

<span class="mw-page-title-main">Vasa vasorum</span> Network of small blood vessels

Vasa vasorum are small blood vessels that comprise a vascular network supplying the walls of large blood vessels, such as elastic arteries and large veins.

<span class="mw-page-title-main">Basement membrane</span> Thin fibrous layer between the cells and the adjacent connective tissue in animals

The basement membrane, also known as base membrane, is a thin, pliable sheet-like type of extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between epithelial tissues including mesothelium and endothelium, and the underlying connective tissue.

<span class="mw-page-title-main">Tunica media</span> Middle layer of blood vessel

The tunica media, or media for short, is the middle tunica (layer) of an artery or vein. It lies between the tunica intima on the inside and the tunica externa on the outside.

<span class="mw-page-title-main">Arterial dissections</span> Medical condition

An arterial dissection is a tear within the wall of an artery, which allows blood to separate the wall layers. There are several types. Usually, a tear is in an arterial wall, but a vein wall tear has been documented.

<span class="mw-page-title-main">Tunica externa</span> Outer layer of blood vessel

The tunica externa, also known as the tunica adventitia, 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.

An elastic artery is an artery with many collagen and elastin filaments in the tunica media, which gives it the ability to stretch in response to each pulse. This elasticity also gives rise to the Windkessel effect, which helps to maintain a relatively constant pressure in the arteries despite the pulsating nature of the blood flow. Elastic arteries include the largest arteries in the body, those closest to the heart. They give rise to medium-sized vessels known as distributing arteries.

A muscular artery is a medium-sized artery that draws blood from an elastic artery and branches into "resistance vessels" including small arteries and arterioles. Their walls contain larger number of smooth muscles, allowing them to contract and expand depending on peripheral blood demand.

<span class="mw-page-title-main">Internal elastic lamina</span> Layer of elastic tissue in blood vessels

The internal elastic lamina or internal elastic lamella is a layer of elastic tissue that forms the outermost part of the tunica intima of blood vessels. It separates tunica intima from tunica media.

In biology, a tunica is a layer, coat, sheath, or similar covering. The word came to English from the Neo-Latin of science and medicine. Its literal sense is about the same as that of the word tunic, with which it is cognate. In biology, one of its senses used to be the taxonomic name of a genus of plants, but the nomenclature has been revised and those plants are now included in the genus Petrorhagia.

<span class="mw-page-title-main">Anatomical terms of microanatomy</span> Anatomical terminology is used to describe microanatomical (or histological) structures

Anatomical terminology is used to describe microanatomical structures. This helps describe precisely the structure, layout and position of an object, and minimises ambiguity. An internationally accepted lexicon is Terminologia Histologica.

References

PD-icon.svgThis article incorporates text in the public domain from page 498 of the 20th edition of Gray's Anatomy (1918)

  1. 1 2 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". Canadian Journal of Cardiology. 39 (12): 1781–1794. doi:10.1016/j.cjca.2023.09.009. PMID   37716639.
  2. Scipione, Corey A.; Cybulsky, Myron I. (October 2022). "Early atherogenesis: new insights from new approaches". Current Opinion in Lipidology. 33 (5): 271–276. doi:10.1097/MOL.0000000000000843. ISSN   0957-9672. PMC   9594136 . PMID   35979994.
  3. 1 2 Steve, Paxton; Michelle, Peckham; Adele, Knibbs (2003). "The Leeds Histology Guide".
  4. Haryono, A; Ramadhiani, R; Ryanto, GRT; Emoto, N (16 May 2022). "Endothelin and the Cardiovascular System: The Long Journey and Where We Are Going". Biology. 11 (5): 759. doi: 10.3390/biology11050759 . PMC   9138590 . PMID   35625487.
  5. Creative Commons by small.svg  This article incorporates text available under the CC 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 vessles. ISBN   978-1-947172-04-3.