vascular histology

8/13/2019 Vascular Histology

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Vascular includes both blood and lymphatic systems.

Arteries are efferent vessels (going away) which become smaller as they branch and carry blood to the

tissues.Capillaries are the smallest blood vessels which serve as the interchange between blood and tissues

Veins are afferent vessels which become larger as they approach and return blood to the heart

Veins

Venule --> medium sized vein --> large vein

Arteries

Arteriole --> muscular artery --> elastic artery

Heart

Internal endocardium

Middle myocardium (cardiac muscle)

External epicardium

On a microscopic level, the heart consists of three layers (tunics):

Endocardium

The first layer (in contact with the lumen). There is a thin layer of endothelial cells. These are supported

by connective tissue with both elastin and collagen (strength).

Connecting the endocardial CT to the myocardial tissue is the subendocardial layer which contains veins,

nerves and perkinje fibres

MyocardiumIt is the thickest layer of the heart and is also known as cardiac muscle. It is comprised of cardiac muscle

cells arranged in layers. In between the muscle fibres there are both a rich supply of capillaries and also

delicate supporting connective tissue.

Vascular

Histology

Striations

Centrally located nucleus (single nuclei)

Branching

Intercalated discs (squiggly line): highly specialised attachment

which joins cardiac cells together and allows them to contract

rapidly as a single unit

Vascular HistologyWednesday, 28 March 2012

3:06 PM

Case Based Learning Page 1


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Connective Tissue

Epicardium

The heart is covered externally by a simple squamous epithelium (mesothelium, secretes pericardialfluid) which is supported by CT known as epicardium. The 'epicardium' is also the visceral layer of the

epicardium.

Pericardium

It encloses the heart and holds it in place: outer fibrous and inter serous pericardium

The outer fibrous pericardium is a dense irregular CT which protects and anchors the heart, enabling it

to beat effectively (prevents overstretching). The serous pericardium consists of a parietal (outer) layer,

pericardial cavity with pericardial fluid and a visceral layer (epicardium).

Tissues of the Vascular Wall

Maintenance of selectively permeability barrier

Maintenance of nonthrombogenic barrier (prevents clotting)

Modulation of blood flow

Regulation and modulation of immune responses (enables white blood cells to migrate out

of the blood vessel)

Hormonal synthesis & other metabolic activities

Modification of lipoproteins

Simple squamous endothelium

Involuntary control

Smooth muscle

Larger blood vessels have 3 basic structural components:



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Occurs in walls of all vessels larger than capillaries

Arranged helically in layers (wrapped around in concentric layers)

Components vary based on local environments (dependant on function)

Connective tissue

Intima

Has a subendothilial layer with loose CT and a few smooth muscle cells. Has holes to enable substances

to nourish cells in vessel

Media

Concentric layers of smooth muscle cells interspersed with elastic fibres. Arteries

Adventitia

Vaso Vasorum

They are vessels within the walls of vessels which allow perfusion of blood to the cells of the vessel.

More in veins than arteries because veins carry deoxygenated blood. Supply adventitia and outer media.

Elastic Arteries

Large diameter vessels with very thick walls. Generally found closer to the heart (high pressure). Insteadof having large amounts of smooth muscle cells the media is high in elastin content (concentric elastic

laminae). It is able to stretch during systole and recoil during diastole, reduces the fluctuations in BP.

Many vaso varosum in adventitia

Tunica intima, epithelium and CT; lining of BV

Tunica media; smooth muscle; varies diameter of BV lumen (blood pressure)

Tunica Adventitia; Dence CT; tough protective outer coating of BV



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Venules

Contain endothelial cells with basement membrane and also a few

smooth muscle cells

As the diameter of the venule increases, the amount of smooth

muscle increases

They drain the capillary network.

Small Veins

The smooth muscle cells form a more continuous layer and eventually a adventitia composed of

collagenous CT is developed.

Intima is a thin endothelium with little CT

Media has less muscle cells (than arteries) and if patchy in arrangement

No internal of external elastic laminae

Adventitia is the predominant layer

Larger Veins

vascular histology

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