HM Practical - Blood Vessel Histology

Embryology - 11 Dec 2023 Expand to Translate
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Introduction

Adult human cardiovascular system

Historic drawing of a small artery and vein.

HMA Practical 3 for Monday July 23 and Wednesday July 25.

HMA Practical 3 Virtual Slides

This page provides histology support information for blood vessel structure.

Disclaimers

does not form part of the actual practical class based upon the virtual slides.
does not cover the pathology content.
does not cover lymphatic vessels, they are covered in the SH lymphatic practical.

Aims

To understand the microscopic appearance of normal blood vessels of different dimensions and to recognize changes in the arterial wall as seen in atherosclerosis.

Key concepts

Normal structure of large and medium blood vessels; tunica intima, tunica media & tunica adventitia and capillaries.
Relation of blood vessel structure to function.
Abnormalities of arteries in atherosclerosis.

Practical class activities

Note the features listed for the following virtual slides linked from: http://vslides.unsw.edu.au

Aorta (elastic artery) - (2 virtual slides) Showing layers of the wall: tunica intima, tunica media and tunica adventitia. The media is extensive with multiple layers of smooth muscle mixed with elastic laminae, some of which are fenestrated. Vasa vasorum and nervi vasorum in the tunica adventitia; capillaries in adipose tissue surrounding the artery. (Note: capillaries are roughly 8 micrometers in diameter, enough to see 1 or 2 red blood cells inside the lumen).
Medium sized (muscular) artery and vein - (2 virtual slides) Distinct layers of wall of an artery: tunica intima, internal elastic lamina, tunica media (many layers of smooth muscle), external elastic lamina (multiple layers) extending into tunica adventitia; In the vein, the same 3 tunics can be seen but the tunica media is reduced, and the tunica adventitia is wider compared to the artery.
Vena cava - Showing the 3 layers with an extensive tunica adventitia. Special features are the longitudinal smooth muscle bundles in the tunica adventitia.
Atherosclerosis, artery - (Pathology is not covered on this histology support page) This section of a muscular artery from a 60-year-old male is very different from the normal vessels that you have just looked at. An adaptive tutorial is available to assist you to identify the features in this section.

Flow

Starting at the Heart:

Elastic arteries (conducting) - large arteries
- examples - aorta, brachiocephalic, common carotid, subclavian, vertebral, common iliac arteries.
- thin wall compared to diameter.
- tunica media more elastic fibres, less smooth muscle.
- pressure reservoir.
Muscular arteries (distributing) - medium sized arteries
- examples - axillary, brachial, radial, intercostal, splenic, mesenteric, femoral, popliteal, tibial.
- capable of greater vasoconstriction/vasodilation.
- adjust blood flow rate.
Arterioles - small arteries deliver blood to capillaries.
- tunica interna, media (smooth muscle few elastic fibres), externa (elastic and collagen fibres)
- regulate blod flow into capillaries.
Capillaries - smallest vessels.
- endothelium and basement membrane.
- main site of exchange (nutrients, waste).
- connect arterioles and venules.
Venules - smallest veins.
- uniting capillaries drain into veins.
- further from capillary bed tunica media increases.
Veins - same 3 coats as arteries.
- tunica interna and tunica media thinner than companion artery, tunica externa thicker.
- many veins contain valves to prevent back flow.

Aorta

Blood vessel wall

tunica intima

delimits the vessel wall towards the lumen of the vessel and comprises its endothelial lining (typically simple, squamous) and associated connective tissue.
Endothelium - simple squamous epithelium, cells organised longitudinally, joined by tight and gap junctions.
Internal elastic lamina (layer, membrane) not obvious due to may elastic layers.
the tunica intima of elastic arteries is thicker than in other arteries.

tunica media

layer of circumferential smooth muscle and variable amounts of connective tissue.
A second layer of elastic fibers, the external elastic lamina, is located beneath the smooth muscle.
Components
- Elastin - fenestrated sheets or lamellae between muscle layers.
- Smooth Muscle Cells - arranged in layers.
- Collagen fibre and ground substance.

tunica adventitia

mainly of connective tissue fibres.
The tunica adventitia blends with the connective tissue surrounding the vessel, and the definition of the outer limit of the tunica adventitia is therefore somewhat arbitrary.
Thin - collagen fibres, elastic fibres (not lamellae), fibroblasts, macrophages.
vasa vasorum - (Latin, "vessels of the vessels") the network of small blood vessels that supply large blood vessels.

Labeled


Aorta overview	Aorta elastin

Unlabeled

Aorta overview
Aorta elastin

Arteries

elastic arteries - the tunica intima of elastic arteries is thicker than in other arteries.
muscular arteries
arterioles - smaller vessels with a diameter below 0.1 - 0.5 mm. Endothelial cells are smaller than in larger arteries, and the nucleus and surrounding cytoplasm may 'bulge' slightly into the lumen of the arteriole. Endothelium rests on a internal elastic lamina, which may also be incomplete. The tunica media consists of 1-3 concentric layers of smooth muscle cells. Difficult to identify an external elastic lamina or to distinguish the tunica adventitia from the connective tissue surrounding the vessel. Smooth muscle regulates tissue blood flow and arterioles receive both sympathetic and parasympathetic innervation.
capillary - arise from the final branches of arterioles, lined by a endothelial cells, each cell forms the wall around the entire circumference of a segment of the capillary. The lumen only allows 1-2 red blood cells to fit side by side in the capillary. Three main types of capillaries (continuous, fenestrated and discontinuous) can be distinguished based on features of their endothelium.

Muscular Arteries

Medium sized (muscular) artery and vein - (2 virtual slides)
Distinct layers of wall of an artery: tunica intima, internal elastic lamina, tunica media (many layers of smooth muscle), external elastic lamina (multiple layers) extending into tunica adventitia;

Neurovascular bundle
In the vein, the same 3 tunics can be seen but the tunica media is reduced, and the tunica adventitia is wider compared to the artery.
nervi vasorum - (nervi vascularorum) vascular nerves that innervate both arteries and veins and control vessel vasodilation and vasoconstriction.
- The toluidine blue stains nucleic acids blue and polysaccharides purple and also increases the sharpness of histology slide images.


Artery overview	Artery detail

Artery elastin	Artery elastin detail

Unlabeled

Artery overview
Artery elastin
Artery tunica media elastin
Artery elastin detail

Capillaries

Electron Micrographs

Vascular Sinus EM1

‎‎Mobile | Desktop | Original

EM Slides

Capillary EM1

‎‎Mobile | Desktop | Original

EM Slides

Capillary 1 large labeled
Capillary 1 large unlabelled
Capillary 1 small labeled
Capillary 1 small unlabelled
endothelium detail
Containing white blood cell

Vena cava

Valves are absent.

tunica intima - contains some subendothelial connective tissue.
tunica media - comparatively thin with collagen and elastic fibres.
tunica adventitia - very wide, contains bundles of longitudinal smooth muscle and the transition to the surrounding connective tissue is gradual.

Vein

Vein valve

Small to medium-sized veins are characterised by the presence of valves.

Animation shows how venous valves prevent the back flow of blood.

valves are formed by loose, pocket-shaped folds of the tunica intima.
one to three pockets form the valve.
Valves are absent in largest veins of the abdomen and thorax.

Venule with endothelium (simple squamous epithelium) lining. (Stain - Haematoxylin Eosin)

Note the obvious difference between this small venule and a capillary is the increased lumen size.

Terms

artifact - changes and distortions introduced to the normal tissue structure by the histological processing. Common artifacts include: folds (gives the tissue a darker appearance), tears (rips in the tissue can be seen in epithelia), shrinkage when tissues loose mainly liquid through histological processing, and cuts often used in tissue preparation.
elastic fibres - coloured light yellow in fresh tissues, special stains required to show in tissue sections. Composed of the protein elastin, can be stretched and return to original length.
elastic laminae - layer of elastic tissue in a blood vessel wall.
external elastic lamina - elastic tissue layer that lies within the tunica media of blood vessels.
internal elastic lamina - (internal elastic lamella) elastic tissue layer that forms the outermost part of the tunica intima of blood vessels.
nervi vasorum - (nervi vascularorum) vascular nerves that innervate both arteries and veins and control vessel vasodilation and vasoconstriction.
pericyte - (Rouget cells, mural cells) a contractile cell located around endothelial cells of capillaries, venules and larger lymphatic vessels. Role in regulating blood flow, phagocytosis, and signalling.
tunica - (Latin, "tunic") refers to a coat or coating surrounding a blood vessel.
tunica adventitia - (adventitia, tunica externa) the outermost layer of a blood vessel surrounding the tunica media. Anchors blood vessel to surrounding tissue and consists of many collagen fibres.
tunica intima - (intima) innermost layer in both arteries and veins.
tunica media - (media) middle layer in both arteries and veins.
vasa vasorum - (Latin, "vessels of the vessels") the network of small blood vessels that supply large blood vessels.
vena cava - the largest veins in the body, formed by the superior vena cava (SVC) and inferior vena cava (IVC).

Search Pubmed: Atherosclerosis | Atherosclerosis images

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Cite this page: Hill, M.A. (2023, December 11) Embryology HM Practical - Blood Vessel Histology. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/HM_Practical_-_Blood_Vessel_Histology

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