Cui Dongmei. Atlas of Histology: with functional and clinical correlations. 1st ed

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Organ Systems

Circulatory System

Introduction and Key Concepts for the Circulatory System

The Cardiovascular System

Figure 9-1 Overview of the Cardiovascular System

Figure 9-2 The Heart and Its Impulse Conductive Function

Synopsis 9-1 Structure and Functions of the Heart

Figure 9-3A Layers of the Heart Wall: Endocardium, Ventricle

Figure 9-3B Layers of the Heart Wall: Myocardium, Ventricle

Figure 9-3C Layers of the Heart Wall: Epicardium, Ventricle

Figure 9-4A Purkinje Fibers and Intercalated Disks

Figure 9-4B Cardiac Valves

Figure 9-4C Clinical Correlation: Myocardial Infarction

Figure 9-5 A Representation of the General Structure of Blood Vessel Layers (Tunicae) and a

Comparison of the Medium Artery and the Medium Vein

Figure 9-6 A Representation of Types of Blood Vessels: Arteries, Veins, and Capillaries

The Arterial System

Figure 9-7A–C Large Arteries (Elastic Arteries)

Figure 9-8A–C Medium Arteries (Muscular Arteries)

Figure 9-9A Medium Artery

Figure 9-9B Small Artery

Figure 9-10A–C Small Arteries and Arterioles

Figure 9-11 Arteriole

Synopsis 9-2 Functions of Endothelium in Blood Vessels

Figure 9-12A Clinical Correlation: Coronary Artery Atherosclerosis

Figure 9-12B Clinical Correlation: Polyarteritis Nodosa (Vasculitis)

Synopsis 9-3 Pathological and Clinical Terms for the Circulatory System

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Organ Systems

The Capillary System

Figure 9-13A,B Continuous Capillaries

Figure 9-14A,B Fenestrated Capillaries

Figure 9-15A,B Discontinuous (Sinusoidal) Capillaries

The Venous System

Figure 9-16A–C Venules and Small Veins

Figure 9-17A–C Medium Veins

Figure 9-18A–C Large Veins

Table 9-1 Blood Vessels

The Lymphatic Vascular System

Figure 9-19A,B Lymphatic Vessels

Figure 9-19C Clinical Correlation: Lymphangioma

Introduction and Key Concepts

for the Circulatory System

The circulatory system includes the cardiovascular system

and the lymphatic vascular system. The cardiovascular system

includes the heart and the arterial, capillary, and venous sys-

tems. Blood is transported from the heart through the arterial

system to the capillaries, where exchange of gases, nutrients,

and other substances takes place. Blood is carried back to the

heart by the venous system. Blood ﬂ ows through two routes:

(1) The systemic circulation system transports oxygenated

blood from the heart to the capillaries in the tissues and

organs of the body and then collects and carries the blood

back to the heart (Fig. 9-1). (2) The pulmonary circulation

system transports deoxygenated blood from the heart to the

capillaries of the lungs. After gas exchange, blood is carried

back to the heart (see Fig. 9-1). The lymphatic vascular sys-

tem consists of lymphatic capillaries, lymphatic vessels, and

lymphatic ducts. This system collects lymph (excess tissue

ﬂ uid) from the tissues of all organs (except the nervous sys-

tem, bone marrow, and hard tissues) by lymphatic capillar-

ies and then transports it through lymphatic vessels to the

lymphatic ducts, which eventually empty the lymph into the

venous system. The collected lymph passes through lymph

organs, where it is ﬁ ltered, and lymphocytes are exposed to

antigens. Lymphopoiesis and the immune response occur here

(Fig. 9-19A,B).

The Cardiovascular System

The Heart

The heart contains four chambers: the left and right atria and

the left and right ventricles. The atria receive blood ﬂ ow dis-

charged from the venous system, whereas the ventricles pump

blood into the arterial system (Fig. 9-1). The wall of the heart

is composed of three layers: endocardium (innermost layer),

myocardium (middle layer), and epicardium (outermost layer).

(1) Endocardium consists of endothelium, subendothelial

connective tissue, and subendocardium (Purkinje ﬁ bers, small

coronary blood vessels, and nerve ﬁ bers). (2) Myocardium, the

thickest layer of the heart, contains an abundance of cardiac

muscle cells (Fig. 9-3A,B). Cardiac muscle contracts producing

heart beats, which are generated and regulated by the heart

conductive system including the sinoatrial (SA) node, the

atrioventricular (AV) node, the AV bundle, and Purkinje ﬁ bers

(Fig. 9-2). (3) Epicardium is covered by mesothelium and con-

tains ﬁ brous connective tissue, nerves, coronary vessels, and

adipose tissue (Fig. 9-3C).

Types of Blood Vessels

THE ARTERIAL SYSTEM is composed of large (conducting)

arteries, medium (distributing) arteries, small arteries, and arte-

rioles. The arterial system conducts blood (under higher pres-

sure than veins) from the ventricles to the capillary networks.

The walls of arteries can be generally divided into three layers:

tunica intima, tunica media, and tunica adventitia (Figs. 9-5

and 9-6).

Large arteries are also called elastic arteries because of the

large quantity of elastic material in their walls (Fig. 9-7A–C).

They have a thick tunica media with numerous elastic mem-

branes. The internal and external elastic laminae are hard to

distinguish from the nearby elastic membranes. Large arter-

ies conduct blood from the ventricles into the medium arter-

ies. Rich elastic materials in large arteries enable the vessels to

recoil to accommodate pressure changes and maintain a con-

tinuous ﬂ ow of blood during ventricular diastole (relaxation).

Medium arteries are also called muscular arteries because

of their thick tunica media, which contains circularly arranged

multiple layers of smooth muscle cells in a distinct sheath

(Figs. 9-8 to 9-9A). Internal and external elastic laminae are

easy to distinguish from nearby tissues.

Small arteries and arterioles are smaller diameter vessels.

The walls of small arteries contain two to six layers of smooth

muscle cells (Figs. 9-9B and 9-10A,B). Arterioles are the small-

est components of the arterial system, with only one or two

layers of smooth muscle cells (Figs. 9-10A,C, and 9-11). They

control the blood ﬂ ow into the capillaries.

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157

THE CAPILLARY SYSTEM contains continuous capillaries,

which have a continuous basal lamina and complete endothe-

lial cells. These structures allow only a very limited amount of

materials to pass through the capillary walls (Fig. 9-13A,B).

Fenestrated capillaries have a continuous basal lamina

and fenestrated endothelial cells (perforated by small pores).

A greater range of substances can, therefore, pass through the

capillary walls (Fig. 9-14A,B).

Discontinuous (sinusoidal) capillaries have a discontinuous

(or missing) basal lamina and incomplete endothelial cells

(perforated by large pores), which allow proteins and other

materials, even cells, to pass through the capillary walls freely

(Fig. 9-15A,B).

THE VENOUS SYSTEM is composed of venules and small,

medium, and large veins. Veins collect blood (under lower pres-

sure than arteries) from capillaries and transport it to the heart.

Veins have larger, ﬂ at lumens and thinner walls than their com-

panion arteries (Figs. 9-5 and 9-6).

Venules and small veins have very thin walls and few valves.

Venules drain exchanged blood from the capillaries to the small

veins. Venules are the primary sites of many inﬂ ammatory

reactions (Fig. 9-16A–C).

Medium veins have various diameters, and their structure

varies based on their size and location. Segments of medium

veins in some locations have a thick tunica adventitia with a

few longitudinal smooth muscle bundles (Fig. 9-17A–C). Valves

are prominent in medium veins, with an abundance in the

extremities to prevent blood from ﬂ owing backwards.

Large veins have a thick tunica adventitia with numerous

longitudinal smooth muscle bundles, which help to force blood

to ﬂ ow toward the heart (Fig. 9-18A–C). There are some large

valves in the large veins.

The Lymphatic Vascular

System

Lymphatic Vessels

The lymphatic vessels have a structure similar to small veins

(Fig. 9-19A,B). They have a large lumen, and valves are plenti-

ful in all sizes of lymphatic vessels.

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Organ Systems

T. Yang

Large veins (vena cava)

Large (pulmonary) veins

Large arteries (pulmonary artery)

Large arteries

Aorta

Arterioles

Small arteries

: right atrium

: left atrium

: right ventricle

: left ventricle

edium

arteries

Medium

arteries

Pulmonary circulation

Systemic circulation

Medium veins

Small veins

Venules

Deoxygenated blood in pulmonary circulation system

Oxygenated blood in pulmonary circulation system

Oxygenated blood in systemic circulation system

Deoxygenated blood in systemic circulation system

Systemic circulation system

Organs and tissues of the body

Lungs

Pulmonary

capillaries

Systemic

capillaries

Pulmonary circulation system

Left

ventricle

Right

ventricle

Small arteries

Arterioles

Venules

Small

veins

Small

veins

Medium

veins

Medium

veins

Large veins

(vena cava, etc.)

Large veins

(pulmonary veins)

Right

atrium

Left

atrium

Systemic capillaries

(exchange of gases

and other substances)

Pulmonary capillaries

(gas exchange)

Large/elastic arteries

(aorta, etc.)

Large/elastic arteries

(pulmonary arteries)

Medium systemic

arteries (muscular arteries)

Medium pulmonary

arteries (muscular arteries)

Pulmonary circulation system

Systemic circulation system

Figure 9-1. Overview of the cardiovascular system.

The cardiovascular system consists of the heart, arterial system, venous system, and capillary system. The heart is composed of two

atria and two ventricles. The right atrium receives blood from the body, and the left atrium receives blood from the lungs; the left

ventricle pumps blood to the body, and the right ventricle pumps blood to the lungs. The arterial system conducts blood from the

heart to capillaries in the body and the lungs. This system includes large arteries (elastic arteries), medium arteries (muscular arter-

ies), small arteries, and arterioles. The venous system carries blood from the capillary system in the body and lungs to the heart.

It includes venules, small veins, medium veins, and large veins. The capillary system is located between arterioles and venules and

often forms capillary beds where exchange of gases and various substances and movement of blood cells (diapedesis) take place. It

includes continuous, fenestrated, and sinusoidal (discontinuous) capillaries. Blood ﬂ ows through two routes: (1) the systemic circu-

lation system, which supplies oxygenated blood from the heart to the organs and tissues of the body and then carries deoxygenated

blood back to the heart and (2) the pulmonary circulation system, which sends deoxygenated blood from the heart to the lungs for

gas exchange and then returns oxygenated blood to the heart.

Systemic and Pulmonary Circulation Systems

The Cardiovascular System

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159

SYNOPSIS 9-1 Structure and Functions of the Heart

The heart is composed of two ■ atria (singular: atrium) and two ventricles.

The wall of the heart consists of

■ endocardium (inner layer), myocardium (cardiac muscle layer), and epicardium (outer

layer).

Endocardium

■ is composed of endothelium, subendothelium (a thin layer of connective tissue), and subendocardium.

Purkinje ﬁ bers are located in the subendocardium.

Myocardium

■ is composed of cardiac muscles, the thickest layer of the heart; cardiac muscles are branched and connected

to each other end to end by intercalated disks (junction complexes). Cardiac muscle ﬁ bers require high oxygen supply.

Epicardium

■ is composed of mesothelium and a thicker layer of connective tissue, which contains coronary vessels, nerves,

and adipose tissue.

The

■ conductive system of the heart consists of groups of specially modiﬁ ed cardiac muscle ﬁ bers, the SA node, AV node,

AV bundle, and Purkinje ﬁ bers.

Figure 9-2. The heart and its impulse conductive function.

The contractions of the right and left atria and ventricles must be coordinated precisely in order for blood to be pumped efﬁ ciently to

the lungs for oxygenation and then to the rest of the body. A network of specially modiﬁ ed cardiac muscle ﬁ bers generates and con-

ducts electrical impulses that provide the necessary coordination. This network includes the SA node, the AV node, the AV bundle,

and Purkinje ﬁ bers. (1) The SA node is located in the right atrial wall near the opening of the superior vena cava. The SA node is

important for initiating the heartbeat impulse and controlling its frequency; it is also called the “pacemaker” of the heart. (2) The AV

node is also located in the right atrial wall, medial to the right AV valve, and along the lower part of the interatrial septum. (3) The

AV bundle arises from the AV node and divides into two branches (right and left) to run along the sides of the interventricular sep-

tum. (4) Purkinje ﬁ bers are the terminal branches of the right and left branches of the AV bundle. Purkinje ﬁ bers run along the infe-

rior and lateral wall of the ventricle and extend to the papillary muscles. These ﬁ bers are modiﬁ ed large cardiac muscle cells, which

contain numerous gap junctions and well-developed intercalated disks. The SA node generates the heartbeat signal, which quickly

spreads to adjacent cardiac muscle cells in the myocardium of both atria to cause the atria to contract. Impulses are also picked up

by the AV node and travel along the AV bundle. These impulses pass through the right and left bundle branches to Purkinje ﬁ bers

in the ventricles, where they induce contraction of the cardiac muscles of the ventricles. There is a time delay, which allows the atria

to contract ﬁ rst to empty blood into the ventricles, before the ventricles contract. This time delay ensures that blood ﬂ ows smoothly

from the atria to the ventricles and then to the conductive arteries.

Superior

vena cava

Inferior

vena cava

Sinoatrial (SA)

node

Atrioventricular

(AV) node

Atrioventricular

(AV) bundle

Left bundle branch

Purkinje fibers

Left pulmonary veins

Right bundle

branch

Papillary

muscle

Cardiac

valves

RV:

LV:

right ventricle

left ventricle

Left

atrium

Right

atrium

Myocardium

Epicardium

Endocardium

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Organ Systems

Myocardium

Endocardium

Myocardium

Figure 9-3A. Layers of the heart wall: endocardium, ventri-

cle. H&E, 68

The wall of the heart is much thicker than the wall of the large

vessels and is composed of three basic layers, as are the blood

vessels: endocardium (equivalent to the tunica intima), myocar-

dium (equivalent to the tunica media), and epicardium (equiva-

lent to the tunica adventitia). The endocardium is the innermost

layer of the heart wall, which lines the lumen of the heart. This

layer consists of endothelium (simple squamous epithelium),

subendothelial connective tissue, and subendocardium. The

subendocardium is in contact with the cardiac muscle and con-

tains small coronary blood vessels, nerves, and Purkinje ﬁ bers

in certain areas (Fig. 9-4A). Some adipose cells are also pres-

ent within the connective tissue. The endocardium provides a

smooth lining for the four chambers of the heart and provides a

covering for the AV valves.

Nuclei of the cardiac muscle cells

Branched

cardiac muscle

Branched

cardiac muscle

Intercalated disk

Figure 9-3B. Layers of the heart wall: myocardium, ventri-

cle. H&E, 272; insets 786

Myocardium is the thickest layer of the heart wall and makes up

the bulk of the heart. It consists of cardiac muscle cells that are

arranged in branching columns. The ends of the cardiac mus-

cle cells are connected to each other by intercalated disks. The

inset shows cardiac muscles with their characteristic striations

and an intercalated disk (Fig. 9-4A). These muscles contract

to pump blood out of the ventricles of the heart and distribute

blood to the tissues and organs of the body. Myocardium of the

left ventricle wall is the thickest because of the fact that it must

pump the blood a great distance and overcome the high pressure

and resistance of the systemic circulation. In general, the atria

have thinner walls than the ventricles. Myocardium of the right

atrium is the thinnest because of the relatively low pressure and

resistance of the blood circulation.

Epicardium

(visceral layer)

Myocardium

Epicardium

(visceral layer)

Myocardium

Lumens of the

blood vessels

Figure 9-3C. Layers of the heart wall: epicardium, ventricle.

H&E, 68

Epicardium surrounds the heart. It is a layer of connective tissue

that contains nerves, blood vessels, and adipocytes. The inner

surface of the epicardium is connected with cardiac muscle, and

the outer surface is covered by mesothelium (see Fig. 3-2) that

faces the pericardial cavity. Mesothelium secretes a ﬂ uid known

as pericardial ﬂ uid, which provides lubrication and reduces fric-

tion between the epicardium (visceral pericardium) and the pari-

etal pericardium during the movements caused by heart contrac-

tion. Epicardium covers and protects the heart and allows small

blood vessels and nerves to pass through to provide nutrients

and nerve innervation.

Pericardial effusion refers to excess ﬂ uid in the pericardial

cavity due to inﬂ ammation of the pericardium (pericarditis);

hemopericardium is a condition in which blood is trapped in

the pericardial cavity. In either case, compression of the thin-

walled atria and vena cava can result in cardiac tamponade

and failure of circulation.

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161

Figure 9-4C.

Myocardial Infarction. H&E, 68

Myocardial infarction (MI), also known as a heart attack, occurs

when the blood supply to part of the heart is completely or partially

blocked because of atherosclerosis or the rupture of an atheroscle-

rotic plaque and the formation of a blood clot. Symptoms range from

characteristic chest discomfort (angina) and shortness of breath to

sudden death. Coronary artery disease (CAD) is the most common

underlying cause of this medical emergency. Atherosclerotic plaques,

which consist of lipids, ﬁ broblasts, collagen, and white blood cells

(especially macrophages), are found in the wall of an affected cor-

onary artery. The plaques cause luminal narrowing or occlusion

(Fig. 9-12A). The histologic appearance of MI depends on the age

of the infarct. Early changes include edema and hypereosinophilia,

followed by inﬁ ltration by neutrophils, coagulation necrosis, phago-

cytosis of dead cells by macrophages, formation of granulation tis-

sue, and, ultimately, the formation of a dense collagenous scar.

Necrotic

cardiac muscle

Remaining

normal cardiac

muscle cells

Spongiosa

Endothelium

Papillary

muscle

Mitral valves

Tricuspid

valve

Chordae

tendineae

Endothelium

Fibrosa

Ventricularis

Figure 9-4B. Cardiac valves, aortic valve. H&E, 134

There are four valves in the heart: two AV valves (mitral and tricuspid

valves) in the chambers and two semilunar valves (aortic and pul-

monary valves) in the arteries leaving the heart. Heart valves consist

of connective tissues and both surfaces are covered by endothelium.

They are composed of three layers: (1) Spongiosa consists of loosely

arranged collagen and elastic ﬁ bers and the surface is covered by the

endothelium. This layer is continuous with the atrial or blood vessel

side. (2) Fibrosa is the core of the heart valve, which contains dense

irregular connective tissue. (3) Ventricularis is a dense connective tis-

sue layer with many elastic and collagen ﬁ bers. The surface of the

ventricularis is covered by endothelium. The heart valves open and

close to allow the blood to ﬂ ow through the openings and to prevent

the backﬂ ow of blood. Shown is an example of the aortic valve. The

aortic valve has three cusps and lies between the left ventricle and the

aorta. The tricuspid and mitral valves are anchored to the ventricle

wall by chordae tendineae, which are attached to papillary muscles.

Common heart valve diseases include calciﬁ c aortic valve disease,

valvitis, and rheumatic heart disease. These diseases can lead to aortic

stenosis, aortic regurgitation, embolism, and mitral valve stenosis.

Figure 9-4A. Purkinje ﬁ bers and intercalated disks, ventricle.

H&E, 136; inset (right) 198, inset (left) 229

Purkinje ﬁ bers (impulse-conducting ﬁ bers) are large, modiﬁ ed car-

diac muscle cells, which are part of the heart conducting system. They

are terminal branches of the AV bundle branches (Fig. 9-2), located in

subendocardial connective tissue. Purkinje ﬁ bers often appear large in

size and cluster as groups. Each cell has only one or two nuclei and pale-

staining cytoplasm because it has fewer myoﬁ brils than regular cardiac

muscle cells. Purkinje ﬁ bers work together with other impulse- conducting

structures to regulate the heartbeats by conveying impulses to neigh-

boring cardiac muscle cells (Fig. 9-2). Intercalated disks are specialized

junctional complexes that contain fascia adherens, desmosomes (macula

adherens), and gap junctions, which provide connection and communi-

cation between the cardiac muscle cells. Intercalated disks bind cardiac

muscle cells together in an entire unit to prevent muscle cells being pulled

apart during contraction. They also provide ion exchange through gap

junctions, allowing electrical impulses to pass from one cell to another.

Nuclei of

muscle cells

Intercalated

disk

Purkinje

fibers

Purkinje fibers

Subendocardial

connective

tissue

Cardiac muscle

(cross section)

Purkinje

fibers

Purkinje fibersPurkinje fibers

Subendocardial

connective

tissue

Cardiac muscle

(cross section)

Cardiac muscle

(longitudinal section)

Cardiac muscle

(longitudinal section)

Intercalated

disk

Nuclei of

muscle cells

Myocardium

Endocardium

CLINICAL CORRELATIONS

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Organ Systems

Figure 9-5. A representation of the general structure of blood vessel layers (tunicae) and a comparison of the medium artery and

the medium vein.

The walls of the blood vessels can be divided into three layers (tunicae). The innermost layer in contact with the blood is called the

tunica intima. This layer contains endothelium and subendothelial connective tissue and may contain an internal elastic lamina (IEL)

in some vessels, particularly arteries. The endothelium is a layer of simple squamous cells, which forms the smooth surface of the

lumen. Subendothelial connective tissue is a thin layer of connective tissue beneath the endothelium. The IEL, if present, is a sheet

of elastic material that divides the tunica intima from the tunica media. The middle layer is called the tunica media. It primarily

contains circularly arranged smooth muscle cells (except in elastic arteries). Contraction and relaxation of these smooth muscle cells

will change the vessel diameter and affect blood pressure. The outermost layer, the tunica adventitia, is a layer of connective tissue

dominated by collagenous and elastic ﬁ bers. In large and some medium veins, the tunica adventitia may also contain longitudinal

smooth muscle bundles. Tunica adventitia surrounds and covers the vessels for protection. Occasionally, small blood vessels called

vasa vasorum are found in the tunica adventitia of large vessels. The vasa vasorum provide oxygen and nutrients for the large vessel

walls when the distance from the lumen is great and it is difﬁ cult to get nutrients from diffusion. Some differences between a medium

artery and a medium vein are listed here: (1) the artery has a smaller and more rounded lumen, whereas the vein has a larger and

oval or irregular-shaped lumen; (2) the artery has a thicker wall than does the vein; (3) in the artery, the tunica media is much thicker

than the tunica adventitia, but in the vein, the tunica adventitia is much thicker than the tunica media; (4) circularly oriented smooth

muscle cells form uniform sheets in the tunica media of the artery; however, smooth muscle cells are fewer and do not form a distinct

sheet in the vein; (5) There are a few longitudinal smooth muscle bundles in the tunica adventitia of medium veins in some locations,

whereas these smooth muscle bundles are more abundant in large veins. This pattern does not occur in arteries. Longitudinal smooth

muscle bundles in the tunica adventitia of the vein contract to help push blood back to the heart; and (6) valves are present in many

veins, especially in the medium veins of the extremities. Their function is to prevent gravitational backﬂ ow of the blood and to help

blood return to the heart. Arteries do not have valves (except the aortic and pulmonary valves).

Fibroblast

Tunica

adventitia

Tunica

adventitia

Tunica

media

Tunica

media

Tunica

intima

Tunica

intima

External elastic

lamina ( )EEL

Internal elastic

lamina ( )IEL

Connective

tissue

Connective

tissue

smooth muscle

with connective

tissue

Circular

smooth muscle

Circular

Longitudinal

smooth

muscle

Endothelial cells

Subendothelial

layer

Subendothelial

layer

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163

Figure 9-6. A representation of types of blood vessels: arteries, veins, and capillaries.

Blood vessels make up the arterial, the venous, and the capillary systems. In general, arteries have smaller, rounder lumens than

veins; their tunica media are thicker than the tunica adventitia, and the IEL are prominent. Veins have larger, ﬂ atter lumens than

arteries; longitudinal smooth muscle bundles may be present in the tunica adventitia, which is the most dominant layer in large

and some medium veins. The tunica adventitia is much thicker in the veins than the tunica media. For details, also see Table 9-1.

Exchange of gases, nutrients, and materials occurs in the capillaries. Three types of capillaries are illustrated here. Continuous cap-

illaries have complete endothelial cells and continuous basal laminae. Fenestrated capillaries have continuous basal laminae with

fenestrated endothelial cells (perforated by small pores); discontinuous (sinusoidal) capillaries have incomplete endothelial cells

perforated by large pores, and part of the cytoplasm may be missing. The basal lamina is discontinuous. Discontinuous capillaries

have gaps between endothelial cells, and their lumen sizes are much larger than the other two types. Blood vessel sizes are not drawn

to scale.

D. Cui /T. Yang

T. Yang

Large artery

(elastic artery)

Large vein

Medium artery

(muscular artery)

Medium vein

Small artery

Small vein

Arteriole

Venule

Continuous capillary

Fenestrated capillary

Discontinuous (sinusoidal)

capillary

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The Arterial System

Figure 9-7A. A representation of a large (elastic) artery.

Large arteries (elastic arteries) are also referred to as

conducting arteries, because of their function in conduct-

ing blood ﬂ ow out of the heart. There are abundant elastic

laminae (thick bundles of elastic ﬁ bers) in the tunica media

of large arteries, which enable the walls to recoil to resist

pressure as well as to maintain arterial pressure during

diastole when the ventricles are relaxed and pressure is not

generated by the heart. Small vessels located in the tunica

adventitia are called vasa vasorum; they supply the tissue

of the artery wall with oxygen and nutrients when they are

far from the lumen and diffusion of nutrients is difﬁ cult.

The aorta, pulmonary arteries, and their main branches

are good examples of elastic arteries.

D. Cui /T. Yang

Vasa vasorum

Nerve

Fibroblast

Elastic lamina

Connective tissue

Smooth

muscle cell

Endothelial cell

Tunica

adventitia

Tunica

media

Tunica

intima

Elastic

laminae

Tunica

adventitia

Tunica

media

Tunica

intima

Elastic

laminae

Tunica

adventitia

Tunica

media

Tunica

intima

Figure 9-7B. Large (elastic) artery, carotid artery. Elastic

stain, 68; inset 242

This is an example of a large artery (elastic artery) from a

portion of the carotid artery. The carotid artery generally

has the characteristics of elastic arteries. The tunica media

of the vessel wall has multiple layers of elastic lamina that

are well organized in concentric fashion. These elastic

laminae are sheets of fenestrated elastic material produced

by smooth muscle cells in the tunica media. These cells are

interspersed between the elastic laminae (see Fig. 4-9B).

The elastic laminae in this specimen are revealed as par-

allel wavy black sheets by a special elastic stain; smooth

muscle cells are not visible here with this type of stain. The

tunica adventitia of an elastic artery consists of loosely

arranged connective tissue ﬁ bers. These ﬁ bers are mainly

collagen ﬁ bers, with a small number of elastic ﬁ bers that

are produced by ﬁ broblasts.

Tunica

adventitia

Tunica

media

Vasa

vasorum

Smooth

muscle cells

Elastic

laminae

Tunica

adventitia

Tunica

media

Tunica

intima

Smooth

muscle cells

Elastic

laminae

Figure 9-7C. Large (elastic) artery, aorta. H&E, 68;

insets 198

An example of a large artery (aorta) is shown. The elastic

laminae are pink and are more difﬁ cult to distinguish with

routine H&E stain than they are with elastic stains. The

dark nuclei in the tunica media belong to smooth muscle

cells (left inset), which produce the elastic membrane.

There are some vasa vasorum deep in the tunica adven-

titia (right inset), which provide oxygen and nutrients for

the tunica media and tunica adventitia of the large artery

wall. Nerves belonging to the autonomic nervous system

may occasionally be found in the tunica adventitia (see

Fig. 9-7A).

CUI_Chap09.indd 164 6/17/2010 10:22:40 AM