histologyofcardiovascular-2009

Ahmad Aulia Jusuf, Histology FMUI

CARDIOVASCULAR SYSTEMA View From Histological Aspect

Ahmad Aulia Jusuf, MD, PhDDepartment of Histology Faculty of Medicine University of Indonesia

2009

INTRODUCTION

The ciculation system is composed of cardiovascular system and the lymphatic

vascular system. The cardiovascular system is to carry blood in both directions between

heart and the tissue. The lymphatic vascular system is to collect the lymph, the excess

extracellular tissue fluid and deliver it back into the cardiovascular system.

The blood from the heart is pumped out

into two separated circuits: the pulmonary

circuit which carries blood to and from

lungs and the systemic circuit which

distributes the blood to and from all of the

organ and tiussues of the body. The blood

from the heart will circulate into aorta, the

largest artery that continue draining into

the medium and small arteries.

The blood then enters the extracellular

tissue fluid to give the oxygen and nutrient

for the cells. Then the waste of metabolism

and carbondioxyde will be drained into the

small vein (venue), medium vein and large

veins. From the large vein the blood is

circulated back into the heart

Figure-1 An Overview of cardiovascular

system

Cardivascular System February 03, 2009

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THE BLOOD VESSEL

In general the structure of blood vessel is composed of 3 tunics or layers

1. The tunica intima

The most internal layer is composed of a single layer of flattened, squamous

endothelial cells. The other structures are the subendotelial loose connective tisue

and the internal elastic tunic

2. The tunica media

This medial layer is composed of concentric smooth muscle layer, elastic fibers,

type III collagen fibers and proteoglycan

3. The external elastic lamina

The external elastic lamina is more delicate than the internal elastic lamina and

separates the tunica media from overlaying tunica adventisia.

4. Tunica Adventisia

This layer covers the outside surface of blood vessel, and msotly composed of

type I collagen fibers. In this part the vasa vasorum, the small arteries that enter

the vessel walls to give the nutrient for the wall of blood vessel.

Figure-2 Structure of blood vessel


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ARTERY

Arteries are efferent vessels that transport blood away from the heart to the

capillary bed. They can be classify into 3 types

1. Large artery (elastic artery, conducting artery)

The arteries belongs to this type are aorta, inominate artery, carotic communis

artery, subclavia artery, iliac artery

The tunica intima of elastic artery contains an endothelium, supported by the

narrow layer of underlying connective tissue. The endothelial cxells contain

Weibel-Palade bodies, an membrane inclusion that have a dense matrix containg

glycoprotein von Willibrand factor. Thin laminae of elastic fiber, the internal

elstic lamina are also present. The tunica media consists of many fenestrated

Figure-3 The histological appearance of aorta


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lamellae of elastin fibers and a few amount of smooth muscle. The external elastic

laminae is also present in the tunica media. Tunica adeventisia is relatively thin,

composed of loose fibroelastic connective tissue. The tunica adventisia contains

the vasavasorum. Vasa Vasorum is the small blood vessel located in the wall of

large artery or medium artery that functions in supplying the nutrient and oxygen

to that tissue

The function of large artery is to drainage the blood to the medium artery, to keep

the systolic pressure in the constan condition and to avoid the flunctuation of

blood flow.

2. Medium artery (muscular artery, distributing artery)

Figure-4 The Medium artery

The example of this type are brachialis artery, ulnar artery, femoral artery,

poplitea artery, coronary artery, umbilical artery and arteries located in the brain

The tunica intima in muscular artery is thinner than in the elastic arteries. The

internal elastic laminae is prominent and displays an undulating surface. The

tunica media is composed predominantly of smooth muscle cells. The external

elastic lamina is identifiable in histological sections as several layers of thin


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elastic sheets. The tunica adventisia consist of elastic fibers, collagen fibers and a

ground substance composed mostly of dermatan sulfate and heparan sulfate.

The function of medium artery is to distribute the blood to the atrget organ or

tissue.

3. Small artery (Arteriol)

Figure-5 The small artery

The endothelium of tunica intima is supported by a thin subendothelium layer

consisting of type III collagen and a few elasticfibers embedded in ground

substance. An internal elastic lamina is absent in small and terminal arterioles.

The tunica media is composed of a single smooth muscle cell layer. The tunica

adventisia is scant and is represented by fibroelastic connective tissue.


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Small artery (arteriol) is one component of microvascular sistem. This system

consists of arteriole, metarteriole, capillary and venule.

Vasoconstriction of arteriole will increase the peripheral resistency, resulting in

the increasing of systemic blood pressure

4. Metarteriol

A metarteriol is an artery that supply blood to capillary beds. The smooth muscle

layer is not continuous but spaced apart. It is thought that this arrangement

permits these smooth muscle cells to function as a sphincter upon contraction,

thus controlling blood flow into the capillary bed.

Figure-6 The capillary bed

The blood vessel is controlled by sympathetic and parasympathetic nerve system. The

sympathetic nerve system through adrenalin stimulates vasoconstriction, while the

parasympathetic through the acetylcholine stimulatse the vasodilation of vessel.


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CAPILLARIES

The smallest blod vessels arising from the terminal ends of the arterioles which

form, by branching and anastomosing, a capillary bed (network) between the arterioles

and venules.

Capillary has the diameter about 7-12 micrometer. Capillaries are formed by a

single layer of squamous endothelial cells known as endothel that is lined by basal

membrane. Pericytesare located along the outside of the capillaries and small venules.

These cells are flatenned in shape and contain tropomyosin isomyosin and protein kinase

which are all related to contraction that regulate the blood flow.

Figure-7 The capillary

There are 3 types of capillary

1. Continuous capillaries

The contonuous capillaries have no interruptions (pore or fenestrated) in their

wall. This type of capillary is present in the muscle, nervous and connective

tissues

2. Fenestrated capillaries


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The fenestrated capillaries have pore or fenestrae in their wall. This type of

capillary is present in the pancreas, intestines, endocrine and kidney

3. Sinusoidal capilaries

The sinusoidal capillaries, also known as sinusoids, have irregular shape

which conform to the shape of the structure in which they are located. This

capillaries can be found in the hemopoeitic tissue such as bone marrow and

spleen, liver, cortex of adrenal and adenohipophysis.

VEINS

The vein is afferent vessel that collect and transport the blood back to the heart.

The veins is characterized into 3 types based on size : small, medium and large veins.

Like artery veins is also characterized into 3 types

Figure-8 The small (left side) and medium (right side) veins


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1. Small vein

The shape of small venule is irregular, while the arteriole is round. Tunica intima

of venule is lined by a single flattened cells known as andothelial cells.

2. Medium veins

The histological apperance of medium vein is similar to medium artery but the

medium vein has no internal elastic lamina

3. Large veins

The tunica intima of large vein is similar to medium vein except the large veins

have a thick subendothelial connective tissue layer.

Many medium veins have valves that function to prevent the back flow of blood . A

venous valve is composed of two leaflets each composed of a thin fold of the intima

jutting out from the wall into the lumen

Arteriovenous anastomoses

Terminal of most arteries end in capillary beds, which deliver their blood to

venules for the return back to the venous side of the cardiovascular system. In many part

of our body however the artery simpley joins with a venous channel, forming an

arteriovenous anastomoses (AVA). This shunt is useful in thermoregulation and found

abundant in the skin. This segmen is innervated with adrenergc and cholinergic nerves.

THE LYMPHATIC SYSTEM

The lymphatic vascular system is a series of vessels that remove excess tissue

fluid (lymph) from the interstitial tissue spaces and return it to the cardiovascular system.

Lympahtic vessel are found throughout the body except in the central nervous system and

few other ares including cartilage, bone, bone marrow, thymus, teeth, internal ear and

placenta.

The lymphatic system is an open system in that there is no pump and no

circulation of fluid. The lymphatic vascular system begins in the tissue of the body as

blind ended lymphatic capillaries. The excess fluid in the extracelluar space enters the

lymphatic capillaries . The lymphatic capillaries empty their contents into lymphatic

vessels which empty into successively larger vessels until one of the two lymphatic duct


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Figure-9 The lymphatic vessel

is reached. These two lymphatic duct are right lymphatic duct and thoracic duct. The

right lymphatic duct collects lymph from the upper right quadrant of body, while the

thoracic duct collect lymph from the remainder of the body. The right lymphatic duct

empties its contents into the venous system at the junction of right internal jugular and

subclavian vein while the thoracic duct empties its contents at the junction of the left

internal jugular and subclavian veins

The lymphatic capillaries are composed of a single layer of endothelial cells with

an incomplete basal lamina. The small and medium lymphatic vessels are characterized

by closely space valves. Large lymphatic vessels resemble small vein structurally , except

their lumen are larger and their wall thinner. The smooth muscles in the tunica media are

arranged in the regular manner.

HEART

The heart is the pump for the cardiovascular system. Its muscular wall

(myocardium) is composed of cardiac muscle. The heart consists of four chambers two

atria which receive the blood and two ventricles which discharge blood from the heart.

The wall of heart is composed by 3 layers that are homologous to the tunica

intima, tunica media, and tunica adventitia respectively in the blood vessels. They are

1. Endocardium that lining the heart lumen and direct contact to the blood

2. myocardium, located in the middle part that contains the cardiac muscle cells


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3. epicardium, also called as visceral layer of pericardium that covers the

myocardium

Figure- 10 the layers of heart

Endocardium

The endocardium will continuous with the tunica intima of the blood vessel entering and

leaving the heart. The endocardium is made up of

1. An endothelium composed of simple squamous epithelium

2. Subendothelium which contains the collagenous and elastic fibers

3. Subendocardium, a layer which is consists of loose connective tissue. The

subendocardium of ventricle and interventricular septum contain the Purkinje

fibers, the modified myocardium that functions in nerve conducting system. The

subendocardium layer is absent in the papilaris muscle and corda tendinae.


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Figure-11 Endocardium

Figure-12 The Purkinje fibers in subendocardium

Myocardium

Myocardium contains the cardiac muscle cells, which are arranged in complex

spirals around the orifices of chambers. The cardiac muscle consists of separate cellular

units and is uni\nucleate. Furthermore cardiac muscle is characterized by rhythmic,

involuntary contractions controlled by autonomic innervation.


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The cardiac muscle cells have 3 specialized properties. They are contraction,

endocrine secretion and impulse generation or impulse conduction.

The specialized cardiac muscle cells located primarily in the atrial wall and in the

interventricular septum produce an array of small secreted peptides. These include

atriopeptin, atrial natriuretic polypeptide, cardiodilatin and cardionatrin which are

released into the surrounding capillaries. These hormones aid fluid maintenance and

electrolyte balance and decreased blood pressure.

Figure-13 The pathways of nerve impulse in the heart

The heart rate is controlled by the sinoatrial node, a pacemaker located at the junction

of the superior vena cava and the right atrium. These specialized nodal cardiac muscle

cells can spontaneously create an impulse that spreads over the atrial chamber wall by

internodal pathways to the atrioventricular node, located in the septal wall just above the

tricuspid valve. Modified cardiac muscle cells of the atrioventricular node transmits

signals to the myocardium of atria via the atrioventricular bundle bundle of His). Fibers

from the atrioventricular bundle pass down the interventricular septum to conduct the

impulse to the cardiac muscle through the modified cardiac muscle cells located in the

subendocardial connective tissue of right and left ventricle, known as Purkinje fibers.

Purkinje fibers also can be found in a few numbers in the limited area of right atrium and

in the interventricular septum


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EPICARDIUM

Figure-14 Epicardium

The epicardium , also known as visceral layer of the pericardium is composed of a

simpler squamous epithelium. The subepicardial layer of loose connective tissue contain

the coronary vessels, nerves and ganglia and an adipose tissue.

At the roots of the vessels entering and leaving the heart, the visceral pericardium

becomes continuous with the serous layer of the parietal pericardium. These two layers of

the pericardium enclose the pericardial cavity, a space containing a small amount of

serous fluid for lubricating the serous layer of the pericardium and the visceral

pericardium.


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Figure-15 The Pericardium

CARDIAC SKELETON

Cardiac skeleton is a structure that provide the structural framework for heart and

attachment sites for cardiac muscle and cardiac valve. The cardiac skeleton composed of

dense connective tissue includes three main components

1. septum membranaceum, that constituting the upper portion of the interventricular

septum, the atrioventricular foramina and atrial foramina.

2. trigonum fibrosum, that constituting some of cuspal area of the aortic valve

3. annuli fibrosi that formed around the base of the aorta, pulmonary artery, and

atrioventricular orifices.

The cardiac valve is a leaf like structure made by dense connective tissue that is

attached to the annuli fibrosi. There are 4 cardiac valve :


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Figure-16 The Heart Valves

1. Mitral or bicuspid valve consists of 2 leafs located between left atrium and left

ventricle

2. Tricuspid valve consists of 3 leafs located between right atrium and right

ventricle

3. The semilunar aortic valve consists of 3 leafs located between aorta and left

ventricle

4. The semilunar pulmonal valve consists of 3 leafs located between pulmonal and

right ventricle

The surface of cardiac valve is continuation of atrial and ventricle endocardium. The

edge of cardiac valve contains the corda tendinae, a fiber like structure composed by


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collagen fibers. The atrioventricular valve contains the small blood vessel, but the

semilunar valves are avascular.

Figure-17 The Section of Heart


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histologyofcardiovascular-2009

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