Mediastinum - Heart and Lungs

By Hermizan Halihanafiah

MediastinumThe central part of the thoracic cavity called mediastinum.It is between the lungs, extending from the sternum to

the vertebral column, and from neck to the diaphragm muscle.

Mediastinum contain all thoracic viscera except the lungs itself.

Among the structure in the mediastinum are the heart, esophagus, trachea, thymus and several large blood vessels.

Mediastinum can divide in 2 portion:an upper portion, above the

upper level of the pericardium, which is named the superior mediastinum with its superior limit at the superior thoracic opening and its inferior limit at the plane from the sternal angle to the intervertebral disc of T4-T5 (Plane of Ludwig);

Lower portion, below the upper level of the pericardium. This lower portion is again subdivided into three parts:that in front of the pericardium, the anterior

mediastinum that containing the pericardium and its contents, the

middle mediastinumand that behind the pericardium, the posterior

mediastinum

Lower Portion

It is surrounded by the chest wall anteriorly, the lungs laterally and the spine posteriorly. It is continuous with the loose connective tissue of the neck, and extends inferiorly onto the diaphragm.

Boundaries of the superior mediastinum (1)are: anterior - manubrium of the

sternum posterior - anterior surface of

bodies of vertebrae T1 through T4

superior - plane of the thoracic inlet

inferior - plane of the sternal angle

lateral - mediastinal pleura

Superior MediastinumThe superior

mediastinum is that portion of the which lies between the manubrium of sternum anteriorly, and the upper thoracic vertebrae posteriorly.

Superior MediastinumThis image shows the

structures of the superior mediastinum in tact.

Then we will start from the anterior boundary and work our way through the superior mediastinum from anterior to posterior.

With the thorax in tact, the first thing you see when you get ready to study the superior mediastinum is the manubrium of the sternum and the cartilage of the first rib.

These structures make up the anterior boundary.

The first plane is the glandular plane. The gland is what is left of the thymus.

It consists of two lobes and is mainly fat in the adult with small islets of active thymic cells scattered throughout.

The second plane is the venous plane and consists of the: left brachiocephalic vein right brachiocephalic

vein superior vena cava Intercostal veinarch of the azygos vein

The third plane is the arterial-nervous plane and consists of the:

aortic arch and its branches brachiocephalic artery left common carotid artery left subclavian artery

nerves include the: left and right vagus nerves left and right phrenic

nerves Arch Of Aorta

Phrenic Nerve

Vagus Nerve

Brachiocephalic Artery

Left Common Carotid Artery

LeftSubclavian

Artery

The fourth plane is the visceral plane and includes the: trachea esophagus left recurrent laryngeal

nerve (larynx nerve)

The fourth plane is the visceral plane and includes the: trachea esophagus left recurrent laryngeal

nerve

The fifth plane is the lymphatic plane and consists of the: thoracic duct

muscles origins of the

Sternohyoid and Sternothyroid

lower ends of the Longus coli

Anterior Mediastinum

The anterior mediastinum exists only on the left side where the left pleura diverges from the mid-sternal line.

It is narrow, above, but widens out a little below.

BoundariesIt is bounded:in front by the sternum laterally by the pleurae posteriorly by the pericardium anteriorly by the left Transversus thoracis and the

fifth, sixth, and seventh left costal cartilages

ContentsIt contains:a quantity of loose areolar tissuesome lymphatic vessels which ascend from the

convex surface of the liver two or three anterior mediastinal lymph glands the small mediastinal branches of the internal

thoracic artery

Middle MediastinumThe middle

mediastinum is the broadest part of the interpleural space. It is made up of the pericardial sac and its contents.

ContentsIt contains:the heart enclosed in the pericardium the ascending aorta the lower half of the superior vena cava with the azygos

vein opening into it the bifurcation of the trachea and the two bronchi the pulmonary artery dividing into its two branches the right and left pulmonary veins the phrenic nerves some bronchial lymphatic glands

Posterior MediastinumThe posterior

mediastinum is an irregular triangular space running parallel with the vertebral column.

BoundariesIt is bounded:anteriorally by the pericardium (in front of) inferiorally by the thoracic surface of the diaphragm

(below). superiorally by the transverse thoracic plane (above).

This plane is marked by an imaginary line travelling through the manubriosternal joint to the dividing line between the fourth and fifth thoracic vertebrae.

Boundariesposteriorally by the bodies of the vertebral column

from the lower border of the fourth to the twelfth thoracic vertebra (behind).

laterally: by the mediastinal pleura (on either side)

Contentsartery

thoracic part of the descending aorta veins

azygos vein the hemiazygos vein and the accessory hemiazygos vein

nerves vagus nerve splanchnic nerves (Sympathetic nerve)

esophagus thoracic ductsome lymph glands

After the heart has been removed, you will see the cut borders of the major vessels entering and leaving the heart. The oblique pericardial sinus is clearly seen within the four pulmonary veins and inferior vena cava at this point.

The arrow at the top represents the division between the superior mediastinum above and the inferior mediastinum below.

In Level 2, the pericardium has been removed and the esophagus can seen along with its plexus derived from the left and right vagus nerves as well as branches from the sympathetic chain.

As the esophagus passes through the diaphragm to enter the abdomen, the left vagus emerges from the plexus as the anterior vagal trunk and the right vagus becomes the posterior vagal trunk.

You can also see that the trachea splits into the right and left primary bronchi at the level of the junction between the superior and inferior mediastinum .

Once the esophagus has been studied, the next level to check out is the thoracic aorta.

The thoracic aorta starts at the T4-T5 junction and extends the full length of the posterior mediastinum passing through the aortic hiatus of the diaphragm into the abdomen.

The thoracic aorta gives rise to the posterior intercostal arteries

which pass posterior and lateral to join the posterior intercostal veins and intercostal nerves to form the neurovascular bundle

That travels along the inferior border of a rib or the upper aspect of an intercostal space.

It also gives rise to bronchial branches that enter the root of the lung to supply the bronchi and lung tissue.

Alongside and behind the thoracic duct, you will find the veins that drain the walls of the thorax, the azygos and hemiazygos veins.

Each of these veins begin in the abdomen as the ascending lumbar veins. The ascending lumbar veins drain parts of the posterior abdominal wall.

The next structures in the posterior mediastinum would be the splanchnic nerves, specifically the greater splanchnic nerves.

These nerves are derived from the sympathetic chains, thoracic ganglion T5 to T10.

There is also lesser splanchnic nerves that are derived from ganglion T10 and T11.

The most posterior item in the posterior mediastinum is the anterior longitudinal ligament which completely covers the anterior surfaces of the bodies of the vertebrae.

This extends from the sacral part of the vertebral column all the up to the skull.

Heart

Cone shaped12 cm long, 9 cm wide, 6 cm thickMass average 250 g in adult females, 300 g in adult

malesRest at diaphragm, near the midline of the thoracic

cavity.Lies in the middle mediastinum.2/3 of the mass of the heart lies to the left of the body

midline.

The pointed end of the heart is the apex.

Apex – directed anteriorly, inferiorly and to the left.

The broad portion of the heart opposite the apex is

the base.

Base – directed posteriorly, superiorly and to the

right.

Anterior surface (sternocostal surface) is deep to the

sternum and ribs.

The inferior surface is the part of the heart between

the apex and right border and rests mostly on the

diaphragm.

The right border faces the right lung and extends

from the inferior surface to the base.

Also note the three borders of the heart: right border (1) made up

of the right atrium inferior border (2) made

up of right atrium, right ventricle and left ventricle

left border (3) made up of the left ventricle

The left border, also called the pulmonary border, faces the left lung and extends from the base to the apex.

Note that the anterior surface shows parts of each of the four chambers of the heart: right atrium (RA) left atrium (LA) right ventricle (RV) left ventricle (LV)

Coronary SulcusWhen the vessels are removed from the heart, certain

sulci (grooves) can be seen and separated the various chambers of the heart.

From the anterior view of the heart, the anterior interventricular and coronary sulci can be seen (the darker brown areas).

The anterior interventricular sulcus separates the right and left ventricles.

The anterior part of the coronary sulcus separates the right atrium from the right ventricle.

Coronary Sulcus

From the posterior view of the heart, the posterior part of the coronary sulcus and the posterior interventricular sulcus can be seen.

From this view, the coronary sulcus can be seen to separate the left and right atria from the left and right ventricles.

The posterior interventricular sulcus separated the right ventricle from the left ventricle and if followed inferiorly, it can be seen to be almost continuous with

the anterior interventricular sulcus.

Coronary Sulcus

PericardiumMembrane that surround and protect the heart

Confine the heart into its position in the

mediastinum.

Allowing sufficient freedom and movement

vigorous and rapid contraction.

Consists 2 layers; superficial fibrous pericardium

and deeper serous pericardium.

Superficial Fibrous PericardiumSuperficial fibrous pericardium is a tough, inelastic,

dense irregular connective tissue.

Resembles bag that rest on and attaches to the

diaphragm.

Prevents overstretching, provide protection and

anchors the heart in the mediastinum.

Deeper Serous PericardiumThinner, more delicate membrane, forms a double

layer around the heart.Outer layer is a parietal layerInner layer is a visceral layer @ epicardiumBetween parietal and visceral layer – pericardial

cavityPericardial cavity contain pericardial fluidPericardial fluid – reduce friction between 2

membranes as the heart move.

Pericardium

Layers of the Heart WallEpicardium (external)

Myocardium (middle)

Endocardium (internal)

Epicardium@ visceral layer of the

serous pericardiumThin, transparentSmooth, slippery texture

to the outermost surface of the heart.

Myocardium Cardiac muscle tissueMakes up the bulk of

the heart.Responsible for its

pumping action.Involuntary

EndocardiumInnermostThin layerProvide smooth lining

for the chambers of the heart and covers the heart valves.

Chambers of the HeartRight atriumRight ventricleLeft atriumLeft ventricle

Right AtriumReceive blood from superior and inferior vena

kava, and coronary sinus.Anterior and posterior walls within the right

atrium is differ.Posterior walls is smooth, anterior wall is rough

due to the presence of muscular ridges called pectinate muscles.

Between the right and left atrium is a thin partition called interatrial septum.

Right AtriumA prominent feature of this septum is an oval

depression called the fossa ovalis.Blood passes from the right atrium to the right

ventricle through tricuspid valve.

Right VentricleForms most of the anterior surface of the heart.Inside – contains a series of ridges formed by raised of

cardiac muscles fibers called trabeculae carneae.The cusps of tricuspid valve are connected to

tendonlike cords, called chordae tendineae.Chordae tendineae connected to cone-shaped

trabeculae carneae called papillary muscles.

The right ventricle separate from left ventricle by a partition called interventricular septum.

Blood passes from right ventricle through the pulmonary valve into a large artery called pulmonary trunk

Pulmonary trunk will divide into left and right pulmonary arteries.

Left AtriumForms most of the base of the heartReceive blood from 4 pulmonary veins.Inside the left atrium; anterior and posterior wall

also is smooth.Blood passes from the left atrium to the left ventricle

through bicuspid (mitral) valve.

Left VentricleForms apex of the heartContain trabeculae carneae and has chordae

tendineae that anchor the cusps of the bicuspid valve to papillary muscles.

Blood passes from left atrium through aortic valve into the largest artery, arch of aorta.

Some blood in the aorta flows into the coronary arteries, which branch from the ascending aorta and carry blood to the heart wall.

Nerve SupplyThe strength and frequency of the

heart beat is controlled by the autonomic nervous system. Both parasympathetic and sympathetic parts of the autonomic nervous system are involved in the control of the heart.

The sympathetic fibers arise from segments T2-T4 of the spinal cord and are distributed through the middle cervical and cervico-thoracic (or stellate) ganglia and the first four ganglia of the thoracic sympathetic chain.

The sympathetic fibers pass into the cardiac plexus and from there to the SA node and the cardiac muscle.

The effect of the sympathetic nerves at the SA node is an increase in heart rate.

The effect on the muscle is an increase in rise of pressure within the ventricle, thus increasing stroke volume

The vagus provides the parasympathetic control to the heart.

The effect of the vagus at the SA node is the opposite of the sympathetic nerves, it decreases the heart rate.

It also decreases the excitability of the junctional tissue around the AV node and this results in slower transmission.

Strong vagal stimulation here may produce AV block

Conduction SystemThe heart also has an internal

nervous system made up of the SA (sinuatrial node) and the AV (atrioventricular) node.

The AV bundle (His) leaves the AV node near the lower part of the interatrial septum and splits over the upper part of the interventricular septum into a left bundle branch (LBB) and a right bundle branch (RBB).

Then impuls will send to the Purkinje Fibers – ventricle contraction

Systemic CirculationThe systemic circulation

includes the flow of oxygenated blood from the heart to the tissues in all parts of the body and the return of deoxygenated blood back to the heart.

The blood vessels, including the arteries, capillaries, and veins, are the main parts of systemic circulation.

Through systemic circulation, oxygen and nutrients are delivered to the body tissues via the arteries.

Blood is filtered during systemic circulation by the kidneys (most of the waste) and liver (sugars).

The systemic circulatory system is complex and its functions vary.

The systemic circulatory system is divided into subsystems for particular regions of the body.

Jugular Vein

Pulmonary ArterySuperior Vena Kava

Inferior Vena Kava

Hepatic vein

Hepatic Portal Vein

Renal Vein

Iliac Artery

Carotid Artery

Pulmonary Artery

Aorta

Mesentric Artery

Renal Artery

IliacVein

CORONARY CIRCULATION

Coronary CirculationNutrient could not diffuse quickly enough from

blood in the chambers of the heart to supply all

layers of cells that make up the heart wall.

For this reason, the myocardium has its own blood

vessels called coronary circulation.

Consists coronary arteries and coronary veins.

Coronary Arteries2 coronary arteries, the right and left coronary

arteries, branch from the ascending aorta and supply

oxygenated blood to myocardium.

The left coronary artery passes inferior and devide

into anterior inventricular branch (left anterior

decending artery) and circumflex branches.

Anterior interventricular branch supply oxygenated blood to the walls of ventricles.

The circumflex branch distributes oxygenated blood to the walls of the left ventricle and left atrium.

The right coronary artery gives off small atrial branches that supply the right atrium.

Then its continues inferiorly and divide into posterior interventricular branch and marginal branch.

Posterior interventricular branch supplies the walls of 2 ventricles with oxygenated blood.

The right marginal branch carries oxygenated blood to the myocardium of the right ventricle.

Figure 19.11b

Coronary VeinsAfter blood passes through coronary arteries, it

flows into capillaries, where it delivers oxygen and nutrient and collect CO2 and waste product into veins.

The deoxygenated blood then drains into a large vascular veins called coronary sinus, located at the posterior surface of the heart.

Coronary will empties into right atrium.The main tributaries carrying blood into the coronary

sinus are:Great cardiac vein – drains the anterior aspect of the

heart.Middle cardiac vein – drain the posterior aspect of the

heart.

Figure 19.11b

LungsPaired cone shaped organ in the thoracic cavity

Separated each other by the heart and other structures in the mediastinum.

2 layers of serous membrane, called the pleural membrane enclose and protect the lungs.

The superficial layer lines the wall of the thoracic cavity called the parietal pleura.

The deep layers cover the lungs themselves call visceral pleura.

Figure 10.16 The relationship of the pleura to the lungs.

Copyright © Elsevier Ltd 2005. All rights reserved.

Between the visceral and prietal pleurae is a small space called pleural cavity.

Pleural cavity contains small amount of lubricating fluid called pleural fluid.

Pleural fluid reduces friction between 2 membranes, allowing them to slide easily over one another during breathing.

pleural fluid also causes the 2 membranes to adhere to one another. (surface tension)

The lungs extend from the diaphragm to just slightly superior to the clavicles and lie against the ribs anteriorly and posteriorly.

The broad inferior portion of the lung, the base, is concave and fits over the convex area of the diaphragm.

The narrow superior portion of the lung is the apex.

The surface of the lung lying against the ribs, the costal surface, matches the rounded curvature of the ribs.

The mediastinal (medial) surface of each lung contain the region, the hilus, through which bronchi, pulmonary blood vessel, lymphatic vessels,

These structure are held together by the pleura and connective tissue and constitute the roots of the lung.

Medially, the left lung also contains a concavity, the cardiac notch, in which the heart lies.

Apex of the lungs lies superiorly to the medial third of the clavicles

Anterior, lateral, and posterior surface of the lungs lie against the ribs.

Base of the lung extends from the 6th costal cartilage anteriorly to the spinous process of the T10 posteriorly.

The pleura extend about 5cm below the base from the 6th costal cartilage anteriorly to the 12th rib posteriorly.

Lobe and FissureThe left lung has 2 lobes (superior, inferior) and the

right lung has 3 lobes (superior, inferior, middle). The bulk of the lung surface is against the ribs and is

called the costal surface. Other surfaces include the diaphragmatic and

mediastinal. Each lung also has 3 borders: anterior, posterior and

inferior.In both lungs, the superior and inferior lobes are

separated by the oblique fissure.In the right lung, the superior lobe is further divided

into the superior and middle lobes, which are separated by the horizontal fissure.

Oblique Fissure

Horizontal Fissure

Oblique Fissure

RIGHT LUNG LEFT LUNG

The anterior border of the left lung is pushed out by the heart and this notch is called the cardiac notch. If you follow this notch inferiorly, you will find a small lingular lobe

Root of the right lung bronchi lie posterior pulmonary arteries are

superior pulmonary veins are

inferior and anterior

Root of the left lung bronchus lies posterior pulmonary artery is

superior pulmonary vein is

inferior and anterior

On the mediastinal surface of the right lung, you will find these structures azygos vein and its arch

(over the root of the lung) phrenic nerve anterior to the

root of the lung vagus nerve posterior to the

root of the lung esophagus

On the mediastinal surface of the left lung, you will find these structures:descending aorta arch of the aorta over the

root of the lung right common carotid artery right subclavian artery phrenic nerve anterior to

the root of the lung vagus nerve posterior to the

root of the lung

Blood Supply to Lungs2 sets of artery

Pulmonary arteriesBronchial arteries

Pulmonary ArteriesDeoxygenated blood passes through the pulmonary

trunksDivide into left and right pulmonary arteriesEnter left and right lungsReturn oxygenated blood to the heart (left atrium)

through 4 pulmonary veins.

Bronchial arteryBranch from the aortaDeliver oxygenated blood to the lungs tissuesThis blood perfuse the walls of bronchi and bronchioles.Deoxygenated blood return to the heart through

pulmonary arterySome blood, however drains into bronchial veins,

branches of the azygos system returns to the heart via superior vena kava.