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THORACIC WALL, MEDIASTINUM
&
HEART & PERICARDIUM
27.September.2011 Tuesday
THORACIC WALL
1. Thorax
The thorax is the part of the body between the neck and abdomen.
Posterior surface is formed by the 12 thoracic vertebræ and the posterior parts of the ribs.
Anterior surface is formed by the sternum and costal cartilages.
Lateral surfaces are formed by the ribs, separated from each other by the intercostal spaces, eleven in
number, which are occupied by the intercostal muscles and membranes.
The floor of the thoracic cavity is deeply invaginated inferiorly (i.e., is pushed upward) by viscera of the
abdominal cavity.
Regions
• Thoracic wall
• Thoracic cavity
The thorax includes the primary organs of the respiratory and cardiovascular systems. The majority of
the thoracic cavity is occupied by the lungs, which provide for the exchange of oxygen and carbon dioxide
between the air and blood. Most of the remainder of the thoracic cavity is occupied by the heart and
structures involved in conducting the air and blood to and from the lungs. Additionally, nutrients (food)
traverse the thoracic cavity via the esophagus, passing from the site of entry in the head to the site of
digestion and absorption in the abdomen.
2. Thoracic Wall
The true thoracic wall includes the thoracic cage and the muscles that extend between the ribs as
well as the skin, subcutaneous tissue, muscles, and fascia covering its anterolateral aspect. The same
structures covering its posterior aspect are considered to belong to the back. The mammary glands of the
breasts lie within the subcutaneous tissue of the thoracic wall.
The domed shape of the thoracic cage provides its components enabling to:
 Protect vital thoracic and abdominal organs (most air or fluid filled) from external forces.
 Resist the negative (sub-atmospheric) internal pressures generated by the elastic recoil of the lungs
and inspiratory movements.
 Provide attachment for and support the weight of the upper limbs.
 Provide the anchoring attachment (origin) of many of the muscles that move and maintain the
position of the upper limbs relative to the trunk, as well as provide the attachments for muscles of the
abdomen, neck, back, and respiration.
The thorax is one of the most dynamic regions of the body. With each breath, the muscles of the thoracic
wall—working in concert with the diaphragm and muscles of the abdominal wall—vary the volume of the
thoracic cavity, first by expanding the capacity of the cavity, thereby causing the lungs to expand and draw
air in and then, due to lung elasticity and muscle relaxation, decreasing the volume of the cavity and causing
them to expel air.
3. Skeleton of Thoracic Wall
The thoracic skeleton forms the osteocartilaginous thoracic cage, which protects the thoracic viscera
and some abdominal organs. The thoracic skeleton includes 12 pairs of ribs and associated costal cartilages,
12 thoracic vertebrae and the intervertebral (IV) discs interposed between them, and the sternum. The ribs
and costal cartilages form the largest part of the thoracic cage; both are identified numerically, from the most
superior (1st rib or costal cartilage) to the most inferior (12th).
3.1.Thoracic Vertebrae
Characteristic features of thoracic vertebrae include:
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 Most thoracic vertebrae are typical in that they have bodies, vertebral arches, and seven processes for
muscular and articular connections
 Bilateral costal facets (demifacets) on the vertebral bodies, usually occurring in inferior and superior
pairs, for articulation with the heads of ribs. Atypical thoracic vertebrae are 1, 10 (sometimes), 11 and 12
have single facets.
 Costal facets on the transverse processes
 Spinous processes.
Typically, two demifacets paired and the posterolateral margin of the IV disc between them form a single
socket to receive the head of the rib of the same identifying number as the inferior vertebra (e.g., head of rib
6 with the superior costal facet of vertebra T6).
3.2. Ribs, Costal Cartilages, and Intercostal Spaces
Ribs (L. costae) are curved, flat bones that form most of the thoracic cage. There are three types of ribs that
can be classified as typical or atypical:
 True (vertebrocostal) ribs (1st-7th ribs): They attach directly to the sternum through their own costal
cartilages.
 False (vertebrochondral) ribs (8th, 9th, and usually 10th ribs): Their cartilages are connected to the
cartilage of the rib above them; thus their connection with the sternum is indirect.
 Floating (vertebral, free) ribs (11th, 12th, and sometimes 10th ribs): The rudimentary cartilages of
these ribs do not connect even indirectly with the sternum; instead they end in the posterior abdominal
musculature.
Typical ribs (3rd-9th) have the following components:
 Head: wedge-shaped and has two facets, separated by the crest of the head; one facet for articulation
with the numerically corresponding vertebra and one facet for the vertebra superior to it.
 Neck: connects the head of the rib with the body at the level of the tubercle.
 Tubercle: located at the junction of the neck and body; articulates with the corresponding transverse
process of the vertebra, and a rough nonarticular part provides attachment for the costotransverse ligament.
 Body (shaft): thin, flat, and curved, most markedly at the costal angle where the rib turns anterolaterally.
The angle also demarcates the lateral limit of attachment of the deep back muscles to the ribs. The concave
internal surface of the body has a costal groove paralleling the inferior border of the rib, which provides
some protection for the intercostal nerve and vessels.
Atypical ribs 1st, 2nd, and 10th-12th ribs are dissimilar.
Costal cartilages prolong the ribs anteriorly and contribute to the elasticity of the thoracic wall, providing a
flexible attachment for their anterior ends.
Intercostal spaces separate the ribs and their costal cartilages from one another. The spaces are named
according to the rib forming the superior border of the space—for example, the 4th intercostal space lies
between ribs 4 and 5. There are 11 intercostal spaces and 11 intercostal nerves. Intercostal spaces are
occupied by intercostal muscles and membranes, and two sets (main and collateral) of intercostal blood
vessels and nerves, identified by the same number assigned to the space.
Sternum (Breastbone, Tr. iman tahtası)
The sternum (G. sternon, chest) is the long, flat bone that forms the middle of the anterior part of the
thoracic cage. It directly overlies and affords protection for mediastinal viscera in general and much of the
heart in particular. The sternum is commonly known as the breastbone and is divided into three areas, the
upper manubrium, the body, and the xiphoid process. The manubrium and body of the sternum lie in slightly
different planes superior and inferior to their junction, the manubriosternal joint; hence, their junction forms
a projecting sternal angle (of Louis).
4. Thoracic Apertures
While the thoracic cage provides a complete wall peripherally, it is open superiorly and inferiorly.
The much smaller superior opening is a passageway that allows communication with the neck and upper
limbs. The larger inferior opening provides the ring-like origin of the diaphragm, which completely occludes
the opening.
Structures that pass between the thoracic cavity and the neck through the superior thoracic aperture:
Trachea
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Esophagus
Nerves, and vessels that supply and drain the head, neck, and upper limbs
Joints of Thoracic Wall
Although the joints between the bones of the thorax has limited movement ability, the whole outcome of
these movements permit expansion of the cavity during inspiration. During inspiration, the thoracic cavity
can expand in antero-posterior, vertical and transverse dimensions.
1. Costa transverse joints
2. Sterno costal joint
3. Costachondralis joint
4. Intercondral Joints
5. Sternal Joints
Muscles of Thoracic Wall
Some muscles attached to and/or covering the thoracic cage are primarily involved in serving other
regions. Several (axioappendicular) muscles extend from the thoracic cage (axial skeleton) to bones of the
upper limb (appendicular skeleton). Muscles, such as sternocleidomasteoid muscle, abdominal muscles,
pectoral muscles, function as accesory muscles of respiraton and work in forced respiration; when the person
needs to breathe in and out more than usual; 100 meter sprinters, patients with respiratory problems.
Muscles of the thoracic wall
– Serratus posterior muscles
– Levator costarum muscles
– Intercostal muscles(External, internal and innermost)
– Subcostal muscle
– Transverse thoracic muscle
These muscles either elevate or depress the ribs helping to increse the volume of the thoracic cavity.
The diaphragm is a shared wall (actually floor/ceiling) separating the thorax and abdomen.
Although it has functions related to both compartments of the trunk, its most important (vital) function is
serving as the primary muscle of inspiration.
6. Vasculature of Thoracic Wall
In general, the pattern of vascular distribution in the thoracic wall reflects the structure of the thoracic
cage—that is, it runs in the intercostal spaces, parallel to the ribs.
7.1. Arteries of Thoracic Wall
The arterial supply to the thoracic wall derives from the branches of the:
 Thoracic aorta
 Subclavian artery
 Axillary artery
The intercostal arteries course through the thoracic wall between the ribs.
4.2. Veins of Thoracic Wall
The intercostal veins accompany the intercostal arteries and nerves and lie most superior in the costal
grooves. There are 11 posterior intercostal veins and one subcostal vein on each side. The posterior
intercostal veins anastomose with the anterior intercostal veins (tributaries of internal thoracic veins).
Most posterior intercostal veins (4-11) end in the azygos/hemiazygos venous system, which conveys venous
blood to the superior vena cava (SVC).
5. Nerves of Thoracic Wall
The 12 pairs of thoracic spinal nerves supply the thoracic wall. As soon as they leave the IV foramina
in which they are formed, the mixed thoracic spinal nerves divide into anterior and posterior (primary) rami
or branches. The anterior rami of nerves T1-T11 form the intercostal nerves that run along the extent of the
intercostal spaces.
The intercostal nerves pass to and then continue to course in or just inferior to the costal grooves,
running inferior to the intercostal arteries (which, in turn, run inferior to the intercostal veins). The
neurovascular bundles (and especially the vessels) are thus sheltered by the inferior margins of the overlying
rib.
6.1. Dermatomes
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Through its posterior ramus and the lateral and anterior cutaneous branches of its anterior ramus,
most thoracic spinal nerves (T2-T12) supply a strip-like dermatome of the trunk extending from the
posterior median line to the anterior median line. The skin area supplied by a segment of the spinal cord.
6.2. Atypical Intercostal nerves
1st intercostal nerve
2nd intercostal nerve
7th-11th intercostal nerve
12th intercostal nerve
7. Breasts
The breasts are the most prominent superficial structures in the anterior thoracic wall, especially in
women. The breasts (L. mammae) consist of glandular and supporting fibrous tissue embedded within a fatty
matrix, together with blood vessels, lymphatics, and nerves. Both men and women have breasts; normally
they are well developed only in women. The mammary glands are in the subcutaneous tissue overlying the
pectoralis major and minor muscles. At the greatest prominence of the breast is the nipple, surrounded by a
circular pigmented area of skin, the areola (L. small area).
The mammary glands within the breasts are accessory to reproduction in women. They are rudimentary and
functionless in men, consisting of only a few small ducts or epithelial cords. Usually, the fat present in the
male breast is not different from that of subcutaneous tissue elsewhere, and the glandular system does not
normally develop.
7.1. Female Breasts
The amount of fat surrounding the glandular tissue determines the size of non-lactating breasts. The
roughly circular body of the female breast rests on a bed that extends transversely from the lateral border of
the sternum.
The arterial supply of the breast:
1. Medial mammary branches
2. Lateral mammary branches, lateral thoracic and thoracoacromial arteries
3. Posterior intercostal arteries 2nd-4th
The venous drainage of the breast is mainly to the axillary vein, but there is some drainage to the internal
thoracic vein.
The lymphatic drainage of the breast is important because of its role in the metastasis of cancer cells.
Most lymph, especially from the lateral breast quadrants, drains to the axillary lymph nodes. Most of the
remaining lymph, particularly from the medial breast quadrants, drains to the parasternal lymph nodes or to
the opposite breast, whereas lymph from the inferior quadrants may pass deeply to abdominal lymph nodes.
The nerves of the breast derive from anterior and lateral cutaneous branches of the 4th-6th intercostal nerves.
MEDIASTINUM
(Interpleaural space)
The thoracic cavity is divided into three major spaces: the central compartment or mediastinum that
houses the thoracic viscera except for the lungs and, on each side, the right and left pulmonary cavities
housing the lungs.
The mediastinum (Mod. L. middle septum, L, mediastinus, midway), occupied by the mass of tissue
between the two pulmonary cavities, is the central compartment of the thoracic cavity. It is covered on
each side by mediastinal pleura and contains all the thoracic viscera and structures except the lungs.
Mediastinum extends from superior thoracic aperture superiorly to the diaphragm inferiorly and from
sternum and costal cartilages anteriorly to to the bodies of the thoracic vertebrae posteriorly.
The looseness of the connective tissue and the elasticity of the lungs and parietal pleura on each side
of the mediastinum enable it to accommodate movement as well as volume and pressure changes in the
thoracic cavity, for example, those resulting from movements of the diaphragm, thoracic wall, and
tracheobronchial tree during respiration, contraction (beating) of the heart and pulsations of the great
arteries, and passage of ingested substances through the esophagus.
The mediastinum is divided into superior and inferior parts for purposes of description.
• Superior mediastinum
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– Superior to sternal angle
Inferior mediastinum: Inferior to sternal angle
• Anterior mediastinum
– Between the anterior surface of pericardium and posterior surface of the sternum
• Middle mediastinum
– Pericardium, heart and beginings of the great vessels emerging from the heart lie here
• Posterior mediastinum
– Lies posterior to the pericardium and diaphragm
Some structures, such as the esophagus, pass vertically through the mediastinum and therefore lie in more
than one mediastinal compartment.
Contents of the superior mediastinum
1) Thymus
2) Great vessels related to the heart with the veins
3) Inferior continuation of the cervical viscera (trachea anteriorly and esophagus posteriorly) and related
nerves (left recurrent laryngeal nerve)
4) Thoracic duct and lymphatic trunks
5) Prevertebral muscles
Anterior mediastinum
It lies between the sternum anteriorly and the pericardium posteriorly. Superiorly it continues with the
superior mediastinum starting at the level of sternal angle.
Contents of the anterior mediastinum
Remnants of thymus
Branches of the internal thoracic artery
Posterior Mediastinum
The posterior mediastinum (the posterior part of the inferior mediastinum) is located inferior to the sternal
angle, posterior to the pericardium and diaphragm, and between the parietal pleura of the two lungs.
Contents of the posterior mediastinum
• Thoracic aorta
• Thoracic duct
• Posterior mediastinal lymph nodes
• Azygos and hemiazygos veins
• Esophagus
• Esophageal nerve plexus
• Thoracic sympathetic trunks
• Thoracic splanchnic nerves
HEART & PERICARDIUM
.
HEART
The heart, slightly larger than a clenched fist, is a double, self-adjusting suction and pressure pump,
the parts of which work in unison to propel blood to all parts of the body.
The right side of the heart (right heart) receives poorly oxygenated (venous) blood from the body through the
superior vena cava (SVC) and inferior vena cava (IVC) and pumps it through the pulmonary trunk and
arteries to the lungs for oxygenation. The left side of the heart (left heart) receives well-oxygenated (arterial)
blood from the lungs through the pulmonary veins and pumps it into the aorta for distribution to the body.
The heart has four chambers: right and left atria and right and left ventricles. The atria are receiving
chambers that pump blood into the ventricles (the discharging chambers). The synchronous pumping actions
of the heart's two atrioventricular (AV) pumps (right and left chambers) constitute the cardiac cycle. The
cycle begins with a period of ventricular elongation and filling (diastole) and ends with a period of
ventricular shortening and emptying (systole).
The wall of each heart chamber consists of three layers, from superficial to deep:
 Endocardium, a thin internal layer
 Myocardium, a thick, helical middle layer composed of cardiac muscle.
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
Epicardium, a thin external layer
Externally, the atria are demarcated from the ventricles by the coronary sulcus (atrioventricular
groove), and the right and left ventricles are demarcated from each other by anterior and posterior
interventricular (IV) sulci (grooves). The heart appears trapezoidal from an anterior or posterior view, but in
three dimensions it is shaped like a tipped-over pyramid with its apex (directed anteriorly and to the left), a
base (opposite the apex, facing mostly posteriorly), and four sides.
The four surfaces of the heart are the:
 Anterior (sternocostal) surface
 Diaphragmatic (inferior) surface
 Right pulmonary surface
 Left pulmonary surface
Right atrium
The right atrium forms the right border of the heart and receives venous blood from the SVC, IVC,
and coronary sinus. The ear-like right auricle is a conical muscular pouch that projects from this chamber
like an add-on room, increasing the capacity of the atrium as it overlaps the ascending aorta.
The interior of the right atrium has a smooth, thin-walled, posterior part (the sinus venarum) on which the
venae cavae (SVC and IVC) and coronary sinus open, bringing poorly oxygenated blood into the heart.
The interatrial septum separating the atria has an oval, thumbprint-size depression, the oval fossa (L. fossa
ovalis), which is a remnant of the oval foramen (L. foramen ovale) and its valve in the fetus.
Right ventricle
The right ventricle forms the largest part of the anterior surface of the heart, a small part of the
diaphragmatic surface, and almost the entire inferior border of the heart. The right ventricle receives blood
from the right atrium through the right AV (tricuspid) orifice. Tendinous cords (L. chordae tendineae)
attach to the free edges and ventricular surfaces of cusps, much like the cords attaching to a parachute. The
tendinous cords arise from the apices of papillary muscles, which are conical muscular projections with
bases attached to the ventricular wall. Regurgitation of blood (backward flow of blood) from the right
ventricle back into the right atrium is blocked during ventricular systole by the valve cusps. The
interventricular septum (IVS), is obliquely placed partition between the right and left ventricles.
Left Atrium
The left atrium forms most of the base of the heart. The valveless pairs of right and left pulmonary
veins enter the atrium. The tubular, muscular left auricle, its wall trabeculated with pectinate muscles, forms
the superior part of the left border of the heart. A semilunar depression in the interatrial septum indicates the
floor of the oval fossa; the surrounding ridge is the valve of the oval fossa (L. valvulae foramen ovale).
The interior of the left atrium has:
 Pectinate muscles
 Four pulmonary veins (two superior and two inferior)
 An interatrial septum
 A left AV orifice through which the left atrium discharges the oxygenated blood it receives from the
pulmonary veins into the left ventricle.
Left Ventricle
The left ventricle forms the apex of the heart, nearly all its left (pulmonary) surface and border, and most of
the diaphragmatic surface. Because arterial pressure is much higher in the systemic than in the pulmonary
circulation, the left ventricle performs more work than the right ventricle.
The interior of the left ventricle has:
 A smooth-walled, non-muscular, superoanterior outflow part, the aortic vestibule, leading to the
aortic orifice and aortic valve.
 A double-leaflet mitral valve that guards the left AV orifice.
The mitral valve has two cusps. The semilunar aortic valve, between the left ventricle and the ascending
aorta, is obliquely placed.
Vasculature of the Heart
The blood vessels of the heart comprise the coronary arteries and cardiac veins, which carry blood to
and from most of the myocardium.
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Arterial Supply of the Heart
The coronary arteries, the first branches of the aorta, supply the myocardium and epicardium. The
right and left coronary arteries arise from the corresponding aortic sinuses. Anastomoses between the
branches of the coronary arteries exist, which enables the development of the collateral circulation.
The coronary arteries supply both the atria and the ventricles.
The right coronary artery (RCA) arises from the right aortic sinus of the ascending aorta and runs
in the coronary sulcus. The left coronary artery (LCA) arises from the left aortic sinus of the ascending
aorta, and runs in the coronary sulcus.
Venous Drainage of the Heart
The heart is drained mainly by veins that empty into the coronary sinus and partly by small veins that
empty into the right atrium.
Lymphatic Drainage of the Heart
A single lymphatic vessel, formed by the union of various lymphatic vessels from the heart ends in the
inferior tracheobronchial lymph nodes, usually on the right side.
STIMULATING, CONDUCTING, AND REGULATING SYSTEMS OF HEART
Stimulating and Conducting System of the Heart
The conducting system consists of nodal tissue that initiates the heartbeat and coordinates
contractions of the four heart chambers, and highly specialized conducting fibers for conducting them
rapidly to the different areas of the heart. The impulses are then propagated by the cardiac striated muscle
cells so that the chamber walls contract simultaneously.
Impulse generation and conduction can be summarized as follows:
 The SA node (pacemaker of the heart; in the right atrium) initiates an impulse that is rapidly
conducted to cardiac muscle fibers in the atria, causing them to contract.
 The impulse spreads by myogenic conduction, which rapidly transmits the impulse from the SA node
to the AV node (in the right atrium).
 The signal is distributed from the AV node through the AV bundle and its branches (the right and left
bundles), which pass on each side of the IVS to supply subendocardial branches to the papillary
muscles and the walls of the ventricles.
Innervation of the Heart
Innervation of the heart is through the autonomic nerves (both sympathetic and parasympathetics)
from the cardiac plexus.
Septal Defects
Atrial Septal Defects (ASD): A congenital anomaly of the interatrial septum, usually incomplete
closure of the oval foramen, is an atrial septal defect (ASD).
Ventricular Septal Defects (VSD): The membranous part of the IVS is the common site of
ventricular septal defects (VSDs). VSDs rank first on all lists of cardiac defects. A VSD causes a left to
right shunt of blood through the defect.
Valvular Heart Disease
Disorders involving the valves of the heart disturb the pumping efficiency of the heart. Valvular heart
disease produces either stenosis (narrowing) or insufficiency. Stenosis is the failure of a valve to open fully,
slowing blood flow from a chamber. Insufficiency or regurgitation, on the other hand, is failure of the valve
to close completely, usually owing to nodule formation on (or scarring and contraction of) the cusps so that
the edges do not meet or align. This allows a variable amount of blood (depending on the severity) to flow
back into the chamber it was just ejected from. Both stenosis and insufficiency result in an increased
workload for the heart. Because valvular diseases are mechanical problems, damaged or defective cardiac
valves can be replaced surgically in a procedure called valvuloplasty.
Coronary Artery Disease or Coronary Heart Disease: Coronary artery disease (CAD) is one of the
leading causes of death. It has many causes, all of which result in a reduced blood supply to the vital
myocardial tissue.
Myocardial Infarction: With sudden occlusion of a major artery by an embolus (G. embolos, plug), the
region of myocardium supplied by the occluded vessel becomes infarcted (rendered virtually bloodless) and
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undergoes necrosis (pathological tissue death). The most common cause of ischemic heart disease is
coronary artery insufficiency resulting from atherosclerosis.
Angina Pectoris: Pain that originates in the heart is called angina or angina pectoris (L. angina, strangling
pain + L. pectoris, of the chest). Individuals with angina commonly describe the transient (15 sec to 15 min)
but moderately severe constricting pain as tightness in the thorax, deep to the sternum. The pain is the result
of ischemia of the myocardium that falls short of inducing the cellular necrosis that defines infarction.
PERICARDIUM
The pericardium is a fibroserous membrane that covers the heart and the beginning of its great
vessels. The pericardium is a closed sac composed of two layers.
The pericardium is a closed sac composed of two layers:
1) Fibrous pericardium (external)
continuous with the central tendon of the diaphragm
2) Serous pericardium (internal)
Parietal layer
Visceral layer (epicardium)
Visceral and parietal layers are continuous with each other where the great vessels enter and leave
the heart. Inner surface is lined by the parietal layer of the serous pericardium and these layers are strictly
attached to each other. The fibrous pericardium protects the heart against sudden overfilling because it is so
unyielding and closely related to the great vessels that pierce it superiorly.
The pericardial cavity is the potential space between opposing layers of the parietal and visceral
layers of serous pericardium. It normally contains a thin film of fluid that enables the heart to move and beat
in a frictionless environment. There are two potential spaces, i.e. sinuses in pericardium; transverse
pericardial sinus and oblique pericardial sinus. The arterial supply of the pericardium is mainly from a
slender branch of the internal thoracic artery. The venous drainage of the pericardium is from the
pericardiacophrenic veins. The nerve supply of the pericardium is from the phrenic nerves).
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