THORAX LECTURE

THORAX
:
THORACIC WALL
- Main function: house and protect vital heart and lungs
- Mobile to accommodate volume changes during respiration
- Thoracic wall: vertebrae, ribs, sternum, and muscles
- Superficial  Deep: Skin  superficial fascia  deep fascia  muscles

Vertebra: (Fig 1.1)
- Body, pedicle, lamina, transverse process, articular process, spinous process
- Vertebral foramens – collectively called vertebral canal, houses spinal cord

Ribs: (Fig 1.2)
- Head, neck, tubercle, body, angle, costal groove
- 12 ribs, 7 true, 8-10 false, and 11-12 floating
- 1st rib: highest, shortest, broadest, and most curved

Vertebral Column (Fig 1.3)
- intervertebral disc (joint of symphysis variety???), intervertebral foramen (spinal nerve/blood vessels run here)
- Rib articulates just superior to corresponding vertebrae (e.g Rib 5 is located b/w T4 and T5)

Sternum and Other Landmarks (Fig. 1.4)
- Sternum: manubrium, (sternal angle)- 2nd rib), body, and xiphoid process
- Costal cartilage (hyaline): connects directly to ribs 1-7, others connect to one above
- Jugular (suprasternal) notch, sternal angle, clavicle, sternoclavicular joint, acromion, coracoid process

Skin = protective organ
- Two layers: external Epidermis and Dermis
- Dermis (corium) = contains hair follicles, sebaceous glands, sweat glands, small blood vessels, terminal branches of cutaneous nerves
- deep to the skin, Subcutaneous tissue (superficial fascia) contains fat, blood vessels, superficial blood vessels
- deep to the Subcutaneous tissue, deep fascia envelopes the muscles
- Retinacula cutis – passes from skin through fat of superficial and deep fascia; attaches skin to deeper parts of the body, BUT allows considerable mobility

Breasts (Fig 1.7)
- Mammary Glands, modified sweat glands that by definition lie in superficial fascia, anterior to deep fascia of the pectoralis muscle
- Retromammary space b/w mammary gland and deep fascia, allows breast to move freely, site of breast implants & cancer, ie not attached to deep fascia of pectoralis
- Mammary gland is attached to overlying skin via fibrous bands, suspensory ligaments (Cooper’s ligaments) that pass from deep fascia to deep layer of skin
- Q: Why are breast round?
- A: Fat lies in compartments bounded by these areolar septa (b/w suspensory ligaments)
- Nipple (mammary papilla) found at ICS 4, rises from center of pigmented areola, which is rough due to small subcutaneous glands that produce lubrication for the nipple
- Lactiferous ducts (approx. 15-20 per mammary gland) drain corresponding glandular lobules and then converge and open to the nipple


Muscles, Nerves, and Vessels
- Platysma muscle is wide, thin, striated sheet that belongs to the facial expression muscle group; inferior portion lies over the clavicle

Cutaneous branches of spinal nerves (Fig 1.
- anterior branches emerge from intercostals spaces just lateral to sternal margin
- lateral cutaneous branches are larger & course in the superficial fascia
- lateral cutaneous T2 branch = intercostobrachial nerve, supplies skin and subcutaneous tissue on the back and medial side of the arm
- Serratus Anterior located laterally/posteriorly, run approx. parallel to ribs, the lateral cutaneous branch crosses through it (Fig 1.9)

Pectoralis Major fan-shaped muscle, sternocostal head originiating from sternum and ribs and the clavicular head originating from medial half of clavicle; two heads meet at the sternoclavicular joint
- pectoralis major tendon inserted in humerus, function adduction of humerus
- lateral pectoral nerve arises from the lateral cord of brachial plexus and then enters the deep surface of the pectoral major muscle
- medial pectoral nerve arises from the medial cord and supplies the pectoralis minor and part of the major (pierces minor before entering the major sternal head)
- Deltopectoral triangle is superior to clavicular head(of pectoralis major), and b/w it and the adjacent deltoid muscle, also contains the cephalic vein
- Thoracoacromial artery along with lateral pectoral nerve, enters the deep surface of clavicular head (of pectoralis major muscle)

Clavipectoral Fascia, Pectoralis Minor, and Subclavius
- Clavipectoral fascia contains vessels and nerves entering the deep surface of the pectoralis major and envelops the pectoralis minor and subclavius (slender muscle inferior to clavicle)
- Pectoralis Minor attaches to costal cartilages of ribs 2 through 5, distally it is inserted into the coracoid process of the scapula, important site for surgeons
- Cephalic vein (crosses the minor tendon and joins the axillary vein) and the Thoracoacromial artery (branch of the axillary artery) are major blood vessels that pierce through clavipectoral fascia
- Lateral thoracic artery is located lateral to the pectoralis minor (Fig 1.10)

Intercostal Spaces and Intercostal Muscles
- three muscle layers (superficial  deep): external, internal, innermost intercostals
- muscles are supplied by the corresponding intercostal nerve and intercostals vessels (VAN) that are located b/w the internal and innermost layers (Fig 1.11)
- these muscles are inspiratory; they elevate the ribs and keep the rib spaces rigid
- Internal thoracic vessels run vertically across the intercostal spaces, lateral to sternum; these vessels communicate with intercostal vessels (VAN)
- Internal thoracic (internal mammary) arteries are branches of the corresponding subclavician arteries (Fig 1.12, 1.13)

Anterior Thoracic Wall
- Internal thoracic vessels (right and left) are firmly attached to the anterior thoracic wall by several muscle slips of the transverses thoracis and by segmental arterial branches and venous tributaries
- Sternocostal joint – fine ligaments, joint capsule, and synovial cavity; slight gliding movements occur here during respiration
- Perichondrium surrounds costal cartilage

PLEURAL CAVITIES
- two openings/apertures: Superior and Inferior Throacic Apertures
- Superior Thoracic Aperture, thoracic inlet, is relatively small and is surrounded by the manubrium, paired first ribs, and first thoracic vertebrae; trachea, esophagus, vagus, major vessels pass b/w thorax and neck, while major blood vessels pass from thorax to upper limbs
-Inferior Thoracic Aperture, thoracic outlet, musculotendinous thoracic diaphragm separates the thoracic cavity from the abdominal cavity; aorta, IVC, esophagus pass b/w thorax and abdomen through special openings in the diaphragm
- Space within thorax contains two pleural cavities, right and left one, and a mediastinum (b/w pleural cavities) houses heart, aorta, trachea, and esophagus
- Lung is covered with smooth glistening membrane, pulmonary or visceral pleura
- Lung is attached to medistinum via isthmus (hilius???) through which airways and blood vessels enter or leave the organ; this region = root of the lung
- Visceral and parietal pleura are continuous at the root of the lung
-Parietal pleura: costal, mediastinal, diaphragmatic, and cupula (cervical)
- lines along which costal becomes diaphragmatic and mediastinal = pleura reflections
- Pleural recesses are sites of pleural reflections, lung rarely fills these spaces
- Costomedistinal recess – part of LEFT cavity, defined as parietal pleural reflection from the anterior portion of the thoracic wall to the medistinum
-Costodiaphragmatic recess – both cavities, located at most inferior limits of the parietal pleura (Fig 1.16)
- Endothoracic fascia – connective tissue plane that separates rib cage from the parietal pleura (of lung); provides cleavage plane for surgical separation of the pleura from the thoracic wall

LUNGS
- interlobar fissures divide lungs into lobes
- oblique fissures (both) are long and deep, divide lungs into superior and inferior
- horizontal fissure of right lung (divides superior/upper from middle)
- Right Lung: 3 lobes (upper/superior, middle, lower/inferior), shorter, more voluminous
- Left Lung: 2 lobes (superior and inferior)
- Pericardial sac contains the heart
- Root of lung lies in the upper portion of the sleeve/tub that connects the parietal and visceral pleura; in the lower portion (collapsed, known as the pulmonary ligament) is nearly empty except for lymph vessels
- Phrenic nerves lie b/w mediastinal pleura and pericardium, anterior to root of lung
- Descending Aorta and Aortic Arch
- Intercostal Arteries – arise from aorta
- Intercostal Veins – accompany intercostals arteries
- Intercostal Nerves - accompany intercostals vessels, disappears dorsally in innermost intercostal muscle, which connects proximally to the sympathetic trunk
- Sympathetic Trunk are chains of sympathetic ganglia; part of the autonomic nervous system; cervical, thoracic (part visible here), lumbar, and sacral chains; since the trunk lies posterior to the lungs, it is not part of any mediastinal subdivision

SYMPATHETIC NERVE DISTRIBUTION (Fig 1.19)
- preganglionic fibers (thick, whitish, efferent) pass from spinal cord through ventral roots to the spinal nerves; they then pass through white rami communicantes to the ganglia of the sympathetic chain, from there, it can take one of 2 routes:
1. w/o interruption, pass through thoracic splanchnic nerves, and terminate in the prevertebral ganglia (celiac, superior mesenteric) that contain cell bodies of secondary neurons; preganglionic fibers synapse here and the postganglionic fibers of these secondary neurons reach the abdominal and pelvic viscera
2. preganglionic fibers may synapse in the sympathetic ganglia (of chain); the postganglionic fibers (thin/grayish) pass through the gray rami communicantes to the peripheral nerves, these postganglionic supply blood vessels, sweat glands, and smooth muscle fibers of hair follicles
- Sympathetic Trunk (Chain) also contains afferent fibers that carry sensory info form viscera and blood vessels to the CNS
- Greater Splanchnic Nerve, largest of the three splanchnic nerves, it receives contributions from several sympathetic ganglia of the trunk

LUNG
- Cardiac notch is located on the anterior border of the superior lobe of the left lung
- Lingula is most inferior and anterior portion of the left superior lobe
- Lung surfaces: costal, medial, and basal (or diaphragmatic), borders are anterior and inferior

CONTACT IMPRESSIONS
- Cardiac Impression and groove for esophagus are on mediastinal surface of the RIGHT lung; cardiac impression and the continuous groove for aortic arch and descending aorta on the mediastinal surface of the LEFT lung
- at the Hilus various structures (bronchus, pulmonary artery, pulmonary veins) enter and leave the lung; bronchus lies posterior, artery lies superior, and veins lie inferior (BAV counterclockwise = right and clockwise = Left; posterior anterior (superior)  inferior (anterior)
- Main bronchus – two bronchi, right and left
- RIGHT bronchus: 3 lobar branches (superior, middle, inferior); right superior bronchus = eparterial bronchus b/c it is superior to other bronchi and the pulmonary artery
- LEFT bronchus: 2 lobar branches (superior and inferior)
- Segmental Bronchi contain pieces of cartilage; its ramifications go far into lung tissue
- Bronchioles and Arterioles (pulmonary artery) are intrasegmental, w/in same segment
- Bronchioles and Tributaries (pulmonary vein) are intersegmental, in different segments
- Bronchial arteries – nutrient vessels for the lung tissue, also at hilus (lung root)
- Bronchial veins do NOT exist!
- Lymph nodes, lymph vessels, and autonomic nerve fibers also at hilus
- Each lung has 10 bronchopulmonary segments; each one is aerated by a tertiary bronchus and supplied by a single branch of the pulmonary artery

MEDISTINUM (Fig 1.24)
- b/w pleural cavities, extends from superior aperture of the thorax to the diaphragm, and from the sternum anteriorly to the bodies of the 12 thoracic vertebrae posteriorly
- 4 classic anatomical subdivisions of mediastinum: superior, anterior, middle, posterior
- structures traversing the length of the medistinum (esophagus, vagus nerve, phrenic nerve, and thoracic duct) lie, of course, in more than one subdivison
- border b/w superior and rest = horizontal line passing at sternal angle and through intervertebral disc b/w T4 and T5; superior border of fibrous pericardium and level of bifurcation of trachea (superior border of the root of lung)
- Anterior mediastinum is relatively small and unimportant portion b/w sternum and pericardium, thymus might reach inferiorly into this region
- Middle medistinum contains the pericardium with the enclosed heart and roots of the great vessels
- Posterior mediastinum, posterior to pericardium and anterior to the bodies of the lower 8 thoracic vertebrae

MIDDLE MEDIASTINUM AND HEART
- Middle mediastinum contains the pericardium (with adjacent phrenic nerves), the heart, the roots of the great vessels passing to/from the heart
- Pericardium is a sac enclosing the heart and pierced by roots of the 8 vessels: 2 caval veins (SVC & IVC), 2 arteries (pulmonary trunk and aorta), 4 pulmonary veins
- Outer surface (of pericardium) is fibrous and tough
- Inner surface (of pericardium) is serous and smooth; parietal and visceral layers
- Parietal layer of serous pericardium covers inner surface of the fibrous pericardium
- Visceral layer of serous pericardium = epicardium, intimately invests the heart
- Pericardial cavity is a potential space b/w the parietal and visceral layers of serous pericardium
- posteriorly the oblique pericardial sinus is a serous-lined cul-de-sac bounded by IVC and 4 pulmonary veins
- Transverse pericardial sinus is a serous-lined tunnel that runs transversely b/w venous and arterial poles of the heart
- Inferior part of tough, fibrous pericardium is densely attached to the tendinous part of the diaphragm; thus function of heart is influenced by diaphragmatic movements during respiration
- Superior Vena Cava, Ascending Aorta and arch of aorta, Pulmonary Trunk (artery)
- ligamentum arteriosum and recurrent laryngeal nerve (branch off of the left vagus nerve) are located in interval b/w aortic arch and pulmonary trunk
- left vagus nerve passes over the lateral aspect of the aortic arch

HEART AND GREAT VESSELS IN SITU
- Right atrium, Right ventricle (largest part of the anterior surface of the heart), Left atrium, Left ventricle (which is responsible for the apex of the heart)
- Right coronary artery and anterior interventricular branch (LAD, left anterior descending) of the left coronary artery
- Superior to the heart SVC, ascending aorta, left vagus nerve, and the recurrent laryngeal nerve (in relation to ligament arteriosum)
- Coronary or atrioventricular groove (Sulcus) runs obliquely around the heart, separating atria and ventricles; typically filled with fat
- anterior and posterior Interventricular Grooves separate the ventricles from one another and therefore denotes the position of the interventricular septum
- grooves/sulci contain blood vessels

CORONARY ARTERIES
- Coronary arteries originate from the ascending aorta (three aortic valvules/cusps), supply heart with oxygenated blood from the lungs (aorta leaves the left ventricle)
- LEFT coronary artery comes from left coronary cusp: circumflex branch and anterior interventricular (LAD, left anterior descending)
- RIGHT coronary artery comes from the right coronary cusp: atrial branch  sinuatrial (SA) nodal branch, then later marginal branch and posterior interventricular

CORONARY VEINS
- Most veins are tributaries to the coronary sinus, lies in the posterior part of coronary sulcus; opens into the RIGHT atrium
- Two major veins off coronary sinus are Great cardiac vein and Middle cardiac vein

RIGHT ATRIUM (Fig 1.33)
- smooth posterior wall, receives the following veins: SVC, IVC, and coronary sinus
- rough anterior wall, comb-like parallel ridges, the pectinate muscles
- posterior and anterior walls are separated by a vertical ridge, the crista terminalis
- Valve of coronary sinus guards the opening of the coronary sinus that empties into the right atrium (located b/w the opening of the IVC and atrioventricular orifice)
- Atrioventricular or tricupsid orifice leads anteriorly to the ventricle
- Fossa ovalis is an oval depression of the interatrial wall
- fetal foramen ovale remnant; IVC blood went to fossa ovalis and SVC blood went to tricupsid orifice)
- SA (“pacemaker” of the heart, sets the heart rate) and AV nodes are too small to be seen, but important in conduction system

RIGHT VENTRICLE (Fig 1.34)
- cresent-shaped on transverse section (Fig 1.36); interventricular septum is convex on the right atrium, b/c left arterial has higher pressure than the right venous side
- Right atrioventricular orifice, tricupsid valve, is located dorsally and has three cusps
- Three cusps are anterior, septal, and posterior cusps, they’re continuous at their bases
- Chordae tendineae are tendinous strands that pass from the margins and ventricular surfaces of the cusps into the apices of the papillary muscles
- Papillary muscles – anterior, posterior, and septal; control adjacent sides of cusps
- Anterior papillary muscle is the largest and the most prominent; its chordae are attached to anterior and posterior cusps
- Posterior and septal papillary muscles are smaller and more irregular
- Traceculae Carnae are muscular ridges and bridges that roughen the wall of the right ventricle
- Septomarginal trabecula (moderator band) stretches from the interventricular septum to the base of the anterior papillary muscle
- The conus arteriosus or Infundibulum is the cone shaped portion of the chamber inferior to the pulmonary orifice, the orifice of the pulmonary trunk (artery)
- Within the right ventricle, the blood takes a U-shaped course passing from the orifice of entrance (interventricular, tricuspid) to the orifice of exit (pulmonary)
- Valve of the pulmonary trunk (pulmonary valve) consists of 3 semilunar valvules of cusps: an anterior, a right, and a left
-

LEFT ATRIUM
- 4 pulmonary veins enter into right and left sides of the atrium
- left atrioventricular or mitral valve (or bicuspid: anterior and posterior) opens through inferior half of the anterior wall into the left ventricle
- tubular left auricle?
- site of closure of the foramen ovale (corresponds to the fossa ovalis in the right atrium)
- smooth atrial wall, except for pectinate muscles in the left auricle

LEFT VENTRICLE (Fig 1.35)
- cone shaped in outline and circular on cross section (Fig 1.36)
- muscular wall is approx. 1 to 1.5 cm thick (3x thickness of the right ventricle)
- left atrioventricular or mitral valve or bicuspid contain anterior and posterior cusps; larger anterior intervenes b/w the atrioventricular and aortic orifices
- Chordae tendineae are attached to two papillary muscles, anterior and posterior
- trabeculae carneae (see right ventricle)
- Aortic valve has three semilunar cusps: right, left, and posterior (noncoronary) cusps, nodule (small fibrous thickening at the middle of the free margin of each cusp)
- Coronary arteries off of the aorta (supply heart with oxygenated blood)
- thick and extensive muscular part of the interventricular septum and membraneous part of the interventricular septum, just inferior to the attached margins of the right coronary and noncoronary cusps of the aortic valve
- Q: What happens if the ligamentum arteriosum fails to close postnatally? (pg. 27)
- A: ???

POSTERIOR MEDIASTINUM
- anterior to the bodies of the eight thoracic vertebrae (T5 to T12) and posterior to the pericardium; the esophagus, descending aorta, and mediastinal portions of the lungs are closely related to the pericardial sac (esophagus lies posterior to left atrium and to part of the left ventricle)
- Esophagus (collapsed muscular tube) is located anterior and to the right
- Vagal nerves (left and right vagus nerves)
- Right vagus nerve (posterior to right lung) separates and spreads out on the esophagus as the esophageal plexus (Fig 1.38)
- Left vagus nerve crosses the left side of the aortic arch, courses posteriorly to root of the left lung and then onto the esophagus
- left recurrent laryngeal nerve (a branch of left vagus) courses immediately posterior to the ligamentum arteriosum
- the bundles of the esophagneal plexus combine to form the two vagal trunks, left becomes anterior vagal trunk and right becomes posterior vagal trunk (due to gut rotation during development); they travel through diaphragm with esophagus and supply stomach and other parts of the intestinal tract
- Azygos system of veins (branches over the right superior bronchus prior to draining into SVC); right intercostal veins (from VAN) are tributaries to azygos vein
- Cross channels (irregular) bring blood from left side via hemiazygos veins
- Thoracic duct is thin-walled, pale, easily torn structure located posterior to esophagus and b/w descending aorta and azygos vein; traverses the diaphragm together with the descending aorta
- Descending aorta: arterial branches (to esophagus and trachea), posterior intercostals branches, bronchial arteries
- Thoracic Greater Splanchnic nerve on right and left (formed from fibers of the 5th to 10th thoracic sympathetic ganglia) of descending aorta
- Lesser Splanchnic Nerve is formed by fibers from 10th and 11th thoracic sympathetic ganglia; both greater and lesser pierce the diaphragm (and course in abdomen)

SUPERIOR MEDIASTINUM
BOUNDARIES
- Superior: superior aperture of thorax
- Posterior: thoracic vertebrae T1 - T4
- Anterior: manubrium of the sternum
- Lateral: mediastinal pleurae of the two lungs
- Inferior: plane of sternal angle to intervertebral disc T4-T5, superior to pericardium

THYMUS AND GREAT VEINS
- Thymus is a functionally inactive fatty mass in the cadaver, lies posterior to the manubrium, note its venous drain
- Brachiocephalic veins (innominate veins) meet to form the SVC at right margin of manubrium; left lies posterior to thymus

ARCH OF AORTA AND BRANCHES
- Aortic arch begins and ends at same level, anteriorly at sternal angle and posteriorly at intervertebral disc T4 – T5, passes anterior to posterior; arches superior to (over) left main bronchus and then becomes the descending aorta
- Brachiocephalic trunk (innominate artery) arises from the summit of the aortic arch
- Left common carotid artery branches off b/w innominate and subclavian branches
- Left subclavian artery lies immediately posterior to the left common carotid artery
- Concavity of the aortic arch is connected to the left pulmonary artery by a stout, obliquely set cord, the ligamentum arteriosum
- Internal jugular vein and subclavian vein meet to form right brachiocephalic vein, which joins left brachiocephalic vein to form Superior Vena Cava (SVC)
- the following structures are closely related to aortic arch: left pulmonary artery, ligamentum arteriosum, left recurrent laryngeal nerve, and left main bronchus (w/ lymph nodes) and esophagus
- Cardiac nerves cross the aortic arch, but are hard to visualize; they also contain sensory fibers that carry the sensation of pain (pg. 31)

LEFT PHRENIC NERVE AND LEFT VAGUS
- Aortic arch is crossed by two nerves (left phrenic nerve and left vagus nerve) that descend vertically from neck into throax
- Left phrenic nerve crosses the aortic arch, is located b/w subclavian artery and subclavian vein, goes anteriorly to the root of the lung, enters into diaphargm
- Left vagus nerve located in the angular interval b/w subclavian and the left common carotid arteries; goes to the left side of the aortic arch; descends to the esophagus, ie passes posterior to the left main bronchus
- Left recurrent laryngeal nerve is immediately posterior to ligamentum arteriosum

RIGHT PHRENIC NERVE AND RIGHT VAGUS
- Right phrenic nerve descends lateral to the SVC, anterior to the root of the right lung, lateral to the pericardial sac, and lateral to the IVC (Fig 1.39)
- Right vagus nerve runs along the right side of the trachea and toward posterior aspect of the root of the right lung (Fig 1.41), small branches of the vagus cross the trachea anteriorly ; these are cardiac branches on their way to the deep cardiac plexus (?)

TRACHEA AND RELATED STRUCTURES
- Tracheobronchial lymph nodes, mass of pigmented nodes, are on both sides of the trachea and in the vicinity of the its bifurcation and fill the angle w/in the fork of the trachea and intervenes b/w the right pulmonary artery and the esophagus
- Bifurcation of the trachea and the four major structures topographically related (deep  superficial): lymph nodes  pulmonary arteries  ascending aorta and aortic arch  brachiocephalic veins (form the SVC)
- Tracheal “rings” are imperfect; anterior 2/3 consists of cartilage, the posterior 1/3 is musculofibrous membrane
- Carina is a ridge on the inside of the tracheal bifurcation; slightly left of median plane
- Right main bronchus is more vertical, shorter, and wider than the left one