Thorax Combined

Bones of the Thorax

• A prominent feature of each thoracic vertebra is the thick body, which is weight bearing
• On the lateral surfaces of each vertebral body are facets for the articulation of the heads of the ribs
• The head of rib 5 articulates with a facet on the superior and lateral surface of the body of T5 as well as to a facet on the inferior and lateral surface of T4; the joint of the head of the rib
• The neck of each non-floating rib articulates with the transverse process of the corresponding vertebrae at the costotransverse joint
• Costotransverse joints are synovial plane joints that permit gliding of the articular surfaces
• Rib elevation and depression is permitted with each breath due to gliding of articular surfaces
• The way the ribs articulate with the sternum and vertebral column helps the diaphragm increase/decrease thoracic volume during inspiration/expiration

Sternum

• The sternum has 3 parts: the manubrium, body, and xiphoid process
• The manubrium lies at the level of the third and fourth thoracic vertebrae (T3 and T4)
• Along the superior margin of the manubrium is the suprasternal or jugular notch
• Both the clavicle and the first rib articulate with the manubrium
• The joint between the manubrium and the body is the manubriosternal joint, which forms the sternal angle
• The sternal angle is an important landmark for the level of the disc between T4 and T5 and is also the level of the second rib
• The manubriosternal joint tends to be fused in older people
• The xiphoid process is cartilaginous in younger people and ossified in older people

Ribs

• There are 12 pairs of ribs; each rib articulates posteriorly with two thoracic vertebrae via the costovertebral joint
• An exception to the rule that each rib articulates posteriorly with two thoracic vertebrae via the costovertebral joint is the first rib, which articulates with the first thoracic vertebra only
• The parts of a typical rib include the head, tubercle, neck, shaft, and costal groove
• The head of a typical rib has two articular facets for adjacent vertebral bodies
• The tubercle of a typical rib articulates with a transverse costal facet
• The costal groove contains intercostal nerves and vessels
• The first 7 (sometimes 8) ribs are considered true ribs
• Ribs 8 (usually), 9, and 10 are false ribs because they are attached to the rib found just superior, and not directly to the sternum
• Ribs 11 and 12 are floating ribs because they are suspended in abdominal musculature
• Located at the inferior margin of most ribs is the costal groove, which helps protect the intercostal nerve and vessels
• The ribs are attached to the sternum (sternocostal joints) or to each other (interchondral joints) by costal cartilage

Muscles of the Thoracic Wall

• The interval between each rib typically contains three layers of muscles
• The outer layer of muscles between each rib is the external intercostal muscle which elevates the ribs during inspiration
• Deep to the external intercostal muscle lies the internal intercostal muscle
• The third layer of muscle between each rib is the innermost intercostal muscle and is patchy
• Between the internal intercostal muscle layer and the innermost intercostal muscles (if present) are the intercostal vein, artery and nerve
• The intercostal vein, artery and nerve are usually running near the inferior margin of the rib, either in or near the costal groove

Diaphragm

• A musculotendinous structure that separates the thoracic and abdominal cavities
• Attached to the inferior ribs, and the thoracic vertebrae
• It descends during inspiration, increasing the superior-inferior dimension of the thoracic cavity
• Innervated by the phrenic nerve

Innervation of the Thoracic Wall

• The spinal nerves exit the vertebral column through the intervertebral foramina
• Each spinal nerve divides into a dorsal primary ramus and a ventral primary ramus
• Dorsal primary rami carries afferent sensory fibers from the skin and joints of the back, and efferent motor fibers to muscles of the back
• In the thorax (T1-T11), the ventral primary rami become the intercostal nerves (T12 becomes the subcostal nerve) that run along the inferior margin of each rib in the intercostal space
• The intercostal nerves supply the muscles listed above and are also sensory to the strip of skin overlying each intercostal space
• The pattern of cutaneous sensation supplied by a spinal nerve from a single spinal cord level is called a dermatome

Vasculature of the Thoracic Wall

• Supplied by the posterior intercostal arteries and the anterior intercostal arteries
• The posterior intercostal arteries are branches of the aorta and follow the intercostal nerves in the intercostal spaces
• The anterior intercostal arteries are branches of the internal thoracic arteries
• The anterior intercostal arteries run laterally and eventually anastomose with the posterior intercostal arteries
• The anterior intercostal arteries supply the breasts as well as the muscles and fascia of the anterior thorax
• The internal thoracic arteries run on either side of the sternum along the inner surface of the thoracic wall
• The internal thoracic arteries continue into the abdominal wall as the superior epigastric arteries and are branches of the subclavian arteries

Breast

• In females, the mammary glands develop between the pectoralis major muscle (and parts of the serratus anterior muscle) and the skin
• There is also a wing-like lateral projection of mammary gland called the axillary tail
• In non-lactating women, the glands themselves and the lactiferous ducts that drain the glands are quite small
• Most of the volume of the breast is instead occupied by fat and the suspensory ligaments that anchor the breast to underlying deep fascia
• Superficial fascia is a term used by anatomists to describe the layer of fat and connective tissue just beneath the skin
• Deep fascia is the tough sheet of connective tissue that surrounds muscles
• Most of the breast's lymphatics drain into the axillary lymph nodes

Pleura and Pleural Cavities

• The pleural sacs are the double layers of membrane that surround each lung
• The inner layer closely enveloping the lung is the visceral pleura; the outer layer is the parietal pleura
• The thin space between the pleural membranes is the pleural cavity, which is filled with a layer of pleural fluid
• The pleurae reduce friction during respiration
• The pleural cavity is a potential space
• There is negative pressure in the pleural cavity, creating an outward pull on the lungs that keeps them inflated
• Normally the two layers of the pleura are closely opposed
• If air enters the pleural cavity either spontaneously or as the result of trauma, the lung will collapse
• The visceral pleura is insensitive to pain, but the parietal pleura is richly innervated
• The central part of the diaphragmatic pleura and the mediastinal pleura, respectively, are innervated by branches of the phrenic nerve (formed from the ventral primary rami of C3, C4, and C5)
• The costal pleura is innervated by branches of the intercostal nerves

Lungs

• The lungs are the organs of respiration.
• While living, the lungs are light and flexible, and will readily collapse to about one-third of their normal size if not inflated.
• In the cadaver, the lungs are firm and have the impressions of surrounding structures, especially on their mediastinal surface.
• Each lung has an apex, base, root, and hilum.
• The root is the bundle of structures that enter and leave the lung; they do so at a point called the hilum.
• The left lung is usually divided into a superior lobe and an inferior lobe by the oblique fissure.
• The right lung is usually divided into a superior, middle and inferior lobe by a horizontal fissure and an oblique fissure.
• Fissures may be incomplete or partly fused.
• The left lung has a distinctive cardiac notch in its anterior margin

Roots, Bronchi and Blood Supply

• The root is the bundle of structures entering or leaving the lung at the hilum
• Hilum also refers to the pit-like depression on a fruit where the stem was attached
• The roots contain the primary bronchi and pulmonary vessels, connective tissue, nerves, and lymphatics
• The primary bronchi branch regularly after entering the hilum, sending a secondary bronchus to each lobe
• The secondary bronchi in turn divide into tertiary bronchi, which supply specific regions of the lungs
• Blood from the right ventricle is pumped through the right and left pulmonary arteries to each lung via the root
• Branches of the pulmonary arteries are closely associated with the bronchi
• The pulmonary veins are paired as they leave the hilum: a superior pulmonary vein and inferior pulmonary vein exit each lung and enter the left atrium

Innervation of the Lungs

• The lungs receive parasympathetic innervation via the vagus nerve (CN X)
• Parasympathetic fibers are motor to the smooth muscles of the bronchi (bronchoconstrictors), inhibitory to the muscles of blood vessel walls (vasodilators), and cause the glands of the bronchi to secrete fluid and mucus
• Sympathetic innervation to the lungs (from the sympathetic chain) inhibits bronchiolar smooth muscle contraction (bronchodilators) and the secretion of pulmonary glands, and is motor to pulmonary vasculature (vasoconstrictors)

Pericardium

• A double-walled fibrous sac that encloses the heart and the roots of the great vessels
• It occupies most of the middle mediastinum, and functions to maintain the position of the heart and protect it from overfilling
• It has two parts: the fibrous layer (a tough fibrous layer closed by attachment to the great vessels; it blends with the central tendon of the diaphragm), and a serous layer (a smooth inner sac with lubricated surfaces that allow movement)
• The serous layer contains a parietal layer (lines the inner surface of the fibrous pericardium), the visceral layer (covers the entire surface of the heart), and the pericardial cavity (the potential space between the parietal and visceral layers)
• Pericarditis is inflammation of the pericardium that causes substernal pain and produces pericardial effusion
• Cardiac Tamponade causes effusion that impairs cardiac filling, resulting in circulatory failure but can be treated by pericardiocentesis

Heart

• Has an apex, a base, and four surfaces: sternocostal, diaphragmatic, left pulmonary and right pulmonary

• The base is located posteriorly and formed mainly by the left atrium

• Contains a Right atrium (receives venous blood from the superior vena cava (SVC), inferior vena cava (IVC), and coronary sinus), coronary sinus(returns much of the venous blood from the heart itself to the right atrium and lies in the posterior part of the coronary groove), auricle(blind pocket, overlying the ascending aorta), pectinate muscle(ridges of muscles are located in the inner walls of both atria), and interatrial septum(contains the fossa ovalis which is an oval depression where the septum is thin and is the site of the foramen ovale in the fetus)

• Atrial septal defect (ASD) can allow blood to shunt from the left to the right side of the heart

• The left atrium forms most of the base of the heart, receives the openings of the 4 pulmonary veins from the lungs, contains the left auricle(forms the superior part of the left border of the heart)

• Thrombi (blood clots) can form on the walls of the left atrium in certain types of heart disease

• In the ventricles, trabeculae carneae are irregular bundles of muscle projecting on the inner surface which affect structural support and compliance and atrioventricular (AV) valves (right AV valve = tricuspid valve and left AV valve = bicuspid (mitral) valve)

• Semilunar valves are aortic and pulmonary

• The right ventricle forms most of the anterior surface, and almost all of the inferior border -Right atrioventricular (tricuspid) valve contains cusps, papillary muscles and chordae tendineae

• -- Cusps: 3 fibrous cusps are attached to the annulus fibrosis

• -- Papillary Muscles: Conical projections into cavity

• -- Chordae Tendineae: Small tendinous bands that connect the valve cusps to the papillary muscles

• Clinical Condition: pulmonary valve stenosis

• Interventricular septum corresponds to interventricular grooves on the surface.

• -- Membranous part: thin upper part near atrium.

• -- Muscular part: thick, major part

• Ventricular septal defect (VSD) is the most common congenital heart defect,

• the wall is 2-3 times thicker because the left ventricle contracts against greater resistance than the RV

• Two large sets of papillary muscles attach to the cusps via chordae tendineae in the left atrioventricular (bicuspid or mitral) valve

• -- The mitral valve is the most frequently diseased of the heart valves.

• The aortic valve is 3 semilunar cusps and located in the right posterosuperior part of the LV

Auscultation of Heart Sounds

• Mitral Valve: Apex (5th intercostal space near the mid-clavicular line)
• Pulmonary Valve:Left 2nd intercostal space
• Tricuspid Valve: lower left sternal border
• Aortic Valve: right 2nd intercostal space

Blood Supply

• Right coronary artery—originates in the right aortic sinus, runs in the coronary sulcus to the back of the heart where it gives off the posterior interventricular artery, which anastomoses with the anterior interventricular branch of the left coronary artery.
• The branches goes to the right atrium, right ventricle, and interventricular septum
• Sinoatrial nodal artery is the most common site of origin (60%)
• Right marginal branch─runs toward the apex of the heart
• 85% of the cases the right coronary supplies the AV node
• Left coronary artery (and branches)—arises from the left aortic sinus and gives off a circumflex branch and the anterior interventricular artery and supplies most of the LV, LA, interventricular septum, and some of the RV.
• Venous drainage: anterior cardiac veins drain directly into the right atrium and the coronary sinus; receives most veins of the heart and runs in the posterior part of the coronary groove and ends in the right atrium and receives the great cardiac vein, middle cardiac vein and the small cardiac vein

Clinical Conditions and Conduction System

• Although the coronary arteries anastomose with each other at the arteriolar level, they are functional end arteries where a sudden block leads to necrosis of the cardiac muscle (myocardial infarction)
• Coronary arteriosclerosis results in slow narrowing of the lumen of these arteries
• Angina pectoris is a clinical syndrome characterized by substernal discomfort resulting from myocardial ischemia
• A surgical treatment for severe coronary arteriosclerosis is a coronary artery bypass graft (CABG)
• Autonomic and sensory fibers go from the vagus nerve and sympathetic trunk via the cardiac plexus
• The sympathetic supply arises from the cervical and upper thoracic part of the sympathetic trunk.
• Postganglionic sympathetic fibers terminate on the SA and AV nodes, and on the coronary arteries and stimulation of the sympathetic nerves increases the heart rate and contractility while parasympathetic fibers also terminate on the SA and AV nodes and coronary arteries
• Referred cardiac pain is usually to left shoulder, and medial side of left arm, forearm and hand is mediated by afferent nerves in the cardiac branches of the sympathetic trunk where these afferents enter the T1-T4 spinal nerves, resulting in pain referred to these dermatomes
• Referred cardiac pain in women can be different from men because women are more likely to experience microvascular coronary disease, affecting smaller arteries in the heart, leading to a wider range of symptoms
• The conducting system consists of specialized muscle fibers and conducting fibers, which are not nervous tissue that conducts impulses that connect certain pacemaker regions of the heart with cardiac muscle fibers where both atria contract together as do the ventricles, but atria contract first:
  • Sinoatrial (SA) node: natural pacemaker of the heart and is the location is the junction of superior vena cava and right atrium; the impulse for contraction begins at the SA node and is conducted throughout the atria by ordinary atrial myocardial fibers, arriving at the AV node -Atrioventricular (AV) node: location above the opening of the coronary sinus in the atrial septum, and an Atrioventricular bundle passes from the AV node, divides into right & left bundle branches that carry the depolarization to the apices of the right and left ventricles, where the rest of the ventricular myocardium is depolarized by the continued branching of the conduction bundles known as Purkinje fibers
• Pacemakers are used to correct arrhythmias, abnormalities in cardiac conduction rhythms
• The passage of impulses over the heart can be amplified and recorded as an electrocardiogram (ECG or EKG)

Mediastinum

• The space between the two pleural sacs extends from the sternum to the vertebral column and contains structures within the thoracic cavity except the lungs and pleura
• Subdivisions: superior mediastinum from superior thoracic aperture to sternal angle (inferior border of T4) and the inferior mediastinum which is from the sternal angle to the diaphragm anterior mediastinum is anterior to heart and pericardium, middle mediastinum is pericardium and heart, with the posterior mediastinum being posterior to pericardium and diaphragm

Superior Mediastinum

• Anterior to posterior in this area:
  • Begins with the thymus
    • Involved in the development of the immune system, situated posterior to the manubrium, involutes during puberty, and thymoma is a clinical condition to be worried about
  • Followed by the great vessels which is formed posterior to medial end of clavicle by joining the internal jugular vein (IJV) and subclavian vein
  • The vessels will join to form the superior vena cava near the right 1st costal cartilage that enters the right atrium (RA) in the middle mediastinum
  • The arch of the aorta arches posterosuperior and to the left, anterior to the trachea, then passes inferiorly adjacent to vertebral column while giving off 3 branches: the brachiocephalic trunk, left common carotid artery and left subclavian artery
  • The pulmonary trunk branches into the right and left pulmonary arteries
• Nerves found here are:
  • Vagus nerve: the sole motor supply to the diaphragm as well as sensory to the pericardium, pleura, parietal peritoneum, and diaphragm
  • Phrenic Nerve: passes anterior to the root of the lung, along the pericardium to enter the diaphragm

Posterior Mediastinum

• The following structures are located in posterior mediastinum
• Thoracic (descending) aorta: descends along the left side of the vertebral column that penetrates the diaphragm at T12 (aortic hiatus) along with the thoracic duct and the azygos vein
• Thoracic duct: ascends through the posterior mediastinum between the aorta and the azygos vein, then crosses posterior to the esophagus to empty into the junction of the left internal jugular and subclavian veins
  • Receives all lymph/fluid from the left side of the head, neck and thorax, the left upper limb, and the entire body below the diaphragm
  • Returns excess interstitial fluid to the venous system and transports fat absorbed from the GI tract back to the venous system
• Azygos vein: interconnects the superior and inferior vena cava while draining the posterior thoracic and abdominal wall and the back
  • Ascends in posterior mediastinum to the right of the vertebral column, then arches over the root of the right lung to join the superior vena cava
• Esophagus: descends posterior to the left atrium and is constrained in three regions
  • Superiorly towards the arch of the aorta and the region where it crossed by the left mainstem bronchus, inferiorly at the esophageal hiatus
• Sympathetic trunks: along the lateral sides of the thoracic vertebrae that give rise to the thoracic splanchnic nerves, which pass through the diaphragm into the abdomen.