HTMS SELF ASSESSMENT HIGH YIELD ANATOMY (THORAX).

THORAX

Thoracic Wall

I. Skeleton of the Thorax

II. Articulations of the Thorax

III. Breasts and Mammary Glands

IV. Muscles of the Thoracic Wall

V. Nerves and Blood Vessels of the Thoracic Wall

VI. Lymphatic Drainage of the Thorax

VII. Thymus

VIII. Diaphragm and Its Openings

Mediastinum, Pleura, and Organs of Respiration

I. Mediastinum

II. Trachea and Bronchi

III. Pleurae and Pleural Cavities

IV. Lungs

V. Respiration

VI. Lymphatic Vessels of the Lung

VII. Blood Vessels of the Lung

VIII. Nerve Supply to the Lung

IX. Development of the Respiratory System

Pericardium and Heart

I. Pericardium

II. Heart

III. Great Vessels

IV. Development of the Heart

V. Development of the Arterial System

VI. Development of the Venous System

VII. Fetal Circulation

Structures in the Posterior Mediastinum

I. Esophagus

II. Blood Vessels and Lymphatic Vessels

III. Autonomic Nervous System in the Thorax

HIGH YIELD

The sternum can be used for bone marrow biopsy because of its accessible location and it possesses

hematopoietic marrow throughout life.

■ The sternal angle (of Louis) is the junction between the manubrium and body of the sternum located at the level where (1) the second ribs articulate with the sternum, (2) the aortic arch begins and ends, (3) the trachea bifurcates into the right and left primary bronchi, and (4) it marks the plane of separation between the superior and inferior mediastinum.

■ The true ribs are the first seven ribs (ribs 1–7), the false ribs are the lower five ribs (ribs 8–12), and the floating ribs are the last two ribs (ribs 11 and 12).

■ Flail chest occurs when a segment of the anterior or lateral thoracic wall moves freely because of multiple rib fractures, allowing the loose segment to move inward on inspiration and outward on expiration.

■ Muscles of inspiration include the diaphragm, external, internal (interchondral part), and innermost intercostal muscles, sternocleidomastoid, levator costarum, serratus anterior, serratus posterior superior, scalenus, and pectoral muscles.

■ Muscles of expiration include anterior abdominal, internal intercostal (costal part), and serratus posterior inferior muscles. Quiet inspiration results from contraction of the diaphragm, whereas quiet expiration is a passive process caused by the elastic recoil of the lungs.

■ The trachea begins at the inferior border of the cricoid cartilage (C6) and has 16 to 20 incomplete hyaline cartilaginous rings that prevent the trachea from collapsing and that open posteriorly toward the esophagus. It bifurcates into right and left primary bronchi at the level of the sternal angle.

■ The carina, the last tracheal cartilage, separates the openings of the right and left primary bronchi. The right primary bronchus is shorter, wider, and more vertical than the left and divides into the superior (eparterial), middle, and inferior secondary (lobar) bronchi. The left primary bronchus divides into the superior and inferior lobar bronchi.

■ The bronchopulmonary segment is the anatomical, functional, and surgical unit of the lungs and consists of a segmental (tertiary or lobular) bronchus, a segmental branch of the pulmonary artery, and a segment of lung tissue, surrounded by a delicate connective tissue (intersegmental) septum. The pulmonary veins are intersegmental.

■ Bronchopulmonary (hilum) nodes drain into tracheobronchial nodes, then to paratracheal nodes, and eventually to the thoracic duct.

■ Lung buds arises from the laryngotracheal diverticulum in the embryonic foregut region.

■ Lungs are the essential organs of respiration. The right lung is divided into the upper, middle, and lower lobes by the oblique and horizontal fissures. The left lung is divided into the upper and lower lobes by an oblique fissure and contains the lingula and the cardiac notch.

■ Most abscesses occur in the right lung, because the right main bronchus is wider, shorter, and more vertical than the left, and thus aspirated infective agents gain easier access to the right lung.

■ The cupula is the dome of cervical parietal pleura over the apex of the lung. It lies above the first rib and is vulnerable to trauma at the root of the neck.

■ Pancoast tumor (superior pulmonary sulcus tumor) is a malignant neoplasm of the lung apex which may cause a lower trunk brachial plexopathy and a lesion of cervical sympathetic chain ganglia with Horner syndrome (ptosis, enophthalmos, miosis, anhidrosis, and vasodilation).

■ Chronic obstructive pulmonary disease (COPD) is an obstruction of airflow through the airways and lungs and includes chronic bronchitis and emphysema. Shortness of breath in COPD occur when the walls of airways and air sacs get inflamed, destroyed, lose elasticity, and hypersecrete mucus.

■ Chronic bronchitis is an inflammation of the airways, which results in excessive mucus production that plugs up the airways, causing a cough and dyspnea (difficulty in breathing).

■ Emphysema is an accumulation of trapped air in the alveolar sacs, resulting in destruction of the alveolar walls, reducing the surface area for gas exchange.

■ Asthma is an airway obstruction and is characterized by dyspnea, cough, and wheezing with spasmodic contraction of smooth muscles in the bronchi and bronchioles, narrowing the airways.

■ Barrel chest is a chest resembling the shape of a barrel because the lungs are overinflated and the thoracic cage becomes enlarged, as seen in cases of emphysema or asthma.

■ Bronchiectasis is a chronic dilation of bronchi and bronchioles, resulting from destruction of bronchial elastic and muscular elements, which may cause collapse of the bronchioles. It may be caused by pulmonary infections or by a bronchial obstruction with heavy sputum production.

■ Pleurisy (pleuritis) is inflammation of the pleura with exudation (escape of fluid from blood vessels) into its cavity, causing the pleural surfaces to be roughened, producing friction.

■ Pneumothorax is an accumulation of air in the pleural cavity because of an injury to the thoracic wall or the lung, causing no negative pressure in the chest and thus the lung collapses. Tension pneumothorax is a life-threatening pneumothorax in which air enters during inspiration and is trapped during expiration; therefore, the resultant increased pressure displaces the mediastinum to the opposite side, with consequent cardiopulmonary impairment.

■ Pleural effusion is an abnormal accumulation of excess fluid in the pleural space, having two types; the transudate (clear watery fluid) and the exudate (cloudy viscous fluid).

■ Thoracentesis (pleuracentesis or pleural tap) is a surgical procedure to collect pleural effusion for analysis. A needle or tube is inserted through thoracic wall into the pleural cavity posterior to the midaxillary line one or two intercostal spaces below the fluid level but not below the ninth intercostal space. Fluid in the pleural cavity includes hydrothorax (water), hemothorax (blood), chylothorax (lymph), and pyothorax (pus).

■ Pneumonia (pneumonitis) is an infection in the lungs, which is of bacterial, viral, or mycoplasmal origin.

■ Tuberculosis (TB) is an infectious lung disease caused by the bacterium Mycobacterium tuberculosis and is characterized by the formation of tubercles that can undergo necrosis.

■ Cystic fibrosis (CF) is an inherited multisystem disease that has widespread dysfunction of the exocrine glands and pulmonary and gastrointestinal tracts. CF affects the respiratory system by causing an excess production of viscous mucus, obstructing the respiratory airway.

■ Pulmonary edema involves fluid accumulation in the lungs caused by lung toxins. As pressure in the pulmonary veins rises, fluid is pushed into the alveoli and becomes a barrier to normal oxygen exchange, resulting in shortness of breath, increased heart rate, and cough.

■ Atelectasis is the collapse of a lung by blockage of the air passages, pressure on the outside of the lung, or shallow breathing. It is caused by mucus secretions that plug the airway, foreign bodies in the airway, and tumors that compress or obstruct the airway.

Lung cancer has two types, small cell and non–small cell carcinomas. Small cell carcinoma accounts for 20% and grow aggressively, while non–small cell carcinoma (80%) is further divided into squamous cell carcinoma (most common type), adenocarcinoma, and bronchoalveolar large cell carcinoma.

■ Pulmonary embolism is an obstruction of the pulmonary artery or one of its branches by an embolus (air, blood clot, fat, tumor cells, or other foreign material). Its most common origin is deep leg veins (especially those in the calf ).

■ Phrenic nerve supplies somatic motor fibers to the diaphragm. The central part of diaphragm receives sensory fibers from the phrenic nerve, whereas the peripheral part receives sensory fibers from the intercostal nerves.

■ Phrenic nerve lesion may not produce complete paralysis of the corresponding half of the diaphragm because the accessory phrenic nerve usually joins the phrenic nerve in the root of the neck.

■ Pain from an infection of the pericardium (pericarditis) is carried in the phrenic nerve.

■ Pericarditis is an inflammation of the pericardium, and the typical sign is pericardial murmur or pericardial friction rub. Pericarditis may result in pericardial effusion and cardiac tamponade.

■ Pericardial effusion is an accumulation of fluid in the pericardial space, resulting from inflammation caused by acute pericarditis. The accumulated fluid compresses the heart, inhibiting cardiac filling. A radiograph will reveal an enlarged cardiac silhouette with a water bottle appearance.

■ Cardiac tamponade is an acute compression of the heart caused by a rapid accumulation of fluid or blood in the pericardial cavity and can be treated by pericardiocentesis.

■ Pericardiocentesis is a surgical puncture of the pericardial cavity for the aspiration of fluid. A needle is inserted into the pericardial cavity through the fifth intercostal space left of the sternum.

■ The crista terminalis is a vertical muscular ridge running anteriorly along the right atrial wall from the opening of the SVC to the opening of the IVC, providing the origin of the pectinate muscles. It presents the junction between the primitive sinus venosus and the right atrium proper and is indicated externally by the sulcus terminalis.

■ The left atrium is smaller with thicker walls than the right atrium and is the most posterior of the four chambers. The left ventricle forms the heart’s apex, performs harder work, has a thicker wall, and is more conical-shaped than the right ventricle.

■ The papillary muscles contract to tighten the chordae tendineae, preventing eversion of the AV valve cusps into the atrium, thus preventing regurgitation of ventricular blood into the atrium.

■ The septomarginal trabecula (moderator band) is an isolated band of trabeculae carneae that forms a bridge between the interventricular septum and the base of the anterior papillary muscle of the right ventricle. It carries the right limb (Purkinje fibers) of the AV bundle.

■ Atrial septal defect (ASD) is a congenital defect in the interatrial septum due to failure of the foramen primum or secundum to close normally, resulting in a patent foramen ovale. This defect shunts blood from the left atrium to the right atrium, thus mixing oxygenated and deoxygenated blood. A large ASD can cause hypertrophy of the right chambers and pulmonary trunk.

■ Ventricular septal defect (VSD) occurs usually in the membranous part of the interventricular septum and is the most common congenital heart defect. The defect results in left-to-right shunting of blood through the IV foramen, increases blood flow to the lung, and causes pulmonary hypertension.

■ The first (“lub”) sound is caused by closure of the tricuspid and mitral valves at the onset of ventricular systole. The second (“dub”) sound is caused by closure of the aortic and pulmonary valves and vibration of walls of the heart and major vessels at the onset of ventricular diastole.

■ For cardiac auscultation, the stethoscope should be placed over the mitral valve area, in the left fifth intercostal space over the apex of the heart to hear the first heart sound (“lub”).

■ The tricuspid (right AV) valve is most audible over the right or left lower part of the body of the sternum, whereas the bicuspid or mitral (left AV) valve is most audible over the apical region of the heart in the left fifth intercostal space at the midclavicular line. The pulmonary valve is most audible over the left second intercostal space just lateral to the sternum, whereas the aortic valve is most audible over the right second intercostal space just lateral to the sternum.

■ Mitral valve stenosis is a narrowing of the orifice of the mitral valve. This impedes the flow of blood from the left atrium to the left ventricle, causing an enlargement of the left atrium and pulmonary edema due to increased left atrial pressure.

■ Mitral valve prolapse is a condition in which the valve everts into the left atrium when the left ventricle contacts and may produce chest pain, shortness of breath, and cardiac arrhythmia. The SA node (pacemaker) initiates the heartbeat. Impulse travels from the SA node to the AV node to the AV bundle (of His) that divides to right and left bundle branches, then to subendocardial Purkinje fibers, and the ventricular musculature. SA node is supplied by SA nodal branch of the

right coronary artery.

■ Myocardial infarction (MI) is necrosis of the myocardium due to local ischemia. Causes of ischemia include vasospasm or obstruction of the blood supply, most commonly by a thrombus or embolus in the coronary arteries. Major causes of MI include coronary atherosclerosis and thrombosis, and the left anterior descending is the most common site (40%–50%). MI symptoms range from none (silent MI) to severe chest pain or pressure for a prolonged period.

■ Angina pectoris is characterized by chest pain originating in the heart and felt beneath the sternum, in many cases radiating to the left shoulder and down the arm. It is caused by an insufficient supply of oxygen to the heart muscle. It can be treated with nitroglycerin.

■ Endocarditis is an infection of the endocardium of the heart, most commonly involving the heart valves and is caused by a cluster of bacteria on the valves. The valves have reduced defense mechanisms because they do not receive dedicated blood supply, thus immune cells cannot enter. Valve infections can cause cardiac murmur, which is a characteristic sound generated by turbulence of blood flow through an orifice of the heart.

■ Damage to the conducting system interferes with the spread of electrical signals through the heart (heart block). A delay or disruption of the electrical signals produces an irregular and slower heartbeat, reducing the heart’s efficiency in maintaining adequate circulation. Severe heart block requires implantation of a pacemaker.

■ Atrial or ventricular fibrillation is a cardiac arrhythmia resulting from rapid irregular uncoordinated contractions of the atrial or ventricular muscle. Fibrillation causes palpitations, shortness of breath, angina, fatigue, congestive heart failure, and sudden cardiac death.

■ Coronary atherosclerosis is characterized by presence of sclerotic plagues containing cholesterol and lipid material that impairs myocardial blood flow, leading to ischemia and myocardial infarction.

■ Coronary angioplasty is an angiographic reconstruction of a blood vessel made by enlarging a narrowed coronary arterial lumen. It is performed by peripheral introduction of a balloon-tip catheter and dilation of the arterial lumen on withdrawal of the inflated catheter tip.

■ Coronary bypass is connection of a healthy section of vessel (usually the saphenous vein or internal thoracic artery) between the aorta and a coronary artery distal to an obstruction. Alternatively, the internal thoracic artery is connected to the coronary artery distal to the obstructive lesion. Bypass creates a new pathway for blood flow to the heart muscle.

■ Aortic aneurysm is a local dilation of the aorta that can lead to dissection or rupture. If located in the aortic arch, compression of the left recurrent laryngeal nerve may occur, leading to coughing, hoarseness, and paralysis of the ipsilateral vocal cord. Pressure on the esophagus may cause dysphagia (difficulty in swallowing), while dyspnea (difficulty in breathing) results from pressure on the trachea, root of the lung, or phrenic nerve.

■ Marfan syndrome is an inheritable disorder of connective tissue. It most often affects the heart and blood vessels (aortic root dilation, aortic aneurysm, aortic regurgitation, and mitral valve prolapse), the skeleton (long limbs), eye (dislocated lens), and lungs (spontaneous pneumothorax).

■ The coronary arteries arise from the ascending aorta. Systolic compression of the arterial branches in the myocardium reduces coronary blood flow. Therefore, maximal blood flow occurs during diastole.

■ The right coronary artery has the SA nodal, marginal, posterior IV, and AV nodal branches. The left coronary artery is shorter than the right one and divides into the anterior IV and circumflex arteries.

■ All cardiac veins, including the great, middle, small, and oblique cardiac veins, drain into the coronary sinus except the anterior cardiac vein, which drains into the right atrium.

■ Tetralogy of Fallot includes (1) pulmonary stenosis (narrowing of right ventricular outflow), (2) large overriding aorta (drains both ventricles), (3) VSD, and (4) right ventricular hypertrophy. It is characterized by right-to-left shunting of blood and cyanosis.

■ Overriding aorta (dextra-position of aorta) is that the aorta (its outlet) lies over both ventricles (instead of just the left ventricle), directly above the VSD, causing the aorta to arise from both ventricles.

■ Transposition of the great vessels occurs when the AP septum fails to develop in a spiral fashion, causing the aorta to arise from the right ventricle and the pulmonary trunk to arise from the left ventricle.

■ Patent ductus arteriosus results from failure of the ductus arteriosus to close after birth, and is common in premature infants. The ductus arteriosus takes origin from the left sixth aortic arch.

■ The fourth aortic arches contribute to the right subclavian artery on the right side and the aortic arch on the left.

■ The mediastinum is an interpleural space and consists of the superior mediastinum and inferior mediastinum. The inferior mediastinum further divides into the anterior, middle, and posterior mediastina.

■ The middle mediastinum contains the heart. The posterior mediastinum contains the esophagus, thoracic aorta, azygos and hemiazygos veins, thoracic duct, vagus nerves, and sympathetic splanchnic nerves.

■ Achalasia is a condition of impaired esophageal contractions resulting from degeneration of myenteric (Auerbach) plexus in the esophagus. The lower esophageal sphincter fails to relax during swallowing.

■ Systemic sclerosis (scleroderma) is a systemic collagen vascular disease and has clinical features of dysphagia for solids and liquids, severe heartburn, and esophageal stricture.

■ Coarctation of the aorta occurs when the aorta is abnormally constricted just inferior to the ductus arteriosus, in which case an adequate collateral circulation develops before birth. Clinical signs include hypertension and/or heart failure. It causes (a) a characteristic rib notching and a high risk of cerebral hemorrhage; (b) tortuous and enlarged blood vessels, especially the internal thoracic, intercostal, epigastric, and scapular arteries; (c) an elevated blood pressure in the radial artery and decreased pressure in the femoral artery; and (d) the femoral pulse to occur after the radial pulse (normally the femoral pulse occurs slightly before the radial pulse).

■ Stellate block is an injection of local anesthetic near the stellate ganglion by placing the tip of the needle near the neck of the first rib. It produces a temporary interruption of sympathetic function such as in a patient with excess vasoconstriction in the upper limb.

■ Injury to the recurrent laryngeal nerve may be caused by a bronchogenic or esophageal carcinoma, enlargement of mediastinal lymph nodes, an aneurysm of the aortic arch, or thyroid and parathyroid surgeries, causing respiratory obstruction, hoarseness, or an inability to speak because of paralysis of the vocal cord.

■ Vagotomy is transection of the vagus nerves at the lower portion of the esophagus in an attempt to reduce gastric secretion in the treatment of peptic ulcer.

■ The azygos vein is formed by the union of the right ascending lumbar and right subcostal veins. Its lower end is connected to the IVC. It arches over the root of the right lung and empties into the SVC.

■ The hemiazygos vein is formed by the union of the left subcostal and ascending lumbar vein, receives the 9th, 10th, and 11th posterior intercostal veins, and enters the azygos vein. Its lower end is connected to the left renal vein. The accessory hemiazygos vein receives the fifth to eighth posterior intercostal veins and terminates in the azygos vein.

■ The superior intercostal vein is formed by the second, third, and fourth intercostal veins and drains into the azygos vein on the right and the brachiocephalic vein on the left.

■ The thoracic duct begins in the abdomen at the cisterna chyli, which is the dilated junction of the intestinal, lumbar, and descending intercostal trunks. It drains all parts of the body except the right head, neck, upper limb, and thorax, which are drained by the right lymphatic duct. It passes through the aortic opening of the diaphragm, ascends between the aorta and the azygos vein, and empties into the junction of the left internal jugular and subclavian veins.

■ The greater splanchnic nerve arises from the fifth through ninth thoracic sympathetic ganglia and ends in the celiac ganglion. The lesser splanchnic nerve arises from the 10th and 11th thoracic sympathetic ganglia and ends in the aorticorenal ganglion. The least splanchnic nerve arises from the 12th thoracic sympathetic ganglia and ends in the renal plexus. All of these splanchnic nerves contain preganglionic sympathetic GVE fibers with cell bodies located in the lateral horn (intermediolateral cell column) of the spinal cord and GVA fibers with cell bodies located in the dorsal root ganglia.

·        White rami communicantes contain preganglionic sympathetic GVE fibers with cell bodies located in the lateral horn of the spinal cord and GVA fibers with cell bodies located in the dorsal root ganglia. They are connected to the spinal nerves and limited to spinal cord segments between T1 and L2.

■ Gray rami communicantes contain postganglionic sympathetic GVE fibers with cell bodies located in the sympathetic chain ganglia. They are connected to every spinal nerve and supply the blood vessels, sweat glands, and arrector pili muscles of hair follicles.

Reference: 

1. BRS Gross anatomy.

2. Gross Anatomy: The Big Picture. 

3. High Yield Gross Anatomy.

4. Clinical Anatomy by Regions, Snell. 

5. Grays Anatomy .

6. LAST Anatomy