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1. Describe the pleura, including the recesses/potential spaces created by the pleural sacs, and the margins of these recesses at the midclavicular, midaxillary, and paravertebral lines.   Understand how this anatomy relates to clinical conditions and procedures.

The pulmonary cavities contain the pleurae. The outer margins of the pulmonary cavities are lined with parietal pleurae, whereas visceral pleurae adhere to all surfaces of the lungs. 

The parietal pleurae each have 3-4 parts:

• Costal pleura, which covers the ribs and intercostal spaces

  • innervated be intercostal nn.

• Diaphragmatic pleura, which covers the superior surface of the diaphragm

  • innervated by intercostal nn. peripherally and phrenic nn. centrally

• Mediastinal pleura. which covers the mediastinal borders of the pulmonary cavities

  • innervated by phrenic nn.

• Cervical pleura (extensions of the mediastinal and costal parts) which forms domes over the apices of each lung.

The visceral afferent fibers from the visceral pleura accompany sympathetic fibers.

The spaces between parietal and visceral pleurae are the pleural cavities.

There are two important recesses associated with the pleural cavities. Both are potential spaces between reflections of different parts of parietal pleurae.

Costodiaphragmatic recesses: potential spaces between the diaphragmatic and costal parietal pleurae. The lungs (covered by visceral pleura) sit above these recesses, and may enter into them during inspiration.

• • The margins of this recess vary based on anatomical line:

    • Between 6th - 8th ribs at the midclavicular line

    • Between 8th - 10th ribs at the midaxillary line

    • Between 10th - 12th ribs at the paravertebral line

Costodiaphragmatic recesses offer access to the pleural cavities without jeopardizing the integrity of the lung tissues. For instance, understanding the boundaries of these recesses offers a clinician a target for thoracentesis (pleural tap). 

Costomediastinal recesses: potential spaces between the costal and mediastinal parietal pleurae

• • The left costomediastinal recess is larger because of the location of the heart and the cardiac notch of the left lung.

2. Describe the right and left lung’s surface anatomy, including fissures, lobes, apex, base, hilum. Differentiate between the left and right lungs. 

Structures common to both lungs:

• • Apex: superior portion, which extends into the root of the neck and covered with both visceral pleura and cervical parietal pleura

  • Base: inferior portion, closely associated with diaphragm

  • Borders: three borders (anterior, inferior, and posterior)

  • Fissures: both lungs have an oblique fissure, which separates superior & inferior lobes

  • Lobes: both lungs have a superior & inferior lobe

  • Surfaces: three surfaces (costal, diaphragmatic, and mediastinal)

    • • Costal surface: largest and convex

        • Related to costal parietal pleura, which is associated with ribs and costal cartilages, bodies of thoracic vertebrae, and innermost intercostal mm.

      • Diaphragmatic surface: most inferior surface, concave

        • Related to diaphragm and base of lung

      • Mediastinal surface: medial and concave surface

        • Related to middle mediastinum

Structures specific to right lung:

• • The overall structure of the right lung is heavier and shorter than the left lung due to the close relationship of the more superior extension of the right hemidiaphragm. There are two fissures (oblique and horizontal) and three lobes (superior, middle, and inferior).

Structures specific to left lung:

• • The anterior border of the left lung has a deep indentation, the cardiac notch, caused by close association of the apex of the heart. Inferior to the cardiac notch is a small extension of the superior lobe, the lingula.

3. Diagram the airway path – i.e., tracheobronchial tree – from trachea to segmental bronchi.  Identify cartilages associated with creating an emergency airway. 

Any of the airway path inferior to the larynx is considered a component of the tracheobronchial tree. The larynx transitions into the trachea (trunk of tracheobronchial tree) at the inferior border of the cricoid cartilage (approximately C6-level). The bifurcation of the trachea into a right and left main bronchus occurs at the level of the sternal angle. There are important differences between the R. and L. main bronchi, including:

• • Right main bronchus: more vertical in orientation, wider, and shorter

    • Aspirated materials are more likely to enter into the R. main bronchus (and certain branches) due to its orientation.

  • Left main bronchus: more horizontal in orientation and longer

The R. and L. main bronchi enter the hila of the lungs. Further branching occurs within the parenchyma of the lungs.

The first set of branching within the lungs is into secondary (lobar) bronchi, which are associated with the lobes of the lungs. Therefore, there are 3 right, secondary (lobar) bronchi and 2 left, secondary (lobar) bronchi.

Secondary (lobar) bronchi further branch into tertiary (segmental) bronchi, which will serve the bronchopulmonary segments. There are 10 tertiary (segmental) bronchi associated with the right lung, and typically 8 (and sometimes up to 10) tertiary (segmental) bronchi for the left lung. If an individual is supine and the aspirated material is small enough, it is more likely to lodge in the superior segmental bronchus of the R. inferior lobe, due to the posterior direction of this segment.

The rest of the tracheobronchial tree branching occurs at a level that is difficult/impossible to see at a gross level.

Tertiary (segmental) bronchi → conducting bronchioles → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveolar sacs

Emergency Airways

• • Tracheostomy: incision through the anterior neck and trachea typically between the 1st and 2nd tracheal rings and occasionally more inferior. A tracheostomy tube is entered through the incision to establish an airway

• • Cricothyrotomy: for a more emergent situation, an incision is made through the anterior neck and median cricothyroid ligament (between the thyroid and cricoid cartilages) for immediate entry of air.

4. Understand the difference between pulmonary and bronchial vasculature.

Pulmonary arteries are of pulmonary circulation, and carry relatively de-oxygenated blood to the lungs for oxygenation. The typical pattern of branching is as follows:

• • Pulmonary trunk bifurcates near the level of the sternal angle → R. & L. pulmonary aa. (part of root of lung; enters hilum of lung) → secondary lobar aa. (branch for each lobe of the lung) → tertiary segmental aa. (branch for each bronchopulmonary segment)

  • The pulmonary aa. branches travel in close association with the various branches of the tracheobronchial tree.

Pulmonary veins carry relatively oxygenated blood to the L. atrium of the heart, destined for systemic circulation. For both lungs there are a superior and inferior pulmonary vein, and additionally, the R. lung has a middle lobe vein, which is typically a tributary of the superior pulmonary vein. It is important to note that the tributaries of the pulmonary veins course independent of the paired pulmonary aa. and tracheobronchial tree branches.

Bronchial arteries are of systemic circulation, and supply oxygenated blood to bronchi, visceral pleurae, hila of the lungs, bronchopulmonary (hilar) lymph nodes, a portion of the esophagus, and other connective tissues. There are two left bronchial arteries, and these arteries typically branch directly from the thoracic aorta. There is typically only one right bronchial artery, and it is variable in its branching pattern. The most common branching pattern is from the right 3rd posterior intercostal a., but it can also branch from the L. superior bronchial artery or directly from the thoracic aorta.

Bronchial veins typically play a supporting role in drainage of lung tissues and associated tissues to the pulmonary veins, usually only draining tissues around the roots of the lungs. The L. bronchial drains into either the accessory hemi-azygos v. or the left superior intercostal v. The R. bronchial v. typically drain directly into the azygos v.

5. Describe the basic structure of the diaphragm, and identify its neurovascular supply.

The diaphragm is the muscular division between the thoracic and abdominopelvic cavities. The muscular fibers of the diaphragm originate circumferentially from the thoracic outlet/inferior thoracic aperture (an uneven ring following the inferior margins of the 11th and 12th ribs, the costal cartilages, and the xiphisternal junction), and insert on the central tendon.

There are 3 major apertures of the diaphragm:

• • Caval opening (at T8)

    • Contents: inferior vena cava, right phrenic n., & lymphatics

  • Esophageal hiatus (at T10)

    • Contents: esophagus, anterior & posterior vagal trunks, esophageal branch of left gastric a., & lymphatics

  • Aortic hiatus (at T12)

    • Contents: descending aorta, thoracic duct, & branch of the azygos v.

There are 2 smaller, bilateral hiatuses within the crura that transmit the greater and lesser splanchnic nerves.

Innervation: The phrenic nn. provide efferent innervation to the diaphragm ("C3, 4, & 5 keep the diaphragm alive"), while afferent innervation is distributed by the phenic nn. and the 6th-7th intercostal nn.

Vascular supply: The dominant blood supply to the diaphragm is from the inferior phrenic aa., but also receives supply from the superior phrenic aa., inferior 5 intercostal aa., and the subcostal aa.

6. Describe the basic structure of the autonomic innervation of the thoracic viscera with a special emphasis on the pulmonary plexuses. 

Thoracic viscera are affected by sympathetic and parasympathetic innervation. In general, all thoracic viscera derive sympathetic innervation from T1-T5/6 spinal cord levels, while parasympathetic innervation is derived from the vagus n. (CN X).

There are three main autonomic plexuses associated with thoracic viscera: cardiac, pulmonary, and esophageal. All plexuses are continuous.

Cardiac plexus: there are two parts of the cardiac plexus: superficial (located inferior to arch of aorta and sandwiched between arch and pulmonary trunk) & deep (located between arch of aorta and tracheal bifurcation).

• • Sympathetic function: dilate coronary arteries and accelerates heart rate

  • Parasympathetic function: constrict coronary arteries and slows heart rate

Pulmonary plexus: located anterior and posterior to the root of the lungs; continuous with cardiac plexus (easily observable at tracheal bifurcation) and esophageal plexus

• • Sympathetic function: bronchodilation and constriction of pulmonary vasculature

  • Parasympathetic function: maintenance of tone or bronchoconstriction of smooth muscle of bronchi, increased mucus production, and dilation of pulmonary vasculature

Esophageal plexus: surrounding the inferior 2/3rds of the esophagus (inferior to root of lungs)

• • Sympathetic function: vasoconstriction of esophageal vasculature

  • Parasympathetic function: peristalsis of smooth muscle

  • The superior 1/3rd of the esophagus is composed of skeletal muscle and is innervated by the recurrent laryngeal n. and sympathetic fibers