Thoracic Anatomy, Mediastinum, Lungs, Pleura, and Intercostal Structures

Comprehensive practice flashcards covering thoracic anatomy, mediastinal divisions and layers, bony thorax, intercostal muscles and neurovascular bundle, pleura, lungs, bronchopulmonary segments, and intercostal vessels.

What is the mediastinum?

The central compartment of the thoracic cavity containing a group of structures within the thorax, located between the right and left pleural cavities.

How is the mediastinum primary subdivided?

It is divided into the superior mediastinum and inferior mediastinum, with the inferior mediastinum further subdivided into anterior, middle, and posterior parts.

What structure is located in the retromanubrial layer of the superior mediastinum?

Remnant of the thymus gland (or thymic fat in adults).

Which structures form the venous layer of the superior mediastinum?

Right and left brachiocephalic veins, upper part of the superior vena cava (SVC), and the right phrenic nerve.

What structures are contained in the arterial layer of the superior mediastinum?

Arch of the aorta and its branches, bifurcation of the pulmonary trunk, ligamentum arteriosum, left vagus nerve, left phrenic nerve, and left recurrent laryngeal nerve.

Which structures comprise the tubal layer of the superior mediastinum?

Trachea, esophagus, right vagus nerve, thoracic duct, and tracheobronchial lymph nodes.

What structures lie in the prevertebral layer of the superior mediastinum?

Sympathetic trunk (sympathetic chain), azygos vein, and longus colli muscle.

What are the anatomical contents of the anterior mediastinum?

Remains of the thymus, superior and inferior sternopericardial ligaments, and mediastinal branches of the internal thoracic artery.

What structures are present within the middle mediastinum?

Pericardium, heart, ascending aorta, pulmonary trunk, terminal parts of right and left pulmonary veins, lower half of superior vena cava, and terminal part of inferior vena cava.

What are the key contents of the posterior mediastinum?

Descending thoracic aorta, esophagus, thoracic duct, right and left vagi, right and left sympathetic chains, azygos vein, superior hemiazygos vein, and inferior hemiazygos vein.

What structures form the boundaries of the thoracic inlet?

Upper border of the manubrium sterni anteriorly, body of the 1st thoracic vertebra posteriorly, and the inner border of the 1st rib on each side laterally.

What are the attachments of the suprapleural membrane (Sibson's Fascia)?

The apex attaches to the transverse process of the C7 vertebra, and the base attaches to the inner border of the 1st rib and its costal cartilage.

What are the three main functions of the suprapleural membrane?

It protects the cervical pleura and apex of the lung, prevents inward suction of structures at the root of the neck during inspiration, and prevents upward bulging of the apex of the lung during forcible expulsive expiration.

What clinical manifestations can result from pressure exerted by a cervical rib?

Pressure on the lower trunk of the brachial plexus causes sensory troubles along the medial side of the forearm and wasting of small hand muscles; pressure on the subclavian artery causes ischemic manifestations of the upper limb.

At what vertebral level does the sternal angle (of Louis) lie, and what is its clinical significance?

It lies at the level of the intervertebral disc between T4 and T5, forming a palpable transverse ridge anteriorly that demarcates the 2nd costal cartilages.

Why is the sternum a suitable site for bone marrow puncture?

Because it contains red marrow throughout life, is subcutaneous, and possesses a thin layer of cortical bone.

How are ribs classified based on sternal attachment?

True ribs (vertebrosternal, ribs 1–7), false ribs (vertebrochondral, ribs 8–10), and floating ribs (vertebral, ribs 11–12).

Which ribs are considered typical and which are non-typical (atypical)?

Ribs 3 to 9 are typical ribs; ribs 1, 2, 10, 11, and 12 are non-typical (atypical) ribs.

What structures run within the costal groove of a typical rib?

The intercostal vein, artery, and nerve (VAN), arranged from above downwards.

Where do ribs usually break in crushing injuries, and which ribs are least commonly fractured?

Ribs usually break at their angles (their weakest point). The upper two ribs (protected by the clavicle) and lower two ribs (free floating) are the least commonly fractured.

What causes paradoxical movements of respiration in severe thoracic crush injuries?

Fracture of several ribs at two sites creates a loose flap of the thoracic cage that is sucked in during inspiration and blown out during expiration.

Which thoracic vertebrae are classified as typical versus non-typical?

Thoracic vertebrae T2 to T8 are typical thoracic vertebrae; T1, T9, T10, T11, and T12 possess unique features and are non-typical.

What are the three layers of intercostal muscles from outer to inner?

Outer layer: external intercostal; Middle layer: internal intercostal; Inner layer: innermost intercostal.

What is the direction of fibers and extent of the external intercostal muscle?

Fibers run obliquely downwards and forwards. It extends from the tubercle of the rib posteriorly to the costochondral junction anteriorly, where it continues as the anterior intercostal membrane to the sternum.

What is the direction of fibers and extent of the internal intercostal muscle?

Fibers run obliquely downwards and backwards. It extends from the sternum anteriorly to the angle of the rib posteriorly, where it continues as the posterior intercostal membrane.

What is the spatial extent of the innermost intercostal muscle?

It extends from the midaxillary line (MAL) anteriorly to the angle of the rib posteriorly, occupying the middle 2/4 of the space.

What are the functional actions of the intercostal muscles?

External intercostals elevate the ribs (inspiratory muscles); internal and innermost intercostals depress the ribs (expiratory muscles). They also prevent intercostal spaces from being sucked in during inspiration or puffed out during expiration.

Which intercostal nerves are considered typical intercostal nerves?

The 3rd to 6th intercostal nerves (anterior primary rami of T3 to T6), which run their entire course within the thoracic wall.

Where does a typical intercostal nerve run relative to the intercostal muscles in the costal groove?

It runs in the neurovascular plane between the internal intercostal muscle and innermost intercostal muscle, lying below the intercostal vessels.

What is the intercostobrachial nerve and what area does it supply?

It is the lateral cutaneous branch of the 2nd intercostal nerve; it crosses the axilla to supply skin over the floor of the axilla and the upper half of the medial side of the arm.

What viral condition causes severe burning sensation and vesicles along an intercostal nerve course?

Herpes zoster virus infection.

What are the four anatomical subdivisions of the parietal pleura?

Cervical pleura, costal pleura, mediastinal pleura, and diaphragmatic pleura.

What is the location and function of the pulmonary ligament?

A double-layer fold of mediastinal pleura spanning between the esophagus medially and lung laterally; it provides a dead space allowing distention of pulmonary veins during increased venous return and free movement of the lung root.

What are the two main pleural recesses, and when do the lungs enter them?

The costomediastinal recess and costodiaphragmatic recess; they receive the expanding anterior and inferior borders of the lung, respectively, only during forced inspiration.

How does nerve supply and pain sensitivity differ between visceral and parietal pleura?

Visceral pleura receives autonomic innervation (pulmonary plexuses) and is insensitive to pain and temperature; parietal pleura receives somatic innervation (intercostal and phrenic nerves) and is highly sensitive to pain.

Why does irritation of the mediastinal or central diaphragmatic pleura cause referred pain to the shoulder tip?

Because they are innervated by the phrenic nerve ($C3, C4, C5$), which shares spinal segments with the supraclavicular nerves ($C3, C4$) supplying the shoulder tip.

What is the correct location and technique for pleural fluid aspiration (thoracocentesis)?

A large needle is introduced in the 7th intercostal space along the midaxillary line, midway between the upper and lower boundaries of the space to avoid injuring neurovascular bundles.

What structures form the hilum of the right lung from anterior to posterior and superior to inferior?

Superior lobar (eparterial) bronchus (above), principal bronchus (posterior), pulmonary artery (between principal bronchus and superior vein), superior pulmonary vein (most anterior), and inferior pulmonary vein (most inferior).

What structures compose the hilum of the left lung?

Principal bronchus (most posterior), superior pulmonary vein (most anterior), inferior pulmonary vein (most inferior), and pulmonary artery (above and in front of principal bronchus).

What fissure is unique to the right lung, and what lobes does it separate?

The horizontal fissure; it separates the upper lobe from the middle lobe of the right lung.

What distinct features are present on the anterior border of the left lung?

The cardiac notch and the lingula.

What impressions and grooves exist on the mediastinal surface of the right lung?

Cardiac impression (right atrium, auricle, right ventricle), SVC groove, IVC groove, arch of azygos vein groove, tracheal groove, and esophageal groove.

What impressions and grooves exist on the mediastinal surface of the left lung?

Cardiac impression (left ventricle, left atrium, RV, pulmonary trunk), arch of aorta groove, left common carotid artery groove, left subclavian artery groove, esophageal groove, and descending thoracic aorta groove.

What defines a bronchopulmonary segment?

A functionally independent unit of lung tissue supplied by a segmental bronchus and a branch of the pulmonary artery, having its own lymphatics and innervation, separated by intersegmental connective tissue septa containing pulmonary veins.

How many bronchopulmonary segments are in the right lung versus the left lung?

The right lung has 10 segments (3 upper, 2 middle, 5 lower); the left lung has 8 segments (4 upper, 4 lower).

Why does the left lung contain 8 bronchopulmonary segments instead of 10?

Because the 1st (apical) and 2nd (posterior) segmental bronchi arise by a common stem (apicoposterior), and the 7th (medial basal) segmental bronchus is frequently absent.

What is the origin of the anterior intercostal arteries across the intercostal spaces?

In the upper 6 intercostal spaces, they arise from the internal thoracic artery; in the 7th, 8th, and 9th spaces, they arise from the musculophrenic artery.

What is the origin, course, and termination of the internal thoracic artery?

It originates from the 1st part of the subclavian artery, descends vertically $1\,\text{cm}$ lateral to the sternum behind the upper 6 costal cartilages, and terminates in the 6th intercostal space by dividing into the musculophrenic and superior epigastric arteries.

What is the origin of the posterior intercostal arteries for spaces 1–2 versus spaces 3–11?

For the 1st and 2nd spaces: superior intercostal artery (from costocervical trunk of 2nd part of subclavian artery); for the 3rd to 11th spaces: descending thoracic aorta.

Why do the 10th and 11th posterior intercostal arteries terminate in the abdominal wall muscles?

Because of the absence of 10th and 11th anterior intercostal arteries.

How do the anterior intercostal veins drain on each side of the thoracic wall?

Veins of spaces 7–9 drain into musculophrenic veins; spaces 4–6 drain into internal thoracic venae comitantes (forming internal thoracic vein at 3rd costal cartilage); upper 3 spaces drain directly into the internal thoracic vein.

How do the posterior intercostal veins drain on the right side of the thorax?

1st vein drains into right brachiocephalic vein; 2nd and 3rd unite to form right superior intercostal vein (drains into arch of azygos); 4th to 11th drain directly into the azygos vein.

How do the posterior intercostal veins drain on the left side of the thorax?

1st vein drains into left brachiocephalic vein; 2nd and 3rd form left superior intercostal vein (drains into left brachiocephalic vein); 4th to 8th drain into accessory (superior) hemiazygos vein; 9th to 11th drain into hemiazygos (inferior hemiazygos) vein.