Anatomy Module 6

Thoracic Wall

• Thorax: The part of the body between the neck and abdomen. It's also broader, including the shoulders and breasts.
• Thoracic Cavity: Shaped like a truncated cone, containing the pleural and pericardial cavities, and the mediastinum.
• Functions: Protects vital organs, resists pressure changes during breathing, provides attachment for upper limbs, and anchors muscles for trunk position.
• Structure: Made of the thoracic cage (rib cage), ribs, costal cartilages, sternum, and thoracic vertebrae. The floor is the diaphragm.

Types of Ribs

• True Ribs (1-7): Directly attach to the sternum via their costal cartilages.
• False Ribs (8-10): Connect to the sternum indirectly, attaching to the cartilage of the rib above.
• Floating Ribs (11-12): Have rudimentary cartilages and do not connect to the sternum, ending in posterior abdominal musculature.

Typical Ribs (e.g., 3-9)

• Components:
  • Head: Forms a joint with the bodies of two thoracic vertebrae.
  • Neck: Connects the head to the tubercle.
  • Tubercle: Located at the junction of the neck and body, articulates with the corresponding transverse process of vertebrae.
  • Body (Shaft): Thin, flat, and curved with a costal groove, protecting intercostal nerves and vessels.

Atypical Ribs (1, 2, 10-12)

• Variations: Differences in shape, number of facets, grooves, or the absence of a neck or tubercle. Examples include the wider, nearly horizontal, and shortest rib, the first ribs with a single facet on the head, and the presence of grooves for subclavian vessels and absence of a neck or tubercle.

Thoracic Vertebrae

• Features: Long, inferiorly slanting spinous processes, bilateral costal facets (demifacets) on vertebral bodies, costal facets on transverse processes (for articulation with tubercles of ribs).

Sternum

• Structure: Flat, elongated bone forming the middle of the anterior part of the thoracic cage. Composed of three parts: manubrium, body, and xiphoid process.
• Features: Jugular (suprasternal) notch, clavicular notches, and sternal angle.

Thoracic Apertures

• Superior Aperture: Bounded posteriorly by vertebra T1, laterally by the first pair of ribs, and anteriorly by the superior border of the manubrium.
• Inferior Aperture: Bounded posteriorly by vertebra T12, posterolaterally by the 11th and 12th pairs of ribs. Costal cartilage, and anteriorly formed by by the xiphisternal joint.

Joints of the Thoracic Wall

• Intervertebral: Between vertebrae T1-T12.
• Costovertebral: Joints of head of rib.
• Costotransverse: Connects ribs and transverse processes.
• Costochondral: Articulates with costal cartilage.
• Sternocostal: Connects costal cartilage and sternal end of rib.
• Sternoclavicular: The sternal end of the clavicle articulates with the manubrium of the sternum.
• Manubriosternal: Articulation between the manubrium and the body of the sternum.
• Xiphisternal: Connects the body of the sternum to the xiphoid process.

Muscles of the Thoracic Wall & Innervation

- Includes muscles such as serratus posterior superior and inferior, levator costarum, external and internal intercostals.
-Subcostal (internal thoracic muscles) & Transversus thoracis
- Main functions for inspiration/expiration and proprioception

Nerves of Thoracic Wall

• Costal nerves: sensory and motor branches supplying the region.
• Intercostal nerves: run in intercostal grooves, innervating muscles.

Arteries of the Thoracic Wall

• Posterior intercostal arteries which originate in the thoracic aorta, superior intercostal artery, internal thoracic artery & musculophrenic arteries,
• Subcostal arteries branch off from the thoracic aorta.
• Collateral branches from anterior and posterior intercostal arteries.

Veins of the Thoracic Wall

• Posterior intercostal veins anastomose (join) with anterior intercostal veins, which are tributaries of internal thoracic veins. The intercostal veins accompany the arteries and nerves, lying in the superior part of the costal grooves. Most posterior intercostal veins (4-11) drain into the azygos/hemi-azygos system, which channels blood into the superior vena cava.

Lungs and Pleura

• Compartments: Pulmonary cavities (each side) and Central Mediastinum
• Pleura: Visceral (lung surface), Parietal (thoracic wall). Pleural cavity.
• Extensions and reflections of the pleura. Costal, mediastinal, diaphragmatic pleura. Regions where pleura shifts from one region to another and Costodiophragmatic recesses.
• The parietal pleura covers the internal surfaces of the thoracic wall, mediastinal surfaces/roots of the lungs.

Tracheobronchial Tree

• Trachea: Divides into two main bronchi (right and left).
• Bronchi: Main bronchi branch into lobar (secondary) bronchi, then segmental (tertiary) bronchi that divide into bronchioles.

Bronchopulmonary Segments

• Subdivisions of a lobe in the lung, each supplied independently by a segmental bronchiole, and pulmonary artery branch.

Bronchi in Conducting Zone

• Primary bronchi are the largest.
• Secondary (lobar) & tertiary (segmental) bronchi progressively lessen in diameter toward the bronchioles.
• Bronchioles are progressively smaller and progressively less in structural support.

Lungs

• Apex and Base: Blunt superior and concave inferior surfaces.
• Fissures: Divide each lung into lobes.
• Three surfaces (costal, mediastinal, diaphragmatic) and 3 borders of each lung.
• Right lung (3 lobes): Superior, middle, inferior. Left lung (2 lobes): Superior & inferior.

Arterial Supply to the Lungs

- Bronchial arteries supply blood for nutrition in the walls of all of the conducting passageways and supporting lung tissue and visceral pleura.

• Common Origin: Two left bronchial arteries arise directly from the thoracic aorta and a common trunk of left superior bronchial artery and many arise indirectly from posterior intercostal arteries. Single right bronchial artery commonly arises from the posterior intercostal arteries or from a common trunk with left superior bronchial artery.

Veins of the Lungs

- Pulmonary veins carry oxygenated blood back to the heart, arising from within the pulmonary tissue and uniting to form the

bronchial veins, which drain into the azygos and/or hemiazygos veins.

Pulmonary Lymphatic Plexuses

• Superficial (subpleural) drains into bronchopulmonary lymph nodes.
• Deep drains into Intrinisc Pulmonary lymph nodes; all ultimately drain to superior and inferior tracheobronchial lymph nodes & subsequently into bronchomediastinal trunks.

Nerves of the Lungs and Pleura

• Parasympathetic: Primarily vagal nerves causing bronchoconstriction, vasodilation, and secretomotor.
• Sympathetic: Cause bronchodilation, vasoconstriction,
• Visceral afferent: Sensory fibers that relay reflex and pain impulses

Clinical Correlates (brief)

• Pneumothorax: Air in the pleural space causing lung collapse, often due to a leak or trauma.
• Hemothorax: Blood in the pleural space, commonly due to trauma.