Thorax Anatomy Basics

Study Notes

The thorax is an irregularly shaped cylinder with a superior thoracic aperture and inferior thoracic aperture.
The superior aperture is open, connecting to the neck; the inferior is closed by the diaphragm.
The thoracic wall is flexible, composed of segmentally arranged vertebrae, ribs, muscles, and the sternum.
The thoracic cavity is divided into three main compartments: right pleural cavity, left pleural cavity, and mediastinum.
The mediastinum is a flexible partition containing the heart, esophagus, trachea, major nerves, and systemic blood vessels.
Pleural cavities are completely separated by the mediastinum, preventing abnormal events in one from affecting the other.
The apex of each lung extends into the neck, making the pleura and lung susceptible to neck issues.

Breathing: The thorax facilitates breathing through the diaphragm and movements of the ribcage that alter thoracic cavity volume.
Protection: Houses and safeguards vital organs such as the heart and lungs.
Serves as a conduit: Supports the passage of structures between the thorax and abdomen.

Rib I's joint with the manubrium is fibrocartilaginous; ribs II to VII have synovial joints with reinforced capsules.
Interchondral joints occur between adjacent costal cartilages and provide indirect anchorage to the sternum.
Manubriosternal and xiphisternal joints are usually symphyses, allowing slight angular movements.
The sternal angle, palpable at the manubriosternal joint, marks the articulation of rib II and separates the superior from the inferior mediastinum.

Posterior intercostal arteries branch from the aorta and supply the thoracic wall; anterior intercostal arteries arise from the internal thoracic artery.
The internal thoracic artery branches into the superior epigastric and musculophrenic arteries at the sixth intercostal space.
Anterior intercostal arteries have branches that usually create anastomotic connections with posterior intercostal arteries.

Venous drainage parallels arterial supply, channeling blood through axillary and internal thoracic veins.

The diaphragm is the primary separator of the thorax from the abdomen.
It allows passage for the inferior vena cava (at TVIII), esophagus (at TX), and aorta (at TXII).

The pectoral region consists of superficial (skin, fascia, and breasts) and deep compartments (muscles).
Structures in the superficial compartment emerge from the thoracic wall, axilla, and neck.

Breasts comprise mammary glands, associated skin, and connective tissues, acting as modified sweat glands.
Mammary glands have ducts converging into 15-20 lactiferous ducts that open at the nipple, surrounded by the areola.
A well-developed stroma supports the ducts and lobules; tension on suspensory ligaments may indicate carcinoma.
Nonlactating breasts are primarily fatty tissue, while glandular tissue increases during lactation.

Vascular supply includes arteries from the axillary artery, internal thoracic artery, and intercostal arteries.
Venous drainage mirrors arterial supply, leading to axillary, internal thoracic, and intercostal veins.

Innervation comes from cutaneous branches of the second to sixth intercostal nerves; the nipple is specifically innervated by the fourth intercostal nerve.
Lymphatic drainage primarily targets axillary nodes (75%) and parasternal nodes, with additional drainage via intercostal lymphatics.

Male breasts are rudimentary with small ducts, lacking significant extension beyond the areola; breast cancer is a risk for men too.

Contains significant muscles: pectoralis major, pectoralis minor, and subclavius, all originating from the thoracic wall and inserting in upper limb bones.