Anatomy of the Thorax

Study Notes

The thorax is the chest cavity, enclosed by the ribs, sternum, and vertebral column.
The thorax contains three major compartments:
- Left pleural cavity
- Right pleural cavity
- Mediastinum
The pleural cavities contain the lungs, while the mediastinum contains the heart, great vessels, trachea, esophagus, and thymus.
The pleura is a thin, serous membrane that surrounds the lungs.
- The visceral pleura covers the lungs.
- The parietal pleura lines the thoracic cavity wall.
- The space between the visceral and parietal pleura is called the pleural space.
- The costodiaphragmatic recess is the space inferior to the lungs that expands during inspiration, allowing more lung volume.
The sternal angle is an important landmark in the thorax because it marks the level of:
- The superior portion of the pericardium
- The beginning and end of the aortic arch
- The entrance of the superior vena cava into the heart
- The bifurcation of the trachea
- The superior limit of the pulmonary trunk
The phrenic nerves supply the diaphragm, originating from C3, C4, and C5, and control its contractions.

The lungs are the primary organs of respiration, located within the pleural cavities.
The right lung has three lobes: the superior, middle, and inferior lobes, separated by the oblique and horizontal fissures.
The left lung has two lobes: the superior and inferior lobes, separated by the oblique fissure.
The pulmonary arteries carry deoxygenated blood from the heart to the lungs.
- The pulmonary veins carry oxygenated blood from the lungs back to the heart.
The lungs are supplied by the bronchial arteries, which bring oxygenated blood to the lung tissues.
The airways of the lungs consist of the trachea, bronchi, bronchioles, and alveoli.
- The trachea branches into the right and left main stem bronchi.
- The bronchi further divide into lobar bronchi, segmental bronchi, and bronchioles.
The lungs are innervated by the vagus nerve (parasympathetic) and the sympathetic trunk, which control bronchodilation and bronchoconstriction.

The mediastinum is the central compartment of the thorax, containing the heart and great vessels.
The middle mediastinum specifically contains the heart.

The heart is a muscular organ responsible for pumping blood throughout the body.
The pericardium is a double-layered sac that surrounds the heart.
- The fibrous pericardium is the outer layer.
- The serous pericardium is the inner layer, consisting of a parietal layer and a visceral layer.
- The space between the parietal and visceral layers is called the pericardial space.
Surface features of the heart include the sulci, which are grooves that mark the boundaries of the heart chambers.
- Coronary arteries and veins run through the sulci, supplying the heart with oxygenated blood and removing deoxygenated blood.
Internally, the heart is divided into four chambers:
- The right atrium and ventricle receive deoxygenated blood.
- The left atrium and ventricle receive oxygenated blood.
The right atrium receives blood from the superior and inferior vena cava and the coronary sinus.
The right ventricle pumps deoxygenated blood to the lungs through the pulmonary valve.
The left ventricle pumps oxygenated blood to the body through the aortic valve.
Valves within the heart prevent backflow of blood.
- The tricuspid valve regulates blood flow between the right atrium and right ventricle.
- The mitral valve regulates blood flow between the left atrium and left ventricle.
- The pulmonary valve regulates blood flow between the right ventricle and pulmonary trunk.
- The aortic valve regulates blood flow between the left ventricle and aorta.