The organs of the thorax include the thymus gland, breasts, heart, lungs, tracheobronchial tree, and pleurae. The thymus gland is found in the superior mediastinum of the thoracic cavity but may extend downward into the neck. Classified as a lymphoid organ, it plays an important part in the development of the immune system. After puberty, the thymus gland begins involution, where it shrinks in size and is eventually replaced with fat.
The pair of breasts are found in the pectoral region of both males and females. Females, however, possess mammary glands that are used to provide nourishment for their offspring. It is essential to understand the lymphatic drainage in breast tissue as cancer cells can use it as a means to metastasize.
The heart, located in the middle mediastinum of the thoracic cavity, is surrounded by some large vessels. It comprises four chambers and a wall that is made up of three different layers. The right side of the heart pumps blood into the pulmonary circulation while the left pumps blood into the systemic circulation. The four valves of the heart ensure the blood flows through it in a single direction. For extra protection, the heart is surrounded by a fluid-filled sack called the pericardium. It has its own independent arterial and venous drainage systems.
The tracheobronchial tree, made up of the trachea, bronchi, and bronchioles, allows air to enter the lungs. The lungs are the main respiratory organs as they bring deoxygenated blood from the heart and inspired air into close contact, enabling gas exchange to take place. Covering the lungs and thoracic cavity are the pleurae, two-part serous membranes that guarantee effective respiration.
