8th November 2012
The lungs extend from the diaphragm to just slightly superior to the clavicles and lie against the ribs anteriorly and posteriorly. The base of the lung is concave and fits over the convex area of the diaphragm. The narrow superior portion of the lung is called the apex. The apices of the lungs extend about three centimetres above the medial third of the clavicles. The medial surface of the lung is called the hilum. The hilus of the lungs is through which the bronchi, pulmonary blood vessels and nerves enter and exit. Anteriorly, they lie at the level of the costal cartilages 3-4, which is at the level of T5-7. The inferior margins of the lungs are: T-6 mid-clavicular line, T-8 at the mid-axilla, and T-10 posteriorly. Each lung is contained and protected within a double-layered membrane called the pleural membrane. The superficial layer, known as the parietal pleura affects the anterior margins of the lungs on either side. On the right, it is deep to the right side of the sternum between the second and fourth costal cartilages inferiolaterally to the level of the deep surface of the sixth right intercostal cartilage. On the left, deep to the sternum near the midline, inferiorly between the levels of costal cartilages 2 and 4, displaced laterally and more obliquely than left side to a point about 3 centimetres lateral to the left sternal edge at the upper margin of the sixth costal cartilage. The space created by the lateral deviation of pleura and lung on the left side is termed the cardiac notch.
The heart rests on the diaphragm, near the midline of the thoracic cavity in the mediastinum. An important and readily palpable landmark for the heart is the sternal angle. The sternal angle is the junction between the manubrium and the body of the sternum, and corresponds to the second costal cartilage. The apex of the heart, which is formed by the tip of the left ventricle, rests on the...