Final answer:
The cardiac notch is an indentation on the medial surface of the inferior lobe of the left lung that accommodates the apex of the heart, making the left lung smaller than the right lung.
Step-by-step explanation:
The cardiac notch is an indentation on the medial surface of the inferior lobe of the left lung where the apex of the heart is located. This anatomical feature allows space for the heart within the thoracic cavity.
The presence of the cardiac notch is one of the reasons the left lung is smaller than the right and contains only two lobes compared to the right lung which contains three.
The lungs are also bordered by the diaphragm, a flat, dome-shaped muscle that is vital for breathing. The hilum is another noteworthy feature of the lungs; it is a concave structure where blood vessels, lymphatic vessels, nerves, and bronchi enter the lung.
When viewed in the context of the respiratory system and the positioning of the heart, these structures highlight the complex relationships between different systems in the body.