Final answer:
The concave portion of each lung resting on the diaphragm is referred to as the base. The diaphragm is a dome-shaped muscle critical for changing thoracic cavity volume during respiration, and it supports the base of the lungs.
Step-by-step explanation:
The portion of each lung that is concave and lies on the diaphragm is known as the base of the lungs. The diaphragm is a dome-shaped muscle that plays a critical role in breathing by contracting and relaxing to change the volume of the thoracic cavity.
In its relaxed state, it is convex on its superior surface, forming the floor of the thoracic cavity, while its inferior surface is concave, forming the roof of the abdominal cavity. Each lung's base fits snugly against the diaphragm's convex superior surface, effectively resting on this concave muscle during the respiratory cycle.
The lungs are pyramid-shaped, paired organs connected to the trachea by the left and right bronchi and enclosed by the pleurae. The right lung is typically larger with three lobes, while the left lung is smaller with two lobes to accommodate the heart. Within the lungs, the hilum is a concave structure on the mediastinal surface where blood vessels, lymphatic vessels, nerves, and a bronchus enter.
The dynamic movement of the diaphragm during inspiration and expiration is essential for the ventilation process that facilitates the exchange of oxygen and carbon dioxide between the lungs and the atmosphere.