The lungs are located in the chest, behind the rib cage on either side of the heart. They are roughly conical in shape with a rounded point at their apex and a flatter base where they meet the diaphragm.
Although they are a pair, the lungs are not equal in size and shape.
The left lung has an indentation bordering where the heart resides, called the cardiac notch. The right lung is shorter to allow space for the liver below.
Overall, the left lung has a slightly smaller weight and capacity than the right.
The lungs are surrounded by two membranes, known as the pulmonary pleurae. The inner layer directly lines the outer surface of the lungs, and the outer layer is attached to the inner wall of the rib cage.
The space between the two membranes is filled with pleural fluid.
The lungs’ main role is to bring in air from the atmosphere and pass oxygen into the bloodstream. From there, it circulates to the rest of the body.
Help is required from structures outside of the lungs in order to breathe properly. To breathe, we use the muscle of the diaphragm, the intercostal muscles (between the ribs), the muscles of the abdomen, and sometimes even muscles in the neck.
The diaphragm is a muscle that is domed at the top and sits below the lungs. It powers most of the work involved in breathing.
As it contracts, it moves down, allowing more space in the chest cavity and increasing the lungs’ capacity to expand. As the chest cavity volume increases, the pressure inside goes down, and air is sucked in through the nose or mouth and down into the lungs.
As the diaphragm relaxes and returns to its resting position, the lung volume decreases because the pressure inside the chest cavity goes up, and the lungs expel the air.
The lungs are like bellows. As they expand, air is sucked in for oxygen. As they compress, the exchanged carbon dioxide waste is pushed back out during exhalation.
When air enters the nose or mouth, it travels down the trachea, also called the windpipe. After this, it reaches a section called the carina. At the carina, the windpipe splits into two, creating two mainstem bronchi. One leads to the left lung and the other to the right lung.
From there, like branches on a tree, the pipe-like bronchi split again into smaller bronchi and then even smaller bronchioles. This ever-decreasing pipework eventually terminates in the alveoli, which are little air sac endings.
Here, gas exchange occurs.