Lungs Anatomy 

In humans, the trachea divides into the 2 main bronchi that enter the roots of the lungs. The bronchi continue to divide within the lung, & after multiple divisions, give rise to bronchioles. The bronchial tree continues branching until it reaches the level of terminal bronchioles, which lead to alveolar sacs. Alveolar sacs are made up of clusters of alveoli, like individual grapes within a bunch. The individual alveoli are tightly wrapped in blood vessels & it is here that gas exchange actually occurs. Deoxygenated blood from the heart is pumped through the pulmonary artery to the lungs, where oxygen diffuses into blood & is exchanged for carbon dioxide in the hemoglobin of the erythrocytes. The oxygen-rich blood returns to the heart via the pulmonary veins to be pumped back into body systemic circulation.

Human lungs are located in 2 cavities on either side of the heart. Though similar in appearance, the 2 are not identical. Both are separated into lobes by fissures, with 3 lobes on the right & 2 on the left. The lobes are further divided into segments & then into lobules, hexagonal divisions of the lungs that are the smallest subdivision visible to the naked eye. The connective tissue that divides lobules is often blackened in smokers. The medial border of the right lung is nearly vertical, while the left lung contains a cardiac notch. The cardiac notch is a concave impression molded to accommodate the shape of the heart.

Lungs are to a certain extent 'overbuilt' & have a tremendous reserve volume as compared to the oxygen exchange requirements when at rest. Such excess capacity is 1 of the reasons that individuals could smoke for years without having a noticeable decrease in lung role while still or moving slowly in situations like these only a small portion of the lungs are actually perfused with blood for gas exchange. Destruction of too many alveoli over time leads to the condition emphysema, which is associated with extreme shortness of breath. As oxygen requirements increase due to exercise, a greater volume of the lungs is perfused, allowing the body to match its CO₂/O₂ exchange requirements. Additionally, due to the excess capacity, it is possible for humans to live with only 1 lung, with the other compensating for its loss.

The environment of the lung is very moist, which makes it hospitable for bacteria. Many respiratory illnesses are the result of bacterial or viral infection of the lungs. Inflammation of the lungs is known as pneumonia inflammation of the pleura surrounding the lungs is known as pleurisy.

Vital capacity is the maximum volume of air that a person could exhale after maximum inhalation it could be measured with a spirometer. In combination with other physiological measurements, the vital capacity could help make a diagnosis of underlying lung disease.

The lung parenchyma is strictly used to refer solely to alveolar tissue with respiratory bronchioles, alveolar ducts & terminal bronchioles. However, it often includes any form of lung tissue, also including bronchioles, bronchi, blood vessels & lung interstitium.