 Dear students, in this topic, we shall discuss the functional anatomy of mammalian lungs. The mammalian lungs are located in thoracic cavity or chest cavity. Air enters through the nostrils, then passing through the pharynx, it enters the trachea. Trachea se aage, a system of branching ducts conveys air to the inner of the lungs. This branching network subdivides the trachea and it forms bronchi. These bronchi, they branch profusely, they form after this branching the terminal bronchioles. Terminal bronchioles, they divide and they form respiratory bronchioles. Respiratory bronchioles are connected to a cluster of alveolar ducts or sacs which are called alveoli. These terminal clusters are exactly like this, for example, in any fruit, if we look at gray fruits, then branches are moving, but at the end of the branch, a cluster of small fruits is attached to the branch. Similarly, these alveoli are attached to alveolar ducts, so these alveoli are present. Then the respiratory portion of the lung constitutes the terminal bronchioles, respiratory bronchioles, alveolar ducts and alveolar sacs. These are the places where gas transfer occurs. Most of the gas transfer occurs in alveolar sacs, but alveolar ducts or respiratory bronchioles or terminal bronchioles may be a little bit of a gas exchange because they are in-walled tubules. The extensive branching in the airways which is found in the lungs that results in a decrease in the diameter of individual air ducts from the trachea to the terminal bronchioles. As much as there is a division, the individual airways reduce their diameter. So that the most diameter of the trachea is of the terminal bronchioles. But along with this, where the diameter of the tubules is decreasing, the total cross-sectional area of the airways is increasing rapidly. The gas transfer surface of the lungs has in-walled alveoli. The airways which lead to the terminal bronchioles, terminal bronchioles Airways constitute the non-respiratory portion of the lung. The air ducts which lead to the respiratory portion of the lung contain either cartilage or a little smooth muscle along with cartilage are only the smooth muscle. These features, presence of cartilage and presence of smooth muscle, they prevent the airways from collapse even in unconscious states. The cartilage are smooth muscles which are involuntary.