Difference Between Alveoli and Alveolus

The word alveoli mean small cavities or pits. In the lungs, they refer to the terminal dilatation of tiny air passages, and in the oral cavity, they are the sockets within the jawbone in which the roots of teeth are set. This article describes the structure and the arrangement of the alveoli in the lungs. The singular word of the alveoli is the alveolus where the only difference in between these two words.

Alveoli

The respiratory system comprises the nasal cavity, nasopharyx, larynx, trachea, bronchial tree, and at the end, terminal dilatations forming the alveoli. Each part of the respiratory system is adopted to perform a specific function with regard to the gas exchanging process.

Lungs are made out of a large number of alveoli; the main unit where oxygen required for cellular respiration is absorbed from the atmosphere into the blood vascular system, and carbon dioxide is excreted into the atmosphere. Theses alveoli open to alveolar ducts or to sacs there by to the respiratory bronchioles to the upper respiratory tracts.

Alveolar wall consists of three tissue components; surface epithelium, supporting tissue and the blood vessels. Epithelium provides a continuous lining to each alveolus and consists of two types of cells. Most of the alveolar surface area is covered with large, squamous cells called type I pneumocytes, which forms part of the extremely thin gaseous diffusion barrier and responsible for gas exchange. The other cell type is type II pneumocytes, which secrete a surface-active material called surfactant, which reduces the surface tension within the alveoli preventing alveolar collapse during expiration. Type II pneumocytes are found to retain the capacity for cell division and have the ability to differentiate into type I pneumocytes in response to damage to the alveolar lining. Supporting tissue consists of fine reticular, collagenous and elastic fibers and occasional fibroblasts. Blood vessels mainly the capillaries form an extensive plexus around each alveolus. Migratory macrophages are also present on the epithelial surface and within the alveolar lumen to destroy foreign material such as bacteria.

Alveolus

As mentioned above, the alveolus is the singular form of alveoli. They get together and form a large surface area around 70m2 in both lungs necessary for efficient gas exchange. The structure and arrangement is described above.