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Lung Anatomy: The Airway and Alveoli

These tiny little membranous sacs, bundled along and terminating at the bronchioles, provide an extremely large surface area for gas exchange between the atmosphere and the blood. The alveolar surface area is approximately the size of a tennis court. You can calculate this yourself with the simple algebraic equation 4πr2: 300,000,000 alveoli x 4πr2 where r is the 0.165 millimeter radius of an alveoli This is only a crude estimation. Alveoli are not really perfect little spheres as often depicted; they have irregular shapes and sizes. Though they are about one-third of a millimeter in diameter on average, they increase in size with inhalation and decrease with exhalation. And 300,000,000 is…

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 New part of the body found hiding in the lungs

The cells, known as respiratory airway secretory (RAS) cells, are found in tiny, branching passages known as bronchioles, which are tipped with alveoli, the teensy air sacs that exchange oxygen and carbon dioxide with the bloodstream. The new RAS cells are similar to stem cells — "blank canvas" cells that can differentiate into any other type of cell in the body — and are capable of repairing damaged alveoli cells and transforming into new ones.

Articles of Interest

Alveoli of Lungs

The total respiratory surface of human lungs is about 100 m2 , equal to the surface area of a racquetball court!

Alveoli: Gas Exchange

The alveoli ("many alveoli", "one alveolus") are the sites of gas exchange in the lungs. They are tiny air sacks sometimes described as being cauliflower-shaped. Oxygen diffuses across the lining of the alveoli and blood capillaries into and into red blood cells. Carbon dioxide diffuses from the blood to the alveoli. A concentration gradient is maintained by breathing as well as blood flow.

Pulmonary Alveoli and Gas Exchange

The exchange portion of the respiratory system is anatomically designed for gas exchange. The exchange portion starts at the level of the respiratory bronchioles of the lungs, which is the first level where alveoli make their appearance within the respiratory system. Alveoli are anatomical structures within the lung that are specialized for gas exchange. The shape of the squamous epithelium allows for the creation of a large surface area and a very thin diffusion barrier, both of which facilitate gas exchange. In addition, the alveoli have a very high degree of vascularity. Three types of cells are found within the alveoli:

Artificial breathing system reveals alveoli function in lungs

Chip mimics inhalation and exhalation, allowing scientists to study flow patterns in the bronchial network.

Hunger Disease and Pulmonary Alveoli

“The time was 1940, the place the Jewish ghetto in Warsaw, Poland. The Nazis had sealed several hundred thousand people off from the outside world, determined to starve them to death”. Remarkable Jewish physician-scientists, themselves starving, conceived and completed a clinicopathologic study and smuggled the manuscript out of the ghetto to Professor Orlowski of Warsaw University. He buried it until it could be safely reclaimed

Pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis (PAM) is a fascinating rare lung disease that is associated with the accumulation of hydroxyapatite microliths within the lumen of the alveolar spaces. In most patients, PAM is discovered incidentally on radiographs performed for other purposes, and the typical disease course is characterised by slowly progressive respiratory insufficiency over decades.

Pulmonary Alveolar Proteinosis

Pulmonary alveolar proteinosis (PAP) is a rare lung disease involving surfactant accumulation within the alveoli resulting from decreased clearance, rather than increased production. This condition can be congenital, secondary, or autoimmune. Autoimmune PAP is the most common pathophysiologic mechanism accounting for 90 percent of documented cases.

The Number of Alveoli in the Human Lung

Although the question “How many alveoli are there in the human lung?” (3–5) seems to be a very simple one, it is indeed difficult to answer in practice. This is largely due to the fact that alveoli are not discrete, separate particles but rather a set of open saccules or pronounced surface irregularities with openings making them impossible to define unambiguously in single histologic sections. Knowing the alveolar number, however, is of general importance for the understanding of lung development and disease.

Resources

Physiopedia

Pulmonary alveolus ( plural: alveoli) are tiny air sacs that function as basic respiratory units. It is a hollow cup-shaped cavity in the lung parenchyma, where gas exchange takes place. Lung alveoli are found in the acini at the beginning of the respiratory zone. They are located sparsely in the respiratory bronchioles, lining the walls of the alveolar ducts. The alveoli are located in the alveolar sacs of the lungs in the pulmonary lobules of the respiratory zone. They are more numerous in the blind-ended alveolar sacs.[1]

Radiopaedia

Alveoli contain two major types of epithelial cells . The most abundant, type 1 pneumocytes (95%) are squamous cells in which gas exchange occurs. The remaining 5%, type 2 pneumocytes, are granular cells which secrete surfactant. Surfactant is a lipoprotein with a high phospholipid content which reduces surface tension. This increases pulmonary compliance, prevents atelectasis and aids recruitment of collapsed airways.

StatPearls

Alveoli represent the major sites of gas exchange. Their presence increases the surface area of the lung to maximize gas exchange, much like villi and microvilli increase the absorptive surface area of the digestive tract. For alveoli to carry out their function efficiently, they must be both a dynamic and stable system. The lung parenchyma must be able to expand and recoil during inspiration and expiration, and the air-blood barrier must be thin to allow for gas exchange to occur.