Pulmonary alveoli seen under the microscope

An alveolus (plural: alveoli, from Latin alveolus, “little cavity”) is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the terminal ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well. Via Facebook.

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3 Responses to Pulmonary alveoli seen under the microscope

  1. Phil Krause says:

    It’s interesting that they talk about the respiratory tree. Between the conducting airways and the alveoli sacs where the air exchange takes place, there is an ever decreasing size of branches similar to a tree’s branches. The final step in a tree’s branches would be the leaves. A tree typically has seven ever decreasing generations of branches before you get to the leaves which are only found on the outside. You don’t see many leaves inside the tree as they wouldn’t get much sunlight. In the respiratory tree there are 23 generations of branches and the alveoli sacs are everywhere at the last generation, not just on the outside.
    These 300 million alveoli are completely covered in capillaries; totalling 70 square meters of surface area where the gas exchange takes place. This is where the air in you lungs dissolves into your blood. Oxygen diffuses in while carbon dioxide diffuses out down their concentration gradients. For comparison, we only have about 1.75 square meters of skin so nowhere near enough to satisfy our gas exchange requirements. The blood flowing through the capillaries over your alveoli at any one time is about 70ml. This is about 1/5 of a pop can of blood covering 70 square meters. Imagine trying to paint 70 square meters with 1/5 of a pop can of paint. The blood covering your capillaries is continuously flowing and being replaced about once a second. So the entire 70 square meters is replaced once every second. The deeper you look into anatomy and physiology the more amazing it becomes. What a machine!

  2. alfy says:

    The alveoli are here seen under a scanning electron microscope, not a light microscope. Hence the pin-sharp clarity, and the absence of a depth of field. It is a section, so the thin-ness of the walls stands out, and the dimpled surface of the back wall.

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