Lung
(4x objective lens)
-
This low magnification
image of mammalian lung shows examples of many of the air passageways and
respiratory areas of the lung (see the labeled version). Air enters the lung
through intrapulmonary bronchi, which branch into lobar bronchi (secondary
bronchi). Each of these gives rise to several segmental
bronchi, two of which are seen in this section (one is in the center
of the upper half of the image and above and the other is above and to its
left). The bronchi can be distinguished from all other intrapulmonary structures
by the presence of hyaline cartilage in their
walls. The cartilage rings (large bronchi) and plates (smaller bronchi) help
keep the passageways open as the air pressure changes during ventilation.
Spirally arrayed bands of smooth muscle is also
present in the connective tissue of the wall, and control the diameter of
the bronchial lumen. As
in this image, bronchi are accompanied by large blood
vessels. From the bronchi, air then flows into bronchioles,
which lack cartilage and are supported by bands of smooth muscle and elastic
fibers. As the bronchioles branch into smaller and smaller bronchioles, the
epithelium changes from ciliated pseudostratified columnar with goblet cells,
to simple ciliated columnar to non-ciliated columnar/cuboidal. The smallest
bronchioles are called terminal bronchioles.
Air then flows into respiratory bronchioles,
which have walls that are thin enough is some places to allow gas exchange
to occur. Terminal bronchioles mark the beginning of the respiratory area
of the lung. Air then flows into alveolar ducts,
alveolar sacs and alveoli.
Alveoli make up the bulk of the volume of the lung.
- Stain = Iron
Hematoxylin & Eosin
Click
anywhere in the image to see a labeled version.
Copyright
Paul B. Bell, Jr. & Barbara Safiejko-Mroczka
The
University of Oklahoma
Version 010603