CRR Histology Lab 4
Airways and Lung
CRR Week 5
Today our goal is observation and appreciation of the tissue composition of the respiratory system. A histology atlas
should help with orientation to the basic features of each slide.
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Trachea, slides 61, 62.
Pharyngeal tonsil, slide 94.
In the tracheal epithelium -- Try to find cilia, goblet
cells (may be inconspicuous), nuclei at different levels
(hence, "pseudostratified" columnar epithelium). Refer to
electron micrographs (e.g., Rhodin atlas) for finer
resolution.
Deeper in the tracheal wall -- ordinary connective
tissue, hyaline cartilage, smooth muscle.
Venous plexus -- On slide 62 look for the venous
plexus in connective tissue of the mucosa, between the
epithelium and the cartilage.
This slide represents your first introduction to lymphoid
tissue. Notice the following.
Lymphocytes -- large crowds of small, dark nuclei
(lymphocytes) characterize most lymphoid tissue.
Lymph nodules -- Lymphocytes are organized into
oval clusters called lymph nodules (or lymphoid follicles).
These are most conspicuous at low power, where the
germinal center of each nodule (where lymphocytes are
proliferating) appears paler than the surrounding mass of
lymphocytes migrating in and out of the germinal centers.
Crypts -- Tonsilar lymphoid tissue is arranged around
crevices or pockets, lined by epithelium, which fold into the
tonsil. In tonsils of the pharynx, these crevices are lined by
respiratory-type epithelium (ciliated pseudostratified
columnar). Lymphocytes wander freely across this
epithelium and may obscure its appearance.
For comparison -- Tonsils of the oral cavity, including
the soft palate, are lined by stratified squamous epithelium.
On slide 93, compare the crypt epithelium with that seen in
the pharyngeal tonsil.
Lung, slide 60 (also, the appropriate SAQ slide).
This is the principal slide for study during this laboratory.
Note that specimens in different slide boxes (i.e., your
colleague's slides) may display different appearances. You
should attempt to find and recognize the following.
Bronchi and bronchioles -- Distinguish larger air
passages (with cartilage and glands; epithelium may include
goblet cells; these may not be present on all specimens)
from smaller ones (without cartilage, lined by ciliated
simple cuboidal epithelium).
Blood vessels -- Remember that pulmonary circulation
is lower-pressure than systemic circulation. Veins and
arteries in the lung have thinner walls than vessels of
comparable size elsewhere in the body.
Alveoli and gas exchange surfaces -- Empty air spaces
of alveoli (including alveolar ducts) comprise most of the
volume of the lung. Understand the tissue composition of
the interalveolar septa, including squamous epithelial cells
(type I pneumocytes), cuboidal, surfactant cells (type II
pneumocytes), and capillaries. Refer to electron
micrographs (e.g., Rhodin atlas) for adequate resolution.
Other details which may be visible -- Smooth muscle
(in bronchial walls and in the "knobs" at the entries into
alveoli), alveolar macrophages ("dust cells"), possibly some
lymphocyte accumulations.
Foetal lung, slide 59.
Look at this slide after becoming familiar with normal lung
histology (slide 60).
The basic organizational pattern of the lung is that of a
gland, in which a branching tree of tubes provides
continuity from the body's outside surface inward to a vast
number of epithelial cells. Indeed, the respiratory tract
begins life as an invagination of epithelial (endodermal)
tissue, and embryonic lungs even have the histological
appearance of compound, exocrine glands. Only fairly late
in development do the cuboidal epithelial cells of the
terminal alveoli assume the thin squamous shape that
characterizes the lining of mature gas-exchanging air sacs.
(Some significant secretory function is retained, in the form
of cuboidal, surfactant-producing great alveolar cells, or
type II pneumocytes.)
Olfactory epithelium, slide 58.
This specimen is not especially "important", but it does
display an unusual epithelium. The olfactory cells
themselves have a most remarkable shape (unfortunately,
not readily visible by light microscopy). Read about this
epithelium for special details, and refer to electron
micrographs (e.g., Rhodin atlas) for adequate resolution.
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SAQ slides.
At least one of the CRR SAQ slides should recognizably
represent some region(s) of the respiratory system. Find
any such slide(s), identify the region(s), and repeat
appropriate observation of detailed features. This slide may
show some features better than the comparable slide in your
reference set.
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ELECTRON MICROGRAPHS
Find examples of alveolar wall / gas exchange membrane,
squamous (type I) pneumocytes, alveolar capillaries,
ciliated cells (and cilia), goblet cells.
At your discretion, you may notify an instructor
for a brief oral evaluation on this material.
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