1. HISTOLOGY REVIEW Respiratory System
Dr. Tim Ballard
Department of Biology and Marine Biology
UNC Wilmington

2. Trachea trachea – section – H&E – 4x objective adventitia
C-shaped ring of hyaline cartilage
submucosa
mucosa
lumen lined with ciliated pseudostratified columnar epithelium
The trachea has a large diameter, so it is hard to see the entire structure using the 4X objective. Therefore, it is important to scroll through the slide to see the whole organ. Identify the layers, and then zoom in.

3. ciliated pseudostratified columnar epithelium
Trachea
trachea –section – H&E – 10x objective
ciliated pseudostratified columnar epithelium
adventitia
submucosa
lumen
hyaline cartilage
adipose tissue
The basic structure of the trachea continues through the level of the primary bronchus. It will change as the bronchus moves into the substance of the lung.

4. Trachea
trachea – section – H&E – 40x objective
cilia
ciliated pseudostratified columnar epithelium
submucosa
hyaline cartilage
Although not shown in this view, goblet cells should be seen scattered throughout the epithelial layer.

5. Intrapulmonary bronchus
intrapulmonary bronchus – cross section – H&E – 4x objective
lumen lined with ciliated pseudostratified columnar epithelium
As the primary bronchus moves into the substance of the lungs, the C-shaped cartilage begins to break into plates of cartilage surrounding the lumen. Scroll around the slide to identify these structures.
The arrows show plates of cartilage, not a C-shaped ring. This is a diagnostic feature of this type of bronchus. Very little smooth muscle is present.

6. Bronchiole
bronchiole – cross section – H&E – 10x objective
alveolus
branch of pulmonary artery
branch of pulmonary vein *
As the intrapulmonary bronchi continue to divide the cartilage plates become increasingly smaller, until they are gone, and smooth muscle is appearing. At this point, the tubes are called bronchioles
The asterisk shows a bronchiole. Note that there are no plates of cartilage around it.

7. Bronchiole
bronchiole – cross section – H&E – 40x objective
smooth muscle
bronchiolar epithelium is transitioning from ciliated pseudostratified columnar to ciliated low columnar in this section
As the bronchioles lead to the alveoli, the epithelium becomes increasingly shorter, loses its goblet cells, and then its cilia, eventually giving rise to the simple squamous epithelia of the alveoli.
Note the change in the epithelium to a short columnar/cuboidal with no goblet cells. Cilia are still present.

8. ciliated simple columnar epithelium
Bronchiole
bronchiole – cross section – H&E – 40x objective
ciliated simple columnar epithelium
smooth muscle
Note the change in the epithelium to a short columnar/cuboidal with no goblet cells. Cilia are still present.

9. Respiratory bronchiole
respiratory bronchiole – cross section – H&E – 40x objective
respiratory membrane with simple squamous epithelium
respiratory bronchiole with simple cuboidal epithelium
In this section, we see a respiratory bronchiole giving rise to alveoli. Can you see the pink-stained RBCs in the respiratory membrane?

10. Respiratory bronchiole
respiratory bronchiole – cross section – H&E – 40x objective
respiratory membrane with simple squamous epithelium
alveolus
respiratory bronchiole with simple cuboidal epithelium becoming simple squamous
alveolus
alveolus
In this section, we see a respiratory bronchiole giving rise to alveoli. Can you see the pink-stained RBCs in the respiratory membrane?

11. Alveoli
lung– section – H&E – 4x objective
bronchiole
alveoli
The terminal branches of the bronchioles become alveolar ducts, that give rise to alveolar sacs, formed by individual alveoli.
In a low-power view, we see that the lung is formed almost completely of alveoli, air sacs where gas exchange with the blood occurs.

12. respiratory membrane with simple squamous epithelium
Alveoli
alveolus – section – H&E – 40x objective
capillary
respiratory membrane with simple squamous epithelium
Review through multiple areas of respiratory membrane. Identify RBCs and study its overall thinness (0.5µ)..
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