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

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.

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.

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.

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.

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.

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.

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.

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?

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?

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.

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).. end