Dr. Bell's Review of  the
Histology of the Respiratory System

Epiglottis        Trachea        Lung Tissue


The epiglottis prevents food and drrink from entering the lower respiratory tract.  It is made of elastic cartilage.


The trachea is anterior to the esophagus and one of the few patently open tubes in the body.  It has four layers:  mucosa, submucosa, hyaline cartilage and adventitia.

The mucosa is mostly PSCCE.

The submucosa has lots of seromucous glands

The hyaline cartilage occurs in C-shaped rings.  The opening of the C is aligned with the esophagus to facilitate the passage of the bolus.  The ends of the C are connected by a strap of smooth muscle, the trachealis muscle.

The adventitia is made of areolar CT.

Photo by Theresa Carrera

Trachea (50x)

Trachea (100x)  The mucosa is indicated by the blue arrow and lined with PSCCE.  The Submucosa is indicated by the green bracket.  The Hyaline Cartilage ring is indicated by the yellow bracket.  The adventitia is indicated by the periwinkle bracket.

Lung Tissue

Lung tissue has 3 components we will be identifying under the microscope:  alveoli, bronchioles and blood vessels. (To review lung microanatomy).

The alveoli are the microscopic air sacs made of simple squamous epithelium and a little areolar CT.  In addition, they are in closely associated with the pulmonary capillaries (also made of simple squamous epithelium and a little areolar CT.  Together these compose most of the respiratory membrane.

The bronchi are lined with a number of tissues depending upon where in the respiratory tree they are found.  The mucoasal membrane starts as PSCCE in the primary bronchii through tertiary bronchi.  It then transitions to simple ciliated columnar epithelium in the larger bronchioles.  Smaller bronchioles have ciliated simple cuboidal epithelium.  Simple cuboidal epithelium lines the terminal bronchioles.

The blood vessels are lined with simple squamous epithelium and have the three characteristic layers.

Photo by Theresa Carerra

Photo by Theresa Carerra

Designed and constructed by
M. E. Janowski-Bell, Ph.D.
Assistant Professor of Biology
Victoria College