Trachea and bronchi histology

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Trachea and bronchi histology

USMLE® Step 1 questions

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A study is conducted on the respiratory system to determine the different cell types found in each portion of the respiratory system. A histological examination of the tracheal tissue was performed, and the image under microscope is shown below. Which of the following is true about the cells that are marked by the arrow?    


The trachea is the large airway that extends from the larynx and divides into the two primary bronchi.

Because the trachea and bronchi share similar functions, their walls are composed of similar tissue types as well, but with a few key differences.

Let’s first look at a low power image of the trachea, stained with Hematoxylin and eosin, or H&E for short.

At this magnification, we can easily see the C-shaped cartilage ring, which is unique to the trachea.

Also, you can use the cartilage ring to determine the orientation of the image, since the closed side of the ring points anteriorly and the open side of the ring will always face posteriorly towards the esophagus.

The free ends of the ring are connected to one another by smooth muscle, called the trachealis muscle.

The smooth muscle can be differentiated from the surrounding tissue by the long appearance of their cell bodies when cut longitudinally.

Their lack of striations also indicates that the muscle is smooth muscle, not skeletal muscle.

In older individuals, portions of the tracheal cartilage can transform into bone.

For example, this cross-section of a hen’s trachea shows areas of calcification, with some hyaline cartilage still present on the right.

Looking at the epithelium at 10x magnification, it’s easier to see the different layers of the trachea.

The lumen of the airway is seen at the bottom left of this image.

So, the very thin layer lining the trachea’s respiratory epithelium.

Zooming in much further to approx 100x, the cells that make up the epithelium can be distinguished more easily.

Similar to the nasal and bronchial epithelium, the tracheal epithelium contains three main types of cells: ciliated pseudostratified columnar cells, the pale-staining mucus-secreting goblet cells, and basal cells which are found closer to the basement membrane.


The trachea is the large airway that extends from the larynx and divides into the two primary bronchi. The trachea and bronchi are lined with respiratory epithelium, a specialized type of epithelial tissue that functions to protect the lungs from inhaled particles and microorganisms. The tracheal and bronchial walls share a lot of characteristics. They both contain ciliated pseudostratified columnar epithelium with goblet cells, seromucous glands, smooth muscle, and cartilaginous support. Some of their main differences include the trachea's unique C-shaped cartilage rings with smooth muscle that connects the two ends of the ring, whereas the bronchi have interconnected cartilage plates instead. Also, the bronchi have shorter epithelial cells, fewer goblet cells, and fewer seromucous glands compared with the trachea.


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