![This is blank.](https://digitalhistology.org/wp-content/themes/histology-unified/imgs/trans.png)
Secondary bronchus
Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x
![Epithelium <p>Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x</p>](https://digitalhistology.org/wp-content/uploads/2018/06/O.R.I.C.SB_.04.P01.png)
Epithelium
Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x
![Lamina propria <p>Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x</p>](https://digitalhistology.org/wp-content/uploads/2018/07/O.R.I.C.SB_.04.P02.png)
Lamina propria
Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x
![- Smooth muscle <p>Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x</p>](https://digitalhistology.org/wp-content/uploads/2018/06/O.R.I.C.SB_.04.P03.png)
- Smooth muscle
Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x
![- Mixed glands <p>Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x</p>](https://digitalhistology.org/wp-content/uploads/2018/06/O.R.I.C.SB_.04.P05.png)
- Mixed glands
Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x
![Cartilage plates <p>Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x</p>](https://digitalhistology.org/wp-content/uploads/2018/06/O.R.I.C.SB_.04.P06.png)
Cartilage plates
Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x
![Bronchial blood vessels <p>Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x</p>](https://digitalhistology.org/wp-content/uploads/2018/06/O.R.I.C.SB_.04.P07.png)
Bronchial blood vessels
Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x
![Alveoli <p>Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x</p>](https://digitalhistology.org/wp-content/uploads/2018/06/O.R.I.C.SB_.04.P08.png)
Alveoli
Secondary bronchi decrease in diameter and each layer becomes thinner, as the bronchi progress into the lungs. 100x
![Image source > <p>This image was taken from a slide in the University of Michigan slide collection.</p>](https://digitalhistology.org/wp-content/uploads/2019/02/Michigan-source-ping-2.png)
Image source >
This image was taken from a slide in the University of Michigan slide collection.