An ultrastructural study of the equine lower respiratory tract.

This research used electron microscopy to study the surface features of the lower respiratory tract in 20 healthy horses of varying ages and types. The study found that the ciliary carpet, a type of cell lining the respiratory tract, was almost entirely present from the trachea to the lobar bronchi. In smaller bronchi, the ciliary carpet was less complete and non-ciliated mucous cells were more prominent.

Methodology

• The researchers studied the surface features of the lower respiratory tract in 20 clinically healthy horses of different ages and types. For the testing, they utilized scanning electron microscopy, allowing them to get details of the specimen at a microscopic level.
• Aside from scanning electron microscopy, the team conducted parallel light microscopic and transmission electron microscopic studies. These methods offered additional approaches for examining and studying the cellular structures of the horse’s lower respiratory tract.

Findings

• The study revealed that the ciliary carpet, otherwise known as the group of cilia-covered cells that lines the respiratory tract, was almost fully present from the trachea to the lobar bronchi (the branches of the bronchi that lead to the lungs’ lobes). The ciliary carpet is vital for trapping and moving particles and pathogens away from the lungs.
• Observations concluded that within smaller bronchi, the ciliary carpet was less complete. This allowed numerous non-ciliated mucous cells to become apparent. These cells, while not possessing the particle-moving cilia, contribute by producing mucus that traps harmful particles.
• Furthermore, the terminal bronchioles, which are primarily populated by non-ciliated bronchiolar epithelial cells, showed a sudden junction with alveolar ducts, the tiny tubes that air travels through in the lungs.
• The study also found the presence of interalveolar pores to be common, particularly in older horses. These small openings between alveoli, the small air sacs in the lungs, allow air and other small particles to pass between them. An increased presence in older horses is of note as alterations in these structures could have implications for respiratory health as horses age.