Respiratory system

The respiratory system is the set of organs that enable gas exchange between an organism and its environment.

The respiratory system is composed of the upper and lower airways:

• The upper airways include the nose (nasal cavity and paranasal sinuses), pharynx, and larynx.

• The lower airways include the trachea, bronchi, bronchioles, and alveoli, which constitute the pulmonary parenchyma.

The anatomy of the respiratory tract varies considerably between species, particularly regarding pulmonary lobation, the presence of interlobular septa, and the type of bronchial branching.

• Dogs and Cats: Their lungs are similar to those of other carnivores. They have well-developed respiratory bronchioles but lack interlobular septa, meaning that lobulation is not visible macroscopically. Their mediastinum is fenestrated, allowing communication between the two pleural cavities.

• Ruminants (Cattle, Sheep): The lungs of cattle, sheep, and pigs share anatomical similarities. They are characterized by very pronounced lobulation, with prominent and thick interlobular septa that clearly divide the pulmonary lobules. Cattle have lungs that are relatively small compared to their body size. Respiratory bronchioles are present in cattle and goats but poorly developed in sheep.

• Horse: The horse has large lungs with poorly marked lobation and incomplete interlobular septa. A unique feature of equids is the presence of the guttural pouches, large diverticula of the auditory tube (Eustachian tube) that open into the nasopharynx. The lungs of the horse lack respiratory bronchioles.

Human respiratory anatomy shares features with several animal species, including the presence of interlobular septa (less pronounced than in ruminants) and respiratory bronchioles (as in dogs and cats). However, it differs in having a dichotomous bronchial branching pattern, unlike the monopodial pattern seen in most domestic mammals. Additionally, humans possess respiratory bronchioles, which are absent in the horse, and have a non fenestrated mediastinum.