Rodents are a class of mammals that include rats, mice, squirrels, gerbils, beavers, guinea pigs and other animals that have sharp incisor teeth. Rodents' respiratory system is similar to that of most other mammals, including humans. The respiratory system is used to inhale oxygen and exhale carbon dioxide. The rodent respiratory system consists of nostrils, lungs, a trachea and a larynx, though the size of these parts varies based on the size of the rodent.
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Nostrils, Glottis and Pharynx
Rodents inhale and exhale through their nostrils. The nostril cavities are two small openings on the nose, separated by a septum. Air is brought in through these cavities and passed into the pharynx, then into the trachea and lungs. As a rodent is inhaling, the glottis, a small flap in the rodent's throat, closes to prevent food particles from entering the pharynx. This prevents the rodent from choking on food particles. Small rodents, such as mice, have smaller hearts that beat faster than the hearts of larger rodents, so these rodents breathe more frequently.
Trachea and Bronchi
The trachea is a tube, in the upper portion of the rodent's chest, that connects the pharynx and nasal cavities to the lung. The trachea, which is also called windpipe, is supported by rings of cartilage that prevent the tube from collapsing. Closer to the lungs, this pipe branches out into two tubes that are called bronchi. A right bronchus and a left bronchus connect the trachea to each corresponding lung cavity. Each bronchus connects to smaller bronchioles inside the lung cavity.
Larynx and Diaphragm
Though the larynx is not used for respiration, respiration is essential for the larynx because the sounds a rodent uses to communicate are generated by the passage of air through it. The larynx can be tightened or loosened to create the squeaks and other noises common to rodents. The diaphragm sits just below the lungs and looks like a sheet of muscle. The diaphragm helps aid the movement of the lungs as the rodents breathe.
Lungs and Ribs
The lungs are the primary organ of the rodent respiratory system. These two sacs that sit on either side of the rodent's heart and fill with air during inhalation. Each sac contains various branches of brachiole, as well as microscopic units called alveoli. The alveoli help assist the rodent with cardiac respiration. The walls of the lungs are quite thinly lined with pleura so that blood and gas pass through and are absorbed properly. Because of this, the lungs require the protection of the rib cage, which is a series of bones that encase the lungs.