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The Canine Respiratory System

Respiration is the function that allows an organism to
take in oxygen and eliminate carbon dioxide.
A dog's respiratory system can be divided into two parts:
the upper respiratory tract and the lower respiratory tract.

The Upper Respiratory Tract

The upper respiratory tract consists of the nasal cavities, the nasopharynx, the larynx and the trachea. The nasal cavities are located in the bridge of the nose and in the forehead and are open to the outside world via the nostrils, which open from the nose. The nostrils have a cartilaginous structure and are mostly open to allow air to enter.

Upper Respiratory Tract NASAL CAVITIES
1. Nasal bone
2. Premaxilla
3. Maxillary bone
4. Lateral cartilage
5. Nasal septum

- The nasal cavities and nasopharynx. The nasal cavities include turbinate bones and nasal sinuses and are separated by a median bony partition. The turbinate bones spiral in on themselves to form a cone shape. For this reason, the mucous membrane that covers them has an extensive surface area, richly furnished with blood vessels, which enhances its role of warming the air and saturating it with water vapor.

The nasal glands contained within the nasal cavities secrete mucus, which traps noxious particles from the air (dust, microbes, etc.). Another portion of the mucous membrane has an olfactory function, allowing the dog to smell.

After leaving the nasal cavities, the air passes through the posterior nares into the nasopharynx in the back of the mouth. At this point, it is nearly at body temperature and impurities have been removed.

- The larynx. The air continues its passage to the lungs through the larynx and trachea. The larynx is composed of four cartilage structures (the cricoid cartilage, thyroid cartilage, arytenoid cartilage and epiglottis) and is attached to the bones of the skull by the hyoid bone. A number of muscles are responsible for moving the cartilage structures in relation to each other so that the larynx is open during respiration but closes when the dog swallows, thus avoiding entry of food into the trachea if it is swallowed the wrong way. The larynx controls the flow of air by opening or closing. It also contains the vocal cords, which vibrate when air passes through them, allowing the dog to make sounds (for example, growling and barking).

- The trachea is a long tube formed of about 40 cartilaginous rings closed by tracheal muscle. It carries the air from the larynx (in the throat) to the bronchi (in the thoracic cavity). Tracheal muscle contracts the trachea, reducing its diameter and so regulating the flow of air: It also prevents excessive dilation, e.g., when the dog coughs.

The Lower Respiratory Tract

Lower Respiratory Tract OVERVIEW OF THE RESPIRATORY TRACT
1. Nasal cavity
2. Frontal sinus
3. Naris
4. Pharynx
5. Larynx
6. Oesophagus
7. Trachea
8. End of trachea
9. Basal margin of left lung
10. Projection of the diaphragm
11. Left lung

The lower respiratory tract includes the bronchi and the lungs, located inside the thoracic cavity and separated from it by the pleurae. The dog's thoracic cavity is defined by the ribs on the sides and by the diaphragm at the rear. The lungs are separated from the chest wall by the pleurae, which define the pleural cavity. Thus, the lungs always remain filled with air. A dog's lungs have seven pulmonary lobes: The left lung has three (cranial, middle and caudal) and the right lung has four (cranial, middle, caudal and accessory).

The bronchi branch and carry the air to the pulmonary alveolae: There are as many bronchi as there are pulmonary lobes. After reaching the lobes, the bronchi again branch into bronchioles of decreasing diameter.

The lungs are also richly supplied with blood vessels, which allow the exchange of oxygen and carbon dioxide (oxygenation) over a large surface area.

Source: Royal Canin Dog Encyclopedia
©2000-2006 Royal Canin - All Rights Reserved

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