The trachea is a flexible tube held open by rings of cartilage, rather like a vacuum-cleaner hose, as shown above. If it was not held open, it would collapse when the animal tried to breath in. The continuity of each ring of cartilage is broken by a small dorsal gap.

This image shows a transverse section through tracheal cartilage.

The trachea divides into two bronchi at a "Y" fork (Figure 1-15).


The bronchi connect with the right and left lungs, where they branch into progressively smaller ducts called bronchioles.


The trachea, bronchi and bronchioles are lined with ciliated epithelium and mucous glands, as seen in the image above which is a transverse section through the wall of the trachea. The cilia seen in a row across the top of the cells in tha image above (facing into the lumen of the trachea) are extremely fine whip-like hairs on the lumenal surfaces of cells. A complex system of mobile protein strands along the length of each cilium provides the motive power for movements that appear whip-like. Millions of cilia beat in a coordinated manner so that they can propel a continuous stream of mucus from the lungs to the nasal cavity. Thus, any small particles that have entered the lungs, despite the protective filtering of incoming air by the turbinate bones, can be removed.

Beef Lung

Gaseous exchange

Pork Lung

Pleural membranes

When the lungs are removed from the body, slippery pleural membranes may be seen covering both the inner surface of the thoracic cavity and the lung surface. Pleural membranes prevent friction between the lungs and the body wall.

Inspiration and expiration

Caused by movements of the intercostal muscles, the ribs, the diaphragm and, sometimes, the abdominal muscles.


The diaphragm resembles a strong drumskin that divides the thoracic and abdominal cavities, but it is thickened by muscle where it joins the body wall. In a dressed carcass, the muscular part of the diaphragm remains as a flap of muscle running diagonally across the inside of the ribcage.


The proteins of the lungs (as well as those of the rumen and spleen), may be recovered by alkaline extraction followed by reacidification. Protein may be isolated as a powder or texturized to form fibers. Lungs also may be processed to isolate heparin, an anticoagulant for medical use.


The respiratory system in poultry is quite different from that found in mammals (Figure 1-15). The lung is the red tissue in the image above.

The lungs of poultry are usually removed with a suction tube during commercial slaughter procedures whereas, in meat animals, the lungs are removed together with the trachea, bronchi and heart, as plucks.

The extensive system of AIR SACS in poultry extends between many of the viscera and even into certain bones.

Air sacs have extremely thin walls and, when poultry are dissected, they should be identified while the viscera are in a relatively undisturbed condition.