Clinical Gross Anatomy of the Chest

-Respiratory tract and Heart

The clinical anatomy of the respiratory tract starts at the external nares or nose. The pig has a large horn plate, perforated by the two nares. This rostal plane or rostrum is used as a rooting and exploration organ and combined with the neck muscles is extremely strong. It is not unusual to have areas of bruising or erosion to the dorsal tip of the rostal plane. The nose is secondarily supported by a bone in the nose – the rostal bone. There are few or no hairs on the external surface of the nares.
Detail of rostal plane with the external nares		Cross-section of the nose at the level between premolar 1 and premolar 2.
Interior to the nares is the nasal cavity which is largely filled by the nasal turbinates. The nasal cavity is divided into two sections by a cartilage septum the nasal septum, which is normally straight. In each of the two nasal chambers there are two outgrowths, on from the dorsal wall as a pundulous outgrowth – the dorsal turbinate and on the lateral wall of the nasal chamber and complex biscrolled structure the ventral turbinate. If the nasal chamber is sectioned in a transverse plane between premolar 1 and premolar 2 the ventral turbinates effectively fill the entire nasal chamber in the normal pig. The position of the premolar 1 and premolar 2 is indicated by the lateral commissure of the mouth. The back of the upper respiratory tract is the tonsils which act as a major lymph node sampling both food and materials brought from the nasal chamber and the trachea/bronchi. The surface of the turbinates are covered in a mucocilary escalator which moves from the nares to the tonsils and oesophagus where the mucus is swallowed and the material killed by the acidic environment.
The middle respiratory tract is defined by the larynx which lies at the root of the tongue. The pig has a large epiglottis which during eating completely protects the entrance of the trachea allowing the pig to eat and breath at the same time.
Root of the tongue and larynx			The entrance to the larynx (hand held)
Ventral to the large epiglottis is a paraepiglottis fold, which can be troublesome when intubating a pig. Intubation is difficult because the larynx can be difficult to visualize as the pig does not have a wide gape. During intubation the tube may miss the larynx and enter the paraepiglottis fold, confusing the clinician into thinking intubation has been successful. Note that in the pig the arytenoids are double.
The general layout of the chest with the ventral surface removed.
				At postmortem the respiratory tract should be removed by making an incision along the medial border of the mandible cutting through the hyoid apparatus and releasing the tongue. Pull the tongue caudally and dissect the larynx and through the chest inlet. The lungs should easily strip away from the pleura. The incision should be continued through the diaphragm ultimately to the rectum. The photograph left demonstrates the “pluck” without the liver and intestines attached.
The trachea starts below the larynx. The trachea is supported by incomplete cartilaginous rings. This assists the clinician as once the larynx is incised the incision can easily be continued right to the bottom of the right and left major bronchi to the bottom of the lung.
Detail of tracheal rings			Detail of right tracheal bronchus
The trachea has three major bronchi, a small right tracheal bronchus which feeds the right apical lobe and the two major bronchi each which feed the rest of the lung. Clinically the right apical lobe is important as this part of the lung is nearest the tonsils and is most susceptible to descending pathogens – for example it is often the most consolidated area in cases of enzootic pneumonia.
Detail of end of bronchi cut surface at the caudal position in the lung.
	The turbinates, trachea and bronchi are lined by a cells covered in cilia. On the surface of the cilia is a mucus layer. This layer, captures in falling particles between 3 and 1.6 mm in size. These particles are then moved by the cilia caudally from the nose to the throat or cranially from the lower bronchi to the throat. The mucociliary escalator is a major component of the defense of the respiratory tract.
Lungs dorsal view
Lung ventral view
The lung can be easily divided into seven distinct lobes – right and left apical, cardiac and diaphragmatic together with the accessory lobe (visible on the dorsal view). During a clinical examination each of these lobes should be examined in detail. The surface of each lobe should be examined for pleurisy. Note the right apical lobe, as described previously. The lung may require to be further dissected to reduce its bulk to allow adequate palpation. The bronchial lymph nodes (of which there are several) should be noted in the mediastinum on the ventral surface after manual partition of each lung.
Once the lung is examined in detail, examine the heart. If there is no gross evidence of any blood vessel abnormalities, such as a patent ductus, remove the heart from the respiratory pluck. Peal away the pericardial sac and examined for pericarditis. Open the heart using four incisions: Incise into the right auricle and continue the incision into the right venticle cutting through the right AV valve. Keep the incision close to the interventiculum septum. Incise into the left auricle and continue the incision into the left venticle cutting through the right AV valve. Keep the incision close to the interventiculum septum. Using the point of the scissors, find and cut into the aorta from the left ventricle Turn the heart over, find and cut into the pulmonary artery from the right ventricle. The heart can now be examined in detail noting the pericardial wall, the right and left AV valves, noting any abnormality of the interventricular septum and finally the pulmonary and aortic valves.
Parietal surface of the heart dorsal view		Parietal surface of the heart ventral view
Heart opened, right side.
Heart opened, left side
The pleura covers both the surface of the lung and the inner wall of the chest. It should be examined in detail for signs of pleurisy.