Materials / Reagents Required :

            10 % Neutral Buffered Formalin (NBF), Normal saline (10 litre), 70 % Ethanol (1 litre), different sizes of scissors, forceps, scalpel, spatula, bone cutter, cardboard paper, etc.

Safety Precautions :

            Protective equipments including laboratory coats, gloves, apron, etc., should be worn during euthanasia, necropsy as well as during the preparation of the solutions.

Procedure :

• The trachea of a rat appears as a slightly flattened oval structure about 1.5 to 3 mm in diameter  and 3 to 3.5 cm in length. It divides into the left and right primary bronchi. The right primary bronchus divides into bronchi which conform to the lobes of the right lung, namely the anterior (apical or cranial), middle (cardiac), median (azygous or accessory) and posterior (caudal) lobes.
• The left primary bronchus supplies the left lobe. The bronchus gives rise to smaller secondary bronchi from which the bronchioles originate. The rat lacks the respiratory bronchiole, characteristic of primate lungs including those of humans. The pulmonary acinus, the gas exchange unit, consists of branching alveolar ducts ending blindly in alveolar sacs.
• The lung covered by a thin membranous pleura has a single left lobe and four right lobes. The lung has a double arterial supply with both pulmonary and bronchial arteries. Contrary to other species, the bronchial-pulmonary arterial anastomoses occur near the hilum in the rat. The bronchial arteries supply lungs, lower half of the trachea, bronchi and associated lymph nodes.
• The left and right pulmonary arteries deliver blood to the lung for gas exchange and to the pleura. The branching arteries following the airways extend to the level of the alveolar ducts. The pulmonary venous system drains the pleura, alveoli, bronchioles and most bronchi.
• The veins from the pulmonary lobules join to form pulmonary veins, that join to form a single pulmonary vein draining into the left auricle. The bronchial veins drain the trachea, esophagus, lungs, bronchi and associated lymph nodes and drain into the superior vena cava.
• Noradrenergic nerves enter the lungs in association with the bronchial arteries and are distributed to bronchial artery, medium and small bronchi. Interlobular septa are absent in the rat lung and therefore, secondary pulmonary lobules are absent.

Collection of lungs :

• Thoracic viscera including trachea, thyroid gland, para-thyroid gland and lungs shall be removed as a single structure. Lungs shall be inflated by infusing it with 10 % NBF followed by ligation of the trachea for fixation.
• After induction of anaesthesia/euthanasia, exsanguination shall be accomplished by severing the femoral arteries, abdominal aorta or by incising the skin at the neck region. Normal saline shall be kept ready during the necropsy to keep the lungs moist.
• The fur of the animal shall be moistened with alcohol to prevent the fur from getting adhered into the tissue samples. Skin of the abdomen (in the shape of V) along with mammary gland shall be removed first. The reflected flap of the skin of abdomen is cut to expose the sternum.
• The diaphragm beneath the sternum is cut open and the sternum is removed by two parallel cuts from the xiphoid end up to the first rib. The access to the lungs is facilitated by enlarging the chest open using forceps. Grasp the trachea along with the oesophagus and cut it free from all the underlying attachments.
• Continue cutting the all the remaining attachments below the lungs up to the level of diaphragm. Place the collection on a petri dish and observe the features of the rat lungs.