Overview
Each lung (pulmo) fills its pleural cavity, from the pleural cupula at the level of the first rib to the diaphragm, which domes far into the thorax. The mediastinum between them holds the heart, trachea and esophagus. The right lung is clearly larger than the left. Relative to its body mass, the bovine has a small lung capacity, which reduces its respiratory reserve.
Lobes and bronchi
- Left lung: cranial lobe, with cranial and caudal parts, and caudal lobe.
- Right lung: cranial lobe, with cranial and caudal parts; middle lobe, caudal lobe and accessory lobe, the last in the mediastinal recess, around the caudal vena cava. The cranial part of the cranial lobe extends in front of the heart.
- Tracheal bronchus (bronchus trachealis): arises from the right wall of the trachea, cranial to the bifurcation, and ventilates the right cranial lobe.
- Lobulation: thick connective tissue septa separate the lobules and show on the surface as a polygonal mosaic. There is hardly any collateral ventilation between lobules, so obstruction of a bronchiole leaves its lobule without air.
Clinical relevance
- Bovine respiratory disease complex ("shipping fever"): transport stress, mixing of animals from different sources and viruses such as bovine respiratory syncytial virus, bovine herpesvirus 1, parainfluenza 3 and bovine viral diarrhoea virus predispose to bacterial infection with Mannheimia haemolytica, Pasteurella multocida, Histophilus somni and Mycoplasma bovis.
- Cranioventral bronchopneumonia: lesions concentrate in the cranial and middle lobes, especially the right cranial lobe, whose short, direct tracheal bronchus receives inhaled agents early. M. haemolytica causes fibrinous pleuropneumonia with thickened interlobular septa and a marbled appearance.
- Lobulation and emphysema: the lack of collateral ventilation favours lobular atelectasis, and alveolar rupture spreads air along the thick septa (interstitial emphysema).
- Atypical interstitial pneumonia: a sudden move to lush pasture can cause acute pulmonary oedema and emphysema (through 3-methylindole formed in the rumen from tryptophan).
- Dictyocaulosis: Dictyocaulus viviparus mainly affects the caudal lobes, with coughing in young grazing cattle.
- Bovine tuberculosis: Mycobacterium bovis forms granulomas in the lung and in the tracheobronchial and mediastinal lymph nodes.
- Auscultation: the accessible lung field is small, because the thoracic limb covers the cranial part and the diaphragm limits the caudal part.