• The trachea is a large air tube
• The trachea divides when it reaches the thorax into the left and right bronchi.
• The wall of the trachea is supported by C-shaped cartilage rings.
• The rings are open dorsally where the trachea and oesophagus are closely opposed to avoid friction during swallowing.
• The trachea is lined by ciliated epithelium containing goblet cells secreting mucus. The cilia waft the mucus dorsally toward the pharynx where it can be swallowed
• Dog/ cat- Divided into Lobes by Fissures
• Left Lung – 3 lobes
• Cranial, middle, & caudal lobes
• Right Lung – 4 lobes
• Additional Accessory lobe
• The lungs of the horse show almost no lobation, and the right lung of the horse lacks a middle lobe.
• Lungs of ruminants and pigs are obviously lobed.
Thoracic cavity – pleura
• A vacuum exists within the pleural cavity which is essential for normal and efficient respiration
• The pleural cavity is divided into two separate cavities: – the right and left pleural cavities.
Mediastinum
• Most of the organs in the thoracic cavity lie in the space between the two layers of the mediastinal pleura. They are the: -
• Heart
• Trachea
• Oesophagus
• Major blood vessels
external respiration
needs to be a constant flow into the lungs
lungs are not muscular so can not work be themselves. This means that the diaphragm and the thoracic wall are what the lungs are dependent on
inspiration
1. contraction of the intercostal muscles lifts the ribcage upwards and forwards.
2. The diaphragm contracts and pulls downwards.
3. This increases the volume of the thorax causes the lungs to expand.
Expiration
1. This happens as the chest muscles and thorax relax.
2. Thoracic volume reduces and air is forced out of the lungs
Respiratory muscles
Intercostal muscles lie in the space between the ribs and form the wall of the thorax.
The diaphragm from the caudal boundaries in the thoracic cavity.
Mechanism of breathing
In order to draw air into the lungs, the pressure of air has to drop below atmospheric pressure.
Expanding the volume of lung drops the pressure to facilitate this process.
This increase the volume in the thorax. The vacuum between the lungs and the thorax wall pull the tissue to force respiration process.
Expiration
