Lower Respiratory System (Anatomy)

• Factors limiting the size of the thoracic cavity


  • Proximal forelimb & pectoral musculature
  • Thoracic vertebrae spinous processes & epaxial muscles
  • Cranial bulge of the diaphragm
• Pleurae


  Serous membranes
• Pleurae: serous membranes


  1. Thoracic cavity has 2 pleural cavities and mediastinum

  2. Pleural cavities and lungs within them surrounded by pleura: Parietal pleura, Visceral pleura

  3. Functions of pleura: Reduce friction, Ventilation of lungs, Pleurisy/pneumothorax
• Parietal Pleura


  Consists of costal pleura, mediastinal pleura, diaphragmatic pleura
• All parts of Parietal Pleura are continuous with each other
• Cupula pleurae extends beyond thoracic inlet and is vulnerable to injury
• Pleural recesses


  • Costodiaphragmatic recess, Costal pleura, Diaphragmatic pleura
• Diaphragm


  Costodiaphragmatic recess, Costomediastinal recess, Clinically relevant
• Diaphragm is the most important respiratory muscle
• Diaphragm


  • Position: Aorta, Caudal Vena Cava, Oesophagus, Azygous Vein, Cisterna Chyli, Right Phrenic Nerve, Left Phrenic Nerve, Dorsal Vagal Trunk, Ventral Vagal Trunk, aortic hiatus, oesophageal hiatus, caval foramen, Diaphragmatic openings
• Trachea


  • Cartilage, Mucosa, Trachealis muscle
• Trachea


  Runs from cricoid cartilage to bifurcation at base of heart, Cricotracheal ligament, Cartilaginous rings, Trachealis muscle, Respiratory Mucosa
• Species variation in position of trachealis muscle
• Components of the trachea

  • Cricotracheal ligament
  • Cartilaginous rings
  • Trachealis muscle
  • Respiratory Mucosa
• Trachea extends from cricoid cartilage to bifurcation at the base of the heart
• Trachealis muscle is SMOOTH muscle that bridges the gap in cartilage rings, controls the diameter of the trachea, and shows species variation in position
• Respiratory Mucosa


  Pseudostratified columnar ciliated epithelium containing mucous glands
• Tracheal position within the thoracic cavity can be seen in Fig 5.28: Done et al. Colour Atlas of Veterinary Anatomy
• System of airways allowing passage of air to lungs

  • Decrease in size as branch distally
  • Species differences - Tracheal bronchus found in pigs and ruminants
  • Segmental bronchi aerate broncho-pulmonary segments
  • Discrete portions of lung supplied by identifiable bronchi and blood vessels
  • More clinical relevance in humans at present?
• Distal tracheobronchial tree


  Consists of bronchioles and alveoli
• Lungs receive TWO types of blood supply: Pulmonary Circulation and Systemic Circulation
• Lymphatic drainage of lungs includes Pulmonary nodes, Tracheobronchial nodes, Bronchial lymphocentre, Mediastinal lymphocentre, Thoracic duct (L)/right lymphatic duct (R), and Cranial vena cava