Respiratory System Part 2

• Trachea


  Extends from the cricoid cartilage of the larynx to the root of the lung where it bifurcates to form the right and left principal bronchi

  
• Position of trachea


  1. In the cervical region: Ventral to the esophagus, related dorsally to the longus colli and longus capitis muscles

  2. In the thoracic cavity: Continues caudally in the mediastinum, dorsal to the cranial vena cava, crosses the aortic arch on the right side and dorsal to the base of the heart, divides into two principal bronchi at the level of 4th-6th intercostal spaces

  
• Trachea


  • Formed by a series of C-shaped hyaline tracheal cartilages joined by fibroelastic annular ligaments, permits flexibility to follow neck movements, non-collapsible tube, dorsal surface completed by connective tissue and the smooth, transversely oriented trachealis muscle, covered with adventitia and lined with a mucous membrane

  
• Bronchi


  The bronchial tree begins at the bifurcation of the trachea, right and left principal bronchi, lobar bronchi (formerly secondary bronchi) within lung lobes, segmental bronchi (tertiary bronchi)
• Bronchioles


  Airways less than 1 mm in diameter where cartilage disappears, branch into terminal bronchioles, respiratory bronchioles, alveolar ducts and alveolar sacs
• Alveoli


  The place where gas exchange with the blood takes place
• Lungs


  • Consist of left and right, occupy much of the thoracic cavity, not alike in form or size, normal texture is like a sponge, flexible and regains shape quickly after compression, bright pink in colour when fresh
• Lung structure


  • Cone-shaped, with an apex, base and convex lateral (costal) surface, flattened medial surface, concave diaphragmatic surface
• Lung margins


  • Dorsal margin extends from apex to base, ventral margin extends from apex to base and is continuous with basal margin caudally
• Hilus


  Area where principal bronchus, pulmonary vessels, lymphatics and nerves enter and leave the lung, the root of the lung

  
• Lung impressions


  • Cardiac impression on medial surface indented by the heart, aortic and esophageal impressions dorsal to cardiac impression, impression for cranial vena cava on right lung

  
• Lung lobes


  • Cranial lobe (cranial and caudal parts), middle lobe, caudal lobe, accessory lobe
• Lung lobe arrangement in domestic mammals

  • Cattle, goats, pigs, sheep, cats and dogs have same basic arrangement, in horse the lobes are not divided by deep fissures making lobation indistinct, middle lobe absent
• Cranial lobe of cat lung

  • Transversely compressed between heart and lateral thoracic wall, extends from 5th rib to thoracic inlet, caudal part has thin dorsocranially convex border overlying cranial part

  
• Caudal lobe of cat lung

  • Pyramidal in shape, completely separated from cranial lobe by caudal interlobar fissure
• Lobe


  Cranial lobe<|>Middle lobe<|>Caudal lobe<|>Accessory lobe
• Domestic animals


  • Horse
  • Sheep
  • Cattle
  • Pig
  • Cat
• Cranial lobe


  Transversely compressed between the heart and the lateral thoracic wall<|>Extends from the dorsal part of the 5th rib to and through the thoracic inlet
• Caudal part of the cranial lobe


  Thin dorsocranially convex border that overlies the caudal thickened portion of the cranial part of the cranial lobe<|>Cranial and caudal part is separated by cranial interlobar fissure
• Caudal lobe


  Pyramidal in shape<|>Completely separated from the caudal part of the cranial lobe by the caudal interlobar fissure
• Right lung


  Cranial lobe<|>Middle lobe<|>Accessory lobe<|>Caudal lobe
• Cranial lobe of right lung

  Extends from the dorsal part of the cranial interlobar fissure cranially and ventrally to the right of the median plane<|>Separated from the middle lobe by the cranial interlobar fissure
• Middle lobe of right lung

  Costal surface is broad and tapers to a narrow, pyramid-shaped ventral extremity, lies caudal to the heart<|>Medial surface is deeply excavated by the heart, resulting in the cardiac impression

  
• Cardiac notch


  Gap between middle and cranial lobes of the right lung, where the heart makes contact with the thoracic wall
• Accessory lobe


  Irregular shape<|>Caudally it is molded against the diaphragm<|>Cranially it lies in contact with the apex of the heart and the adjacent portion of the right caudal lobe
• Caudal lobe of right lung


  Its diaphragmatic surface is irregularly excavated in its central part by the accessory lobe
• Bronchial circulation


  Provides oxygenated blood and nutrition to the bronchi, lungs, large blood vessels, lymph nodes and visceral pleura
• Pulmonary circulation


  Movement of blood from the heart to the lungs for oxygenation, then back to the heart again
• Vessels supplying the lung

  • Bronchial artery
  • Bronchial vein
  • Pulmonary artery
  • Pulmonary vein
• Bronchial circulation


  Thoracic aorta → bronchoesophageal artery → bronchial arteries → bronchi, lung tissue, lymph nodes, visceral pleura → bronchial vein → azygous vein
• Pulmonary circulation


  Vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein →left atrium → left ventricle → aorta
• Pulmonary nerve plexus


  Delivers nerves to the lungs within the mediastinum, with both sympathetic and parasympathetic (vagal) fibres contributing
• Efferent fibres


  Motor neurons that pass to the bronchial glands and musculature and to the blood vessels
• Afferent fibres


  Sensory neurons that come from the laryngeal, tracheal, bronchial mucosa (cough reflex), from vessels, and from stretch receptors
• Lymphatic drainage of the lung

  Forms superficial and deep networks that collect lymph for the tracheobronchial, pulmonary, and mediastinal nodes
• Lymph nodes of the lung

  • Cranial tracheobronchial
  • Left tracheobronchial
  • Right tracheobronchial
  • Middle tracheobronchial
  • Pulmonary
• Diaphragm


  Separates the thoracic and abdominal cavities<|>Dome-shaped, convex in all directions on its cranial surface<|>Consists of a central tendon and a muscular periphery

  
• Parts of the diaphragm

  • Lumbar portion (pars lumbalis)
  • Costal part (pars costalis)
  • Sternal part (pars sternalis)
• Lumbar portion of diaphragm


  Consists of left and right crura that arise from the ventral border of L4 and the body of L3

  
• Costal part of diaphragm

  Arises from the inner surfaces of the ribs and costal cartilages, attaching in an oblique direction to the 13th through 7th ribs