Anatomy and physiology

• The upper respiratory tract ends at the cricoid cartilage following the larynx
• The hyoid bone is at the level of C3
• The laryngeal prominence of the thyroid cartilage is known as the adams apple
• The cricoid cartilage is the only complete cartilage ring in the airways
• The pharynx consists of:

  • nasopharynx
  • Oropharynx
  • Laryngopharynx
• the oropharynx extends from the soft palate to the epiglottis, it contains the tonsils which are part of the immune system
• The recurrent laryngeal nerve is a branch of the vagus nerve
• The left recurrent laryngeal nerve is found inferior to the aortic arch- is is longer than the right nerve so is more often injured or involved in pathology
• The right recurrent laryngeal nerve loops around the right subclavian artery
• The recurrent laryngeal nerves are the main nerve supply to the vocal cord muscles

  Bilateral nerve paralysis will lead to stridor from serious airway compromise
• Carina = at the level of T4/5 where the trachea bifurcates

  Can be felt externally as the angle of louie
• Tracheal rings are incomplete circles of cartilage that form the trachea
• Trachea bifurcates into the left and right main bronchus

  Right main bronchus enters both the superior and middle lobes
• Right inferior lobe is mostly posterior
• The hilum of the lungs is the only point of entry and exit for blood vessels

  Sits at the level of T5/6
• 98% of blood entering the lungs is deoxygenated from the pulmonary arteries

  Enters the lungs for gas exchange
• 2% of blood entering the lungs is oxygenated from the bronchial arteries that supply the lung tissue itself
• Venous drainage of the lungs is via the bronchial veins

  • Right bronchial vein drains into the azygos vein
  • Left bronchial vein drains into the accessory hemi-azygos vein
• Trachea originates at the lower end of the larynx - the cricoid cartilage at C6
• C-shaped hyaline cartilage supports the walls of the trachea
• The right main bronchi is straighter and wider than the left and therefore foreign bodies are more likely to be lodged there
• The right lung has 3 lobes: superior, middle and inferior lobes
• The right lung has 2 fissures: horizontal and oblique fissures
• The left lung has 2 lobes and 1 fissure

  • Superior lobe
  • Inferior lobe
  • Oblique fissure
• Sections of the lung are called lobes but on a chest x-ray they are described as zones:

  • Apical zone= above the clavicles
  • Upper zone= below the clavicles and above the cardiac silhouette
  • Mid zone= level of the hilar structures
  • Lower zone= bases of the lungs
• The right and left lungs are separated by pleura- disease should not spread to other lung
• The visceral pleura is a thin membrane that lines the inside of the lungs
• The parietal pleura is the outer layer of pleura and is attached to the diaphragm
• The pleural cavity is the space between the two layers of pleura
• The parietal pleura is sensitive to pressure, pain and temperature

  Supply is from phrenic and intercostal nerves
• Pleurisy is inflammation of the pleura which causes sharp stabbing pains when breathing deeply or coughing
• Atelectasis is collapse of part of the lung due to blockage of airways (e.g. mucus) or lack of expansion (e.g. trauma)
• The horizontal fissure of the right tongue is along the 4th costal cartilages in line with the mid axillary line
• The oblique fissures go from T3 round to the 6th costal cartilage just medical to the mid clavicular line
• The space between the lung bases and the parietal pleura is called the costodiaphragmatic recess

  This is where an effusion would collect
• Tertiary bronchi supply bronchopulmonary segments
• Within the lungs, the main (primary) bronchi branch into lobar (secondary) bronchi. Each secondary bronchi supplies a lobe of the lung, thus there are 3 right lobar bronchi and 2 left. The lobar bronchi then bifurcate into several segmental (tertiary) bronchi, each of which supplies a bronchopulmonary segment. Bronchopulmonary segments are subdivisions of the lung lobes, and act as the functional unit of the lungs
• Gravity and posture can affect draining of bronchopulmonary segments. When supine the superior segment of the lower lobes are the most inferior. This leads to atelectasis (localised collapse)
• Initially there are many generations of conducting bronchioles, which transport air but lack glands and are not involved in gas exchange. Conducting bronchioles then eventually end as terminal bronchioles. These terminal bronchioles branch even further into respiratory bronchioles, which are distinguishable by the presence of alveoli extending from their lumens
• Types of alveolar cells:

  • Type I - gas exchange
  • Type II - secrete pulmonary surfactant