Respiratory System chapter 25

• Respiratory system


  • Anatomically divided into upper and lower respiratory tracts
  • Functionally divided into a conducting portion and a respiratory portion
• Respiratory system functions


  • Pulmonary ventilation (inhalation and exhalation)
  • Gas exchange
  • Gas conditioning (warming, humidifying, and cleaning)
  • Sound production
  • Olfaction
  • Defense
• Upper respiratory tract


  • Includes nose and nasal cavities, paranasal sinuses, pharynx
  • Within conducting portion of respiratory system
• Nose and nasal cavity


  • Main conducting airway for inhaled air
  • Nasal cavity begins as internal component of nose and ends at choanae
• Nasal cavity


  • Mostly lined with pseudostratified epithelium
  • Nasal septum divides it into right and left portions
  • Superior, middle and inferior nasal conchae form lateral wall and condition air
• Paranasal sinuses


  Air spaces that make bones lighter and are named after the bones they reside in
• Pharynx


  • Commonly called the throat, shared by respiratory and digestive tracts
  • Divided into nasopharynx, oropharynx, and laryngopharynx
  • Lined with mucosa and has skeletal muscle for swallowing control
• Nasopharynx


  Posterior to nasal cavity and superior to soft palate, lined with pseudostratified ciliated columnar epithelium
• Oropharynx


  Bounded superiorly by soft palate and inferiorly by hyoid bone, lined with nonkeratinized stratified squamous epithelium
• Laryngopharynx


  Starts inferior to hyoid bone and extends to top of esophagus, lined with nonkeratinized stratified squamous epithelium
• Lower respiratory tract


  • Contains conducting portions (larynx, trachea, bronchi, bronchioles, terminal bronchioles) and respiratory portions (respiratory bronchioles, alveolar ducts, alveoli)
  • No gas exchange in conducting portions, respiration occurs in respiratory portions
• Larynx


  • Commonly called the voice box, connects pharynx to trachea
  • Functions include serving as air passageway, preventing ingested materials from entering respiratory tract, producing sound for speech, assisting in increasing abdominal pressure, participating in sneeze and cough reflex
• Larynx


  • Supported by framework of 9 cartilages
  • Thyroid cartilage is largest, with V-shaped anterior projection called laryngeal prominence (Adam's apple)
  • Cricoid cartilage is ring-shaped and inferior to thyroid
  • Epiglottis is spoon-shaped cartilage that closes larynx opening during swallowing
  • Vocal folds vibrate to produce sound when air forced through rima glottidis
• Trachea


  • Commonly called the windpipe, anterior to esophagus, inferior to larynx, and superior to main bronchi
  • Supported by C-shaped tracheal cartilages connected by annular ligaments, with trachealis muscle posteriorly
• Bronchial tree


  • Trachea splits into right and left main bronchi, which continue to branch into progressively smaller tubes
  • Bronchi characteristics: large bronchi lined with pseudostratified epithelium, small bronchi lined with columnar epithelium, ring of smooth muscle between mucosa and cartilage
  • Bronchioles have no cartilage but thick smooth muscle layer, contraction/relaxation causes bronchoconstriction/bronchodilation
• Respiratory bronchioles, alveolar ducts, and pulmonary alveoli

  • Terminal bronchioles branch into respiratory bronchioles, which branch into alveolar ducts ending in alveolar sacs
  • Alveolar wall is thin to facilitate gas diffusion, composed of type I and type II alveolar cells, and contains alveolar macrophages
• Respiratory membrane is the thin wall between alveolar lumen and blood across which gases diffuse, consisting of plasma membranes of alveolar and capillary cells, and fused basement membrane
• Bronchial tree structure


  • Left and right main bronchi
  • Lobar bronchi
  • Segmental bronchi
  • Bronchioles
  • Terminal bronchioles
  • Respiratory bronchioles
  • Alveoli
• Pleura and pleural cavities


  • Outside of lung and inside of thoracic wall lined by pleura, a serous membrane
  • Visceral pleura tightly adheres to lung, parietal pleura lines pleural cavity
• Gross anatomy of the lungs

  • Each lung is conical, with broad inferior base and pointed superior apex
  • Left lung is slightly smaller to accommodate heart, has oblique fissure dividing into superior and inferior lobes
  • Right lung has oblique and horizontal fissures dividing it into superior, middle and inferior lobes
• There are 10 bronchopulmonary segments in the right lung and 8-10 in the left lung, each supplied by its own tertiary bronchus and branch of pulmonary artery and vein
• Blood supply to and from the lungs


  • Pulmonary circulation conducts blood to and from gas exchange surfaces
  • Bronchial circulation is part of systemic circulation that supplies blood to bronchi and bronchioles
• Lymph nodes and vessels are located within the lungs and around the bronchi and pleura
• Pulmonary ventilation


  • Also known as breathing, is the movement of air into and out of the respiratory system
  • Involves four simultaneous processes: pulmonary ventilation, alveolar gas exchange, gas transport in blood, and systemic gas exchange
• Pulmonary ventilation mechanics


  Follow Boyle's law - during inhalation, thoracic cavity volume increases, intrapulmonary pressure decreases, and air flows in; during exhalation, the opposite occurs
• Skeletal muscles of breathing

  • Muscles of quiet breathing (diaphragm, external intercostals)
  • Muscles of forced inhalation (sternocleidomastoid, pectoralis minor, serratus posterior superior, erector spinae)
  • Muscles of forced exhalation (internal intercostals, abdominal muscles, transversus thoracis, serratus posterior inferior)
• Innervation of the respiratory system

  • Skeletal muscles of respiration and sound production have somatic (voluntary) control
  • Larynx, trachea, bronchial tree, and lungs have autonomic (sympathetic and parasympathetic) innervation
• Ventilation control


  Brainstem respiratory center controls rate and depth of breathing
• Respiratory system becomes less efficient with age, resulting in decreased depth and rate of ventilation, and increased risk of obstructive disorders like emphysema and bronchitis